def test_snr_normalization(desired_snr, band, testing_spectrum):
"""Test SNR after normalizing function is the desired value.
Testing on middle of J band.
"""
wav, flux = testing_spectrum
band_mid = utils.band_middle(band)
# Searching for the closest index to 1.25
index_reference = np.searchsorted(wav, [band_mid])[0]
snr_estimate = np.sqrt(
np.sum(flux[index_reference - 1:index_reference + 2]))
assert round(snr_estimate, 1) != desired_snr # Assert SNR is not correct
norm_const = snrnorm.snr_constant_band(wav,
flux,
snr=desired_snr,
band=band)
new_flux = flux / norm_const
new_snr_estimate = np.sqrt(
np.sum(new_flux[index_reference - 1:index_reference + 2]))
assert round(new_snr_estimate, 0) == desired_snr
def test_snr_normalization_constant(desired_snr, band, testing_spectrum):
"""Test snr_constant_band and snr_constant_wav produce same result."""
wav, flux = testing_spectrum
band_mid = utils.band_middle(band)
assert snrnorm.snr_constant_band(
wav, flux, band=band, snr=desired_snr
) == snrnorm.snr_constant_wav(wav, flux, band_mid, snr=desired_snr)
def test_band_middle(band):
"""Test band middle is middle of band.
Some repeated coding.
"""
lower, upper = utils.band_limits(band)
middle = utils.band_middle(band)
assert lower < middle
assert middle < upper
assert (lower + upper) / 2 == middle
def snr_constant_band(
wav: ndarray,
flux: ndarray,
snr: Union[int, float] = 100,
band: str = "J",
sampling: Union[int, float] = 3.0,
verbose: bool = False,
) -> float:
"""Determine the normalization constant to achieve a SNR in the middle of a given band.
SNR estimated by the square root of the number of photons in a resolution element.
Parameters
----------
wav: ndarray
Wavelength array in microns.
flux: ndarray
Photon flux array (photons/s/cm**2).
snr: int or float
SNR per resolution element to achieve. Default is 100.
band: str
Band to use for normalization. Default is "J".
sampling: int or float
Number of pixels per resolution element. Default is 3.
verbose: bool
Enable verbose. Default is False.
Returns
-------
norm_value: float
Normalization value to divide spectrum by to achieve a
signal-to-noise level of snr within an resolution element
in the middle of the band.
Note
----
This is a wrapper around `snr_constant_wav`, using the band center.
Warning
-------
Wavelength is expected in microns!
"""
band_middle = utils.band_middle(band)
if not (wav[0] < band_middle < wav[-1]):
raise ValueError("Band center not in wavelength range.")
return snr_constant_wav(wav,
flux,
wav_ref=band_middle,
snr=snr,
sampling=sampling,
verbose=verbose)
def test_snr_constant_band_returns_mid_value_const(band):
size = 100
np.random.seed(40)
flux = 500 * np.random.rand(
size
) # To give a random spectrum (but consistent between tests)
lim = utils.band_limits(band)
wav = np.linspace(lim[0], lim[1], size)
band_const = snrnorm.snr_constant_band(wav, flux, band=band)
wav_const = snrnorm.snr_constant_wav(wav, flux, wav_ref=utils.band_middle(band))
assert isinstance(band_const, float)
assert isinstance(wav_const, float)
assert band_const == wav_const # Since band calls wave at midpoint
def snr_constant_band(
wav: ndarray,
flux: ndarray,
snr: Union[int, float] = 100,
band: str = "J",
sampling: Union[int, float] = 3.0,
) -> float:
"""Determine the normalization constant to achieve a SNR in the middle of a given band.
SNR estimated by the square root of the number of photons in a resolution element.
Parameters
----------
wav: ndarray
Wavelength array (microns)
flux: ndarray
Photon flux array (photons/s/cm**2)
snr: int, default = 100
SNR to normalize to.
band: str, default = "J"
Band to use for normalization.
sampling: int or float
Number of pixels per resolution element.
Returns
-------
normalization_value: float
Normalization value to divide spectrum by to achieve a
signal-to-noise level of snr within an resolution element
in the middle of the band.
