Add method to read bright star catalog and find bright stars in sky region

ctapipe/utils/__init__.py

@@ -6,6 +6,7 @@
 from .unstructured_interpolator import UnstructuredInterpolator
 from .datasets import (find_all_matching_datasets, get_table_dataset, get_dataset_path,
                        find_in_path)
+from .astro import get_bright_stars
 from .CutFlow import CutFlow, PureCountingCut, UndefinedCut
 
 
@@ -19,6 +20,7 @@
     'get_table_dataset',
     'get_dataset_path',
     'find_in_path',
+    'get_bright_stars',
     'CutFlow',
     'PureCountingCut',
     'UndefinedCut',

ctapipe/utils/astro.py

@@ -0,0 +1,63 @@
+# Licensed under a 3-clause BSD style license - see LICENSE.rst
+"""
+This module is intended to contain astronomy-related helper tools which are
+not provided by external packages and/or to satisfy particular needs of
+usage within ctapipe.
+"""
+from astropy.coordinates import Angle
+from astropy.coordinates import SkyCoord
+from astropy import units as u
+
+__all__ = ['get_bright_stars']
+
+
+def get_bright_stars(pointing=None, radius=None, magnitude_cut=None):
+    """
+    Returns an astropy table containing star positions above a given magnitude within
+    a given radius around a position in the sky, using the Yale bright star catalog
+    which needs to be present in the ctapipe-extra package. The included Yale bright
+    star catalog contains all 9096 stars, excluding the Nova objects present in the
+    original catalog from  Hoffleit & Jaschek (1991),
+    http://adsabs.harvard.edu/abs/1991bsc..book.....H, and is complete down to
+    magnitude ~6.5, while the faintest included star has mag=7.96.
+
+    Parameters
+    ----------
+    pointing: astropy Skycoord
+       pointing direction in the sky (if none is given, full sky is returned)
+    radius: astropy angular units
+       Radius of the sky region around pointing position. Default: full sky
+    magnitude_cut: float
+        Return only stars above a given magnitude. Default: None (all entries)
+
+    Returns
+    -------
+    Astropy table:
+       List of all stars after cuts with names, catalog numbers, magnitudes,
+       and coordinates
+    """
+    from ctapipe.utils import get_table_dataset
+
+    catalog = get_table_dataset("yale_bright_star_catalog5",
+                                role="bright star catalog")
+
+    starpositions = SkyCoord(ra=Angle(catalog['RAJ2000'], unit=u.deg),
+                             dec=Angle(catalog['DEJ2000'], unit=u.deg),
+                             frame='icrs', copy=False)
+    catalog['ra_dec'] = starpositions
+
+    if magnitude_cut is not None:
+        catalog = catalog[catalog['Vmag'] < magnitude_cut]
+
+    if radius is not None:
+        if pointing is None:
+            raise ValueError('Sky pointing, pointing=SkyCoord(), must be '
+                             'provided if radius is given.')
+        separations = catalog['ra_dec'].separation(pointing)
+        catalog['separation'] = separations
+        catalog = catalog[separations < radius]
+
+    catalog.remove_columns(['RAJ2000', 'DEJ2000'])
+
+    return catalog
+

ctapipe/utils/tests/test_astro.py

@@ -0,0 +1,19 @@
+# Licensed under a 3-clause BSD style license - see LICENSE.rst
+"""
+This module contains the utils.astro unit tests
+"""
+from ..astro import get_bright_stars
+from astropy.coordinates import SkyCoord
+from astropy import units as u
+
+def test_get_bright_stars():
+    """
+    unit test for utils.astro.get_bright_stars(). Tests that only Zeta Tau is
+    returned close to the Crab Nebula as object brighter than mag=3.5.
+    """
+    pointing = SkyCoord(ra=83.275 * u.deg, dec=21.791 * u.deg, frame='icrs')
+
+    table = get_bright_stars(pointing, radius=2. * u.deg, magnitude_cut=3.5)
+
+    assert len(table) == 1
+    assert table[0]['Name'] == '123Zet Tau'

docs/ctapipe_api/utils/index.rst

@@ -58,6 +58,9 @@ Reference/API
 .. automodapi:: ctapipe.utils
     :no-inheritance-diagram:
 
+.. automodapi:: ctapipe.utils.astro
+    :no-inheritance-diagram:
+
 .. automodapi:: ctapipe.utils.linalg
     :no-inheritance-diagram:
 

environment.yml

@@ -39,7 +39,7 @@ dependencies:
   - pytables
   - tqdm
   - conda-forge::nbsphinx
-  - ctapipe-extra=0.2.17
+  - ctapipe-extra=0.2.18
   - pytest-runner
   - pip:
     - eventio~=0.20.1

py3.6_env.yaml

@@ -40,7 +40,7 @@ dependencies:
   - tqdm
   - conda-forge::nbsphinx
   - pytest-runner
-  - ctapipe-extra=0.2.17
+  - ctapipe-extra=0.2.18
   - pyhessio=2.1
   - nbconvert>=5.4
   - pip:

py3.7_env.yaml

@@ -40,7 +40,7 @@ dependencies:
   - tqdm
   - conda-forge::nbsphinx
   - pytest-runner
-  - ctapipe-extra=0.2.17
+  - ctapipe-extra=0.2.18
   - pyhessio=2.1
   - nbconvert>=5.4
   - pip: