Source code for astroquery.alfalfa.core

# Licensed under a 3-clause BSD style license - see LICENSE.rst
Author: Jordan Mirocha
Affiliation: University of Colorado at Boulder
Created on: Fri May  3 09:45:13 2013

import requests
import numpy as np
import as ma
from astropy import units as u
from astropy import coordinates as coord
from ..utils import commons
from ..query import BaseQuery

__all__ = ['Alfalfa', 'AlfalfaClass']

# have to skip because it tries to use the internet, which is not allowed
__doctest_skip__ = ['AlfalfaClass.query_region', 'Alfalfa.query_region']

[docs] class AlfalfaClass(BaseQuery): CATALOG_PREFIX = "" PLACEHOLDER = -999999
[docs] def get_catalog(self): """ Download catalog of ALFALFA source properties. Notes ----- This catalog has ~15,000 entries, so after it's downloaded, it is made global to save some time later. Returns ------- result : Dictionary of results, each element is a masked array. """ if hasattr(self, 'ALFALFACAT'): return self.ALFALFACAT result = requests.get(self.CATALOG_PREFIX) iterable_lines = result.text.split('\n') # Read header cols = iterable_lines[0].split(',') catalog = {} for col in cols: catalog[col] = [] # Parse result for line in iterable_lines[1:]: # skip blank lines or trailing newlines if line == "": continue col_values = line.split(',') for i, col in enumerate(cols): item = col_values[i].strip() if item == '\"\"': catalog[col].append(self.PLACEHOLDER) elif item.isdigit(): catalog[col].append(int(item)) elif item.replace('.', '').isdigit(): catalog[col].append(float(item)) else: catalog[col].append(item) result.close() # Mask out blank elements for col in cols: mask = np.zeros(len(catalog[col]), dtype='bool') # need to turn list -> array for boolean comparison colArr = np.array(catalog[col]) # placeholder must share Type with the array ph = np.array(self.PLACEHOLDER, dtype=colArr.dtype) mask[colArr == ph] = True catalog[col] = ma.array(catalog[col], mask=mask) # Make this globally available so we don't have to re-download it # again in this session self.ALFALFACAT = catalog return catalog
[docs] def query_region(self, coordinates, *, radius=3. * u.arcmin, optical_counterpart=False): """ Perform object cross-ID in ALFALFA. Search for objects near position (ra, dec) within some radius. Parameters ---------- coordinates : str or `astropy.coordinates` object The target around which to search. It may be specified as a string in which case it is resolved using online services or as the appropriate `astropy.coordinates` object. ICRS coordinates may also be entered as strings as specified in the `astropy.coordinates` module. radius : str or `~astropy.units.Quantity` object, optional The string must be parsable by `astropy.coordinates.Angle`. The appropriate `~astropy.units.Quantity` object from `astropy.units` may also be used. Defaults to 3 arcmin. optical_counterpart : bool Search for position match using radio positions or position of any optical counterpart identified by ALFALFA team? Keep in mind that the ALFA beam size is about 3x3 arcminutes. See documentation for astropy.coordinates.angles for more information about ('ra', 'dec', 'unit') parameters. Examples -------- >>> from astroquery.alfalfa import Alfalfa >>> from astropy import coordinates as coords >>> C = coords.SkyCoord('0h8m05.63s +14d50m23.3s') >>> agc = Alfalfa.query_region(C,'3 arcmin') Returns ------- result : AGC number for object nearest supplied position. """ coordinates = commons.parse_coordinates(coordinates) ra = dec = dr = coord.Angle(radius).deg cat = self.get_catalog() # Use RA and DEC to find appropriate AGC if optical_counterpart: ra_ref = cat['RAdeg_OC'] dec_ref = cat['DECdeg_OC'] else: ra_ref = cat['RAdeg_HI'] dec_ref = cat['Decdeg_HI'] dra = np.abs(ra_ref - ra) \ * np.cos(dec * np.pi / 180.) ddec = np.abs(dec_ref - dec) sep = np.sqrt(dra ** 2 + ddec ** 2) i_minsep = np.argmin(sep) minsep = sep[i_minsep] # Matched object within our search radius? if minsep < dr: return cat['AGCNr'][i_minsep] else: return None
Alfalfa = AlfalfaClass()