Note
----
If sampling is a float it will rounded to the nearest integer for indexing.
"""
band_middle = utils.band_middle(band)
if not (wav[0] < band_middle < wav[-1]):
raise ValueError("Band center not in wavelength range.")
norm_constant = snr_constant_wav(
wav, flux, wav_ref=band_middle, snr=snr, sampling=sampling
)
return norm_constant
def test_band_midpoint_j():
"""Middle of J is 1.25 microns."""
assert utils.band_middle("J") == 1.25
def do_analysis(
star_params,
vsini: float,
R: float,
band: str,
sampling: float = 3.0,
conv_kwargs=None,
snr: float = 100.0,
ref_band: str = "J",
rv: float = 0.0,
air: bool = False,
model: str = "aces",
verbose: bool = False,
) -> Tuple[Quantity, ...]:
"""Calculate RV precision and Quality for specific parameter set.
Parameters
----------
star_param:
Stellar parameters [temp, logg, feh, alpha] for phoenix model libraries.
vsini: float
Stellar equatorial rotation.
R: float
Instrumental resolution.
band: str
Spectral band.
sampling: float (default=False)
Per pixel sampling (after convolutions)
conv_kwargs: Dict (default=None)
Arguments specific for the convolutions,
'epsilon', 'fwhm_lim', 'num_procs', 'normalize', 'verbose'.
snr: float (default=100)
SNR normalization level. SNR per pixel and the center of the ref_band.
ref_band: str (default="J")
Reference band for SNR normalization.
rv: float
Radial velocity in km/s (default = 0.0).
air: bool
Get model in air wavelengths (default=False).
model: str
Name of synthetic library (aces, btsettl) to use. Default = 'aces'.
verbose:
Enable verbose (default=False).
Returns
-------
q: astropy.Quality
Spectral quality.
result_1: astropy.Quality
RV precision under condition 1.
result_2 : astropy.Quality
RV precision under condition 2.
result_3: astropy.Quality
RV precision under condition 3.
Notes
-----
We apply the radial velocity doppler shift after
- convolution (rotation and resolution)
- resampling
- SNR normalization.
in this way the RV only effects the precision due to the telluric mask interaction.
Physically the RV should be applied between the rotational and instrumental convolution
but we assume this effect is negligible.
"""
if conv_kwargs is None:
conv_kwargs = {
"epsilon": 0.6,
"fwhm_lim": 5.0,
"num_procs": num_cpu_minus_1,
"normalize": True,
"verbose": verbose,
}
if ref_band.upper() == "SELF":
ref_band = band
model = check_model(model)
if model == "aces":
wav, flux = load_aces_spectrum(star_params, photons=True, air=air)
elif model == "btsettl":
wav, flux = load_btsettl_spectrum(star_params, photons=True, air=air)
else:
raise Exception("Invalid model name reached.")
wav_grid, sampled_flux = convolve_and_resample(wav, flux, vsini, R, band,
sampling, **conv_kwargs)
# Doppler shift
try:
if rv != 0:
sampled_flux = doppler_shift_flux(wav_grid, sampled_flux, vel=rv)
except Exception as e:
print("Doppler shift was unsuccessful")
raise e
# Scale normalization for precision
wav_ref, sampled_ref = convolve_and_resample(wav, flux, vsini, R, ref_band,
sampling, **conv_kwargs)
snr_normalize = snr_constant_band(wav_ref,
sampled_ref,
snr=snr,
band=ref_band,
sampling=sampling,
verbose=verbose)
sampled_flux = sampled_flux / snr_normalize
if (ref_band == band) and verbose:
mid_point = band_middle(ref_band)
index_ref = np.searchsorted(
wav_grid,
mid_point) # searching for the index closer to 1.25 micron
snr_estimate = np.sqrt(
np.sum(sampled_flux[index_ref - 1:index_ref + 2]))
print(
"\tSanity Check: The S/N at {0:4.02} micron = {1:4.2f}, (should be {2:g})."
