Week 2: Updates and a second to-do list

We’ve made some headway with the synphot tutorial, which has helped us determine what to do next. This is what we’ve done so far:

• To get more accurate count rates, we:
  • Add effects by atmospheric attentuation by using the Cerro Paranal model transmittance curves for an airmass of 1.5
  • Consider the effects of the quantum efficiency on the spectra by using the values in the table found in section 3.5 on this page of APO’s website
  • Model the source spectra using model spectra from PHOENIX instead of blackbody models. For HAT-P-11 we use Teff = 4800 K, and for TRAPPIST-1 we use Teff = 2500 K , both with logg = 4.5 cm / s^2
  • Realized that we have to divide the output of synphot’s countrate() function by the gain of the modeled telescope
• There was some debugging we had to tackle to obtain the correct units/order of magnitude for the PHOENIX source spectra – the blackbody model is in units of 𝑒𝑟𝑔 𝑠−1 𝑐𝑚−2 𝐴˚−1 𝑠𝑟−1, while PHOENIX gives flux in 𝑒𝑟𝑔 𝑠−1 𝑐𝑚−3. I don’t think I fully understand yet, but the problem seems to be that while synphot handled the cm to angstrom conversion fine, the steradian was sort of lost in translation… The SourceSpectrum object was correct as long as we divided the normalized flux by pi.

With these factors implemented, our current precision looks like:

synphot TRAPPIST-1: 257K
actual TRAPPIST-1: 203K
synphot HAT-P-11: 30M
actual HAT-P-11: 34M

This week’s goals:

• Make a separate repo for notebook tutorials (maybe make a github “project” out of it?)
• Have no data files left in notebook (except CCD QE), get the needed data by querying instead
  • Eventually we will make a pull request to Astroquery to enable queries to the filter VO service for filter transmittance curves
  • In the meantime we will use this new functionality to query the SDSS filters for our count rate example
• Investigate using pwv_kpno to compute transmittance rather than using the Cerro Paranal model to further improve count rates.

Longer term goals:

• Make 4-5 notebooks which explore different use cases in order to get an idea of how we want to implement any changes or enhancements to synphot:
  1. Model spectrum -> Synthetic photometry
     • Example: existing APO notebook
     • (And maybe also Kepler?)
  2. Empirical spectrum (like from SDSS/Hubble website) -> Synthetic photometry
     • Example: Erik’s palomar spectrum + MDM Halpha observations
  3. Model spectrum -> synthetic spectroscopy
     • Example: Observations of a G dwarf with [the space-based mission Brett mentioned called CHEOPS, but don’t worry about that] at R~1k vs 100k – what count rates do you get?
  4. Empirical spectrum -> synthetic spectroscopy
     • Possible example: Some HII region spectrum -> how many hours to a S/N of X
• Implement a signal-to-noise predictor