First light curve parser

[bmorris3]

This PR implements a first crack at the light curve parser.

If you have a local Kepler FITS data product (or can download one from MAST), you can load it into LCviz with:

from lightkurve import search_lightcurve
from lcviz import LCviz

light_curve = search_lightcurve(
    "HAT-P-11", mission="Kepler", cadence="long", quarter=10
).download()

lcviz = LCviz()

# # Optionally normalize the light curve:
# light_curve = light_curve.normalize()

lcviz.load_data(light_curve)
lcviz.show()

I've made the x label show the time since the start of the reference data, and it defaults to units of seconds (the WCS default, I think?), and the y label shows units of "Flux" for count rates, and "Relative flux" for dimensionless light curves.

I've written some tests that I had anticipated would fail because of lightkurve/lightkurve#1299, but it looks like that error may have been a mirage from a mismatch of the astropy and lightkurve versions (still investigating).

[codecov]

Codecov Report

Patch coverage: 79.24% and project coverage change: -4.33 ⚠️

Comparison is base (909ed65) 91.82% compared to head (96c1d12) 87.50%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #10      +/-   ##
==========================================
- Coverage   91.82%   87.50%   -4.33%     
==========================================
  Files           9        9              
  Lines         159      192      +33     
==========================================
+ Hits          146      168      +22     
- Misses         13       24      +11     

Impacted Files	Coverage Δ
lcviz/parsers.py	67.85% <65.38%> (-32.15%)	⬇️
lcviz/viewers.py	94.59% <90.47%> (-5.41%)	⬇️
lcviz/conftest.py	91.66% <100.00%> (+0.75%)	⬆️
lcviz/helper.py	100.00% <100.00%> (ø)

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[kecnry]

Not sure how I feel about the time since reference thing... we'll likely eventually want options for that in a plugin somewhere... but works for now! Thanks!

[bmorris3]

Not sure how I feel about the time since reference thing...

I agree it's not perfect. I usually prefer to plot my transiting exoplanet LCs in units of BJD - <some number>, like this. In general of course, LCs can span only a few seconds, or many years, so having unit options other than seconds would be great.

we'll likely eventually want options for that in a plugin somewhere...

Agreed. This might require a bit of work. I'm using the ndcube TimeTableCoordinate to convert Time objects into gwcs representations of the time axis. TimeTableCoordinate defaults to units of seconds, I think because the WCS TIME spec expects seconds. More to look into there.

[bmorris3]

With approval from @kecnry, I'll merge now and make a ticket to follow-up when lightkurve/lightkurve#1299 is addressed. Thanks!