import numpy as np
import pandas as pd
from astropy import units as u
from astropy.coordinates import SkyCoord
from astropy.table import Table
from stellarphot import apass_dr9, vsx_vizier
__all__ = ["read_file", "set_up", "crossmatch_APASS2VSX", "mag_scale", "in_field"]
DESC_STYLE = {"description_width": "initial"}
[docs]
def read_file(radec_file):
"""
Read an AIJ radec file with target and/or comparison positions
Parameters
----------
radec_file : str
Name of the file
Returns
-------
`astropy.table.Table`
Table with target information, including a
`astropy.coordinates.SkyCoord` column.
"""
df = pd.read_csv(radec_file, names=["RA", "Dec", "a", "b", "Mag"])
target_table = Table.from_pandas(df)
ra = target_table["RA"]
dec = target_table["Dec"]
target_table["coords"] = SkyCoord(ra=ra, dec=dec, unit=(u.hour, u.degree))
return target_table
[docs]
def set_up(ccd):
"""
Read in sample image and find known variables in the field of view.
Parameters
----------
ccd: `astropy.nddata.CCDData`
Sample image.
Returns
-------
vsx: `astropy.table.Table`
Table with known variables in the field of view.
"""
try:
vsx = vsx_vizier(ccd.wcs, radius=0.5 * u.degree)
except RuntimeError:
vsx = []
else:
ra = vsx["ra"]
dec = vsx["dec"]
vsx["coords"] = SkyCoord(ra=ra, dec=dec, unit=u.degree)
# Restrict to just the stars in the field of view
if len(vsx):
good_stars = np.ones(len(vsx), dtype=bool)
vsx = in_field(vsx["coords"], ccd, vsx, good_stars)
return vsx
[docs]
def crossmatch_APASS2VSX(CCD, RD, vsx):
"""
Find APASS stars in FOV and matches APASS stars to VSX and APASS to input targets.
Parameters
----------
CCD : `astropy.nddata.CCDData`
Sample image.
RD : `astropy.table.Table`
Table with target information, including a
`astropy.coordinates.SkyCoord` column.
vsx : `astropy.table.Table`
Table with known variables in the field of view.
Returns
-------
apass : `stellarphot.CatalogData`
Table with APASS stars in the field of view.
v_angle : `astropy.units.Quantity`
Angular separation between APASS stars and VSX stars.
RD_angle : `astropy.units.Quantity`
Angular separation between APASS stars and input targets.
"""
apass = apass_dr9(CCD.wcs)
# Use the standard names we have introduced for ra and dec
ra = apass["ra"]
dec = apass["dec"]
# Coordinate units are in degrees now
apass["coords"] = SkyCoord(ra=ra, dec=dec, unit=u.degree)
apass_coord = apass["coords"]
if vsx:
v_index, v_angle, v_dist = apass_coord.match_to_catalog_sky(vsx["coords"])
else:
v_angle = []
if RD:
RD_index, RD_angle, RD_dist = apass_coord.match_to_catalog_sky(RD["coords"])
else:
RD_angle = []
return apass, v_angle, RD_angle
[docs]
def mag_scale(
cmag, apass, v_angle, RD_angle, brighter_dmag=0.44, dimmer_dmag=0.75, passband="SR"
):
"""
Select comparison stars that are 1) not close the VSX stars or to other
target stars and 2) fall within a particular magnitude range.
Parameters
----------
cmag : float
Magnitude of the target star.
apass : `astropy.table.Table`
Table with APASS stars in the field of view.
v_angle : `astropy.units.Quantity`
Angular separation between APASS stars and VSX stars.
RD_angle : `astropy.units.Quantity`
Angular separation between APASS stars and input targets.
brighter_dmag : float, optional
Maximum difference in magnitude between the target and comparison stars.
dimmer_dmag : float, optional
Minimum difference in magnitude between the target and comparison stars.
passband : str, optional
Passband to use for selecting the comparison stars.
Returns
-------
apass_good_coord : `astropy.coordinates.SkyCoord`
Coordinates of the comparison stars.
good_stars : `astropy.table.Table`
Table with the comparison stars.
"""
good_filter = apass["passband"] == passband
high_mag = apass["mag"] < cmag + dimmer_dmag
low_mag = apass["mag"] > cmag - brighter_dmag
too_close = 2.0 * u.arcsec
if len(v_angle) > 0:
good_v_angle = v_angle > too_close
else:
good_v_angle = True
if len(RD_angle) > 0:
good_RD_angle = RD_angle > too_close
else:
good_RD_angle = True
good_stars = good_filter & high_mag & low_mag & good_RD_angle & good_v_angle
good_apass = apass[good_stars]
apass_good_coord = good_apass["coords"]
return apass_good_coord, good_stars
[docs]
def in_field(apass_good_coord, ccd, apass, good_stars):
"""
Return APASS stars in the field of view.
Parameters
----------
apass_good_coord : `astropy.coordinates.SkyCoord`
Coordinates of the comparison stars.
ccd : `astropy.nddata.CCDData`
Sample image.
apass : `astropy.table.Table`
Table with APASS stars in the field of view.
good_stars : bool array
Boolean array indicating which stars are good.
Returns
-------
ent : `astropy.table.Table`
Table with APASS stars in the field of view.
"""
apassx, apassy = ccd.wcs.all_world2pix(apass_good_coord.ra, apass_good_coord.dec, 0)
ccdx, ccdy = ccd.shape
xin = (apassx < ccdx) & (0 < apassx)
yin = (apassy < ccdy) & (0 < apassy)
xy_in = xin & yin
apass_good_coord[xy_in]
nt = apass[good_stars]
ent = nt[xy_in]
return ent
