# How Can I interpret this particular light curve without reading data on the side

There is only one dip in flux recorded. How can I interpret this particular light curve and find planetary radius

https://exo.mast.stsci.edu/exomast_planet.html?planet=55Cnce

– uhoh
Commented Aug 3, 2020 at 6:31
• I thought you might enjoy these links to your planet of interest. The first is a beta product so it's still in development but it has nice info: exoplanetarchive.ipac.caltech.edu/overview/55%20Cnc%20e The most detailed info is on the official ExoPlanet DB but it doesn't give a link to your planet, this is link is to the main search page. Enter your planet info "55 Cnc e" in the search box where it says "Explore the archive" so see all of the info known about this system and a list of all papers published about it: exoplanetarchive.ipac.caltech.edu/index.html Commented Aug 3, 2020 at 17:11

The radius of the planet is 0.17% of Jupiter's radius. Under the "Planet" info on the left, it says $$R_P$$ which is the radius of planet, and since the units are shown as $$[R_J]$$ this is the value is in comparison to Jupiter. It also gives the $$M_P$$ (mass of planet) in relation to $$M_J$$ (mass of Jupiter) as well.

The interesting thing here is the size of the star - it's smaller than our Sun.

To get the radius of the planet, find the radius of Jupiter and multiply it by 0.17.

A "year" on that planet is shorter than one of our days and it's orbiting extremely close to its host star, as well. The distance is given as 0.015 AU (astronomical unit which is the distance from the Earth to the Sun).

• +1 There are two ways to get subscripts; one is using MathJax as I've done here, and the other is to write something like R<sub>J</sub> where the first one turns subscript "on" and the second turns it "off". For superscripts its <sup></sup> and for strikethrough it's <s></s> and I'm sure there are more. To make these grayed out areas that show literally and aren't interpreted, use a backtick before and after.
– uhoh
Commented Aug 3, 2020 at 6:27
• @uhoh Thank you, I've been wondering how to do that! My answer looks much better after you fixed it. Commented Aug 3, 2020 at 16:44

There is only one dip in flux recorded.

No, it seems to be a folded light curve that may include of the order of a thousand cycles, must include at least a few cycles since the uncertainty given for the period on that page is roughly one part per thousand since a period is given:

Period [day]:             0.736539 ± 8.7e-4   Demory et al. 2016
Transit Duration [hour]:  1.5792   ± 0.0312   Winn et al. 2011


There is a sidebar on the left edge of the page that pops out with lots of bits of information and citations for each. If you hover over the description of each data field the citation appears.

How can I interpret this particular light curve and find planetary radius

Someone else will have to answer that, but in addition to the radius they also give the size of the orbit and the diameter of the star:

Rp [Rj]    0.17 ±0.01
Rs [R☉]:   0.94
a  [AU]:   0.015


• To clear up one small detail, the uncertainty isn't in the order of one part per thousand because thousands of cycles have been observed, it's tied to how shallow the transit is. This is an extremely shallow event and additional observations (with our current technology) won't reduce the uncertainty by much, if any. Deep transits like a huge hot Jupiter in front of a small dwarf star can be observed once or twice and have uncertainties even less than that since the difference in magnitude (the depth of the dip) is much larger. Commented Aug 3, 2020 at 20:16
• @AstroShannon Thanks! I've made an edit for now and I'll think about this further. I'd made several assumptions there that don't really apply. For a weak, noisy sinusoid sampled regularly during a single continuous run, some sentence similar to that might be defensible, but that abstract scenario is not anything like this.
– uhoh
Commented Aug 4, 2020 at 0:43