Getting Started#
Exposure time to counts#
Given an exposure time, spectral type, and V magnitude, what are the counts and signal-to-noise ratios we can collect using ARCES on the ARC 3.5 m Telescope at Apache Point Observatory?
First, let’s import the packages we’ll use:
import matplotlib.pyplot as plt
import astropy.units as u
from arcesetc import plot_order_counts, plot_order_sn
Then let’s specify the properties of the observation that we’re going to make:
sptype = 'G4V'
wavelength = 6562 * u.Angstrom
exp_time = 30 * u.min
V = 10
Now let’s make a plot of the number of counts we can expect in the order
containing wavelength
, using plot_order_counts
:
fig, ax, exp_time = plot_order_counts(sptype, wavelength, V, exp_time=exp_time)
plt.show()
(Source code
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, hires.png
, pdf
, svg
)
Similarly, we can plot the signal-to-noise ratio using plot_order_sn
like so:
fig, ax, exp_time = plot_order_sn(sptype, wavelength, V, exp_time=exp_time)
plt.show()
(Source code
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, hires.png
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Note
The spectral type output by the arcesetc
package (G5V
) isn’t
exactly the same as the one we requested (G4V
). That’s because the
package is giving you the nearest spectral type available in the library of
spectra.
Signal-to-noise to exposure time#
Given a S/N at a particular wavelength, what’s the appropriate exposure time? We
can find out by supplying the desired signal_to_noise
, and arcesetc
will
compute the exposure time for you:
import matplotlib.pyplot as plt
import astropy.units as u
from arcesetc import plot_order_sn
sptype = 'B3V'
wavelength = 3990 * u.Angstrom
signal_to_noise = 100
V = 5
fig, ax, exp_time = plot_order_sn(sptype, wavelength, V, signal_to_noise=signal_to_noise)
plt.show()
(Source code
, png
, hires.png
, pdf
, svg
)
Wolf-Rayet Star#
We presently have one Wolf-Rayet star of spectral type WN8h
.
You can see the funky effects of the strong emission lines on the S/N near
H-alpha, for example:
import astropy.units as u
from arcesetc import plot_order_sn
sptype = 'WN8h'
wavelength = 6562 * u.Angstrom
signal_to_noise = 30
V = 14
fig, ax, exp_time = plot_order_sn(sptype, wavelength, V, signal_to_noise=signal_to_noise)
plt.show()
(Source code
, png
, hires.png
, pdf
, svg
)