# How to use `lightkurve`

’s river plot function¶

When we are looking for periodic signals, sometimes it can be useful to see how they evolve overtime. You can do that using the `lightkurve`

method `plot_river`

on a `FoldedLightCurve`

object. Let’s look at how to do that now

```
[1]:
```

```
% load_ext autoreload
% autoreload 2
```

```
[2]:
```

```
import lightkurve as lk
```

The first thing we are going to do is download some data. We’ll use the target `KIC 6185476`

, which is also known as `KOI-227`

. This object exhibits strong Transit Timing Variations (TTVs), where the planet candidate changes its transit time, and is not exactly periodic.

We can use `lightkurve`

’s `search_lightcurvefile`

function to get all of the light curves from MAST and stitch them together.

```
[3]:
```

```
lc = lk.search_lightcurvefile('KIC 6185476').download_all().PDCSAP_FLUX.stitch()
```

```
[4]:
```

```
lc.plot()
```

```
[4]:
```

```
<matplotlib.axes._subplots.AxesSubplot at 0x12311aa58>
```

When we plot the data, we see that there is a long term trend, likely from starspots. We can remove this with a simple Savitzky-Golay filter using `lightkurve`

’s `flatten`

method.

```
[5]:
```

```
clc = lc.flatten(21)
clc.plot()
```

```
[5]:
```

```
<matplotlib.axes._subplots.AxesSubplot at 0x1231a3630>
```

The light curve is now flat, let’s fold the light curve and plot it.

```
[6]:
```

```
# Period and t0 from NASA Exoplanet Archive
p, t0 = 17.660114, 136.57258
```

```
[7]:
```

```
folded_lc = clc.fold(p, t0)
folded_lc.scatter()
```

```
[7]:
```

```
<matplotlib.axes._subplots.AxesSubplot at 0x127a37f60>
```

It looks like there is a concentration of points that are around phase of `0`

, but they don’t seem to line up nicely. Let’s use `river`

to plot the light curve in a more legible way.

```
[8]:
```

```
folded_lc.plot_river()
```

```
[8]:
```

```
<matplotlib.axes._subplots.AxesSubplot at 0x12b0532e8>
```

The river shows the same plot as the `fold`

method, but each time the light curve is folded, a new row is started in the plot. The colorbar then shows the flux in each part of the light curve.

In this case we see a beautiful trend as the planet candidate orbit changes. In some cases, the signal won’t be this obvious. We can also use the `river`

method to bin in time to increase the signal to noise in any bin.

```
[9]:
```

```
folded_lc.plot_river(bin_points=5, method='median')
```

```
[9]:
```

```
<matplotlib.axes._subplots.AxesSubplot at 0x12a911ef0>
```

Finally we can also use `plot_river`

to look at the folded light curve in terms of standard deviation. This is useful when looking for signals that are of high significance.

```
[10]:
```

```
folded_lc.plot_river(method='sigma', bin_points=1)
```

```
[10]:
```

```
<matplotlib.axes._subplots.AxesSubplot at 0x124634a20>
```

We see in the above river plot that there is a signal around phase zero (our planet candidate) that is always \(< -3\sigma\) from the mean, showing that it is a significant detection.