Closed stellaCL closed 6 years ago
This is surprising because I checked against SVO quite recently.
if I just look at the description of the filter:
>>> lib['GROUND_JOHNSON_V'].info()
Filter object information:
name: GROUND_JOHNSON_V
detector type: energy
wavelength units: AA
central wavelength: 5504.666021 angstrom
pivot wavelength: 5492.885092 angstrom
effective wavelength: 5438.689405 angstrom
norm: 870.650149
definition contains 10000 points
Zeropoints
Vega: 21.099109 mag,
3.6337607043700736e-09 erg / angstrom * centimeter ** 2 * second,
3657.0984273591766 Jy
AB: 21.106951 mag,
3.607610771896633e-09 erg / angstrom * centimeter ** 2 * second,
3630.7805477010147 Jy
ST: 21.100000 mag,
3.6307805477010028e-09 erg / angstrom * centimeter ** 2 * second,
3654.0991307201225 Jy
And if I simply plot the filter, I obtain something similar to your red curve:
>>> f = lib['GROUND_JOHNSON_V']
>>> plt.plot(f.wavelength.to('AA').magnitude, f.transmit)
Could it be that you plotted without the wavelength vector as x-values? It seems you'd find it starts at 0 and ends at 10 000.
I guess I can close this issue then. Re-open it if needed.
Hi, I noticed that the transmission curve of GROUND_JOHNSON_B is incorrect... I get the following when plotting it:
Can you explain why this makes you think this is incorrect?
The y-axis. The transmision should always be a number between 0 and 1
Calculations are independent of the normalization of the filters. I suppose it is a percent transmission unit.
But from what I saw in your code, in the case of apply_transmision you multiply the transmision curve to the flux, so having the curve go to values such as 70 would make the flux stronger, unless I skipped the part where you ignore the fact that its values are > 1
EDIT: Also, why would only the B band be a percent unit and not the other Johnson filters
Hi,
Can I ask how did you define the filters in Pyphot, because I noticed that at least some of them do not match with archival values?
I made a plot of a 20,000K blackbody and then plotted the transmission curves of you Ground_Johnson_V and HST_WFPC2_F555W with the corresponding filters from the SVO Filter Profile Service, and they do not match. Most importantly the f.transmit() for the Pyphot Ground Johnson V filter shows that the filter has a bandwidth of over 3000 Angstrom and it peaks around 3000 Angstrom.
I am attaching a copy of that plot