.format(mid_point, snr_estimate, snr))
# Load Atmosphere for this band.
atm = Atmosphere.from_band(band=band, bary=True).at(wav_grid)
assert np.allclose(atm.wl,
wav_grid), "The atmosphere does not cover the wav_grid"
# Spectral Quality/Precision
q = quality(wav_grid, sampled_flux)
# Precision given by the first condition:
result_1 = rv_precision(wav_grid, sampled_flux, mask=None)
# Precision as given by the second condition
result_2 = rv_precision(wav_grid, sampled_flux, mask=atm.mask)
# Precision as given by the third condition: M = T**2
result_3 = rv_precision(wav_grid, sampled_flux, mask=atm.transmission**2)
# Turn quality back into a Quantity (to give it a .value method)
q = q * u.dimensionless_unscaled
return q, result_1, result_2, result_3
def do_analysis(
star_params,
vsini: float,
R: float,
band: str,
sampling: float = 3.0,
conv_kwargs=None,
snr: float = 100.0,
ref_band: str = "J",
rv: float = 0.0,
air: bool = False,
model="phoenix",
):
"""Precision and Quality for specific parameter set.
Parameters
----------
air: bool
Get model in air wavelengths.
model: str
Name of synthetic library to use. (phoenix, btsettl).
rv: float
Radial velocity.
Notes:
We apply the radial velocity doppler shift after
- convolution (rotation and resolution)
- resampling
- SNR normalization.
in this way the RV only effects the precision due to the telluric mask interaction.
The RV should maybe come between the rotational and instrumental convolution
but we assume this effect is negligible.
"""
if conv_kwargs is None:
conv_kwargs = {
"epsilon": 0.6,
"fwhm_lim": 5.0,
"num_procs": num_procs_minus_1,
"normalize": True,
}
if ref_band.upper() == "SELF":
ref_band = band
if model == "phoenix":
# Full photon count spectrum
wav, flux = load_aces_spectrum(star_params, photons=True, air=air)
elif model == "btsettl":
wav, flux = load_btsettl_spectrum(star_params, photons=True, air=air)
else:
raise ValueError(
"Model name error in '{}'. Valid choices are 'phoenix and 'btsettl'"
.format(model))
wav_grid, sampled_flux = convolve_and_resample(wav, flux, vsini, R, band,
sampling, **conv_kwargs)
# Doppler shift
try:
if rv != 0:
sampled_flux = doppler_shift_flux(wav_grid, sampled_flux, vel=rv)
except Exception as e:
print("Doppler shift was unsuccessful")
raise e
# Spectral Quality
q = quality(wav_grid, sampled_flux)
# Scale normalization for precision
wav_ref, sampled_ref = convolve_and_resample(wav, flux, vsini, R, ref_band,
sampling, **conv_kwargs)
snr_normalize = snr_constant_band(wav_ref,
sampled_ref,
snr=snr,
band=ref_band,
sampling=sampling)
sampled_flux = sampled_flux / snr_normalize
if ref_band == band:
mid_point = band_middle(ref_band)
index_ref = np.searchsorted(
wav_grid,
mid_point) # searching for the index closer to 1.25 micron
snr_estimate = np.sqrt(
np.sum(sampled_flux[index_ref - 1:index_ref + 2]))
print(
"\tSanity Check: The S/N at {0:4.02} micron = {1:4.2f}, (should be {2:g})."
.format(mid_point, snr_estimate, snr))
# Load Atmosphere for this band.
atm = Atmosphere.from_band(band=band, bary=True).at(wav_grid)
assert np.allclose(atm.wl,
wav_grid), "The atmosphere does not cover the wav_grid"
# Spectral Quality/Precision
q = quality(wav_grid, sampled_flux)
# Precision given by the first condition:
prec1 = rv_precision(wav_grid, sampled_flux, mask=None)
# Precision as given by the second condition
prec2 = rv_precision(wav_grid, sampled_flux, mask=atm.mask)
# Precision as given by the third condition: M = T**2
prec3 = rv_precision(wav_grid, sampled_flux, mask=atm.transmission**2)
# Turn quality back into a Quantity (to give it a .value method)
q = q * u.dimensionless_unscaled
return [q, prec1, prec2, prec3]
