All sky map of exoplanet host stars: Surveys (exoplanet.eu)

There are many different surveys looking for new extra-solar planets. Right now the most successful technique is the transit method and there are many programs using this method. In this all sky map I was trying to show a few of these surveys which look at many stars, monitor their brightness, and try to find exoplanets in the stars' light curves.

Probably the most well-know survey is Kepler; it's the instrument that found the most planets until now. However, it looked at a very limited area of the sky. You can see it on the left side of the map where the large number of black dots are.

CoRoT was another space-based mission which was very successful; however, it did not nearly find as many exoplanets as Kepler. Its observing strategy was a bit different. CoRoT did not stare at one area in the sky all the time but switched its field of view every half year. One time it looked in the direction of the center of the Milky Way, which are the purple squares on the left side, and the next time it looked at an area in the opposite direction. These so-called 'anti-center' runs can be seen in the center of the map.

Also very successful is WASP. The nice thing about this survey is that (1) it observes from the ground and (2) it looks (almost) everywhere in the sky. The 104 planets I got from exoplanet.eu (including SuperWASP) are really quite a number.

There are lots of different missions listed in the legend of the map and I do not want to go into detail on everyone of them. It is not a complete list of programs but rather what I could made out of the information provided by exoplanet.eu. Unfortunately, it is kinda hard to find which planet was detected by which survey because this is not listed there. So the host stars (and planets) I plot here are named after the program they were found with - and this way I could plot them. However, this is not true for every planet found and also not true for every survey.

This is especially disappointing for the planets found with the RV method. I would have liked to plot all the RV planets coming from, e.g., HARPS, which is an amazingly successful instrument, but I could not easily collect the necessary information. The host stars usually keep their name because they are bright, well-known objects (with HD or HR numbers). So it's not possible for me to get the survey from the name alone.

After all, this map is supposed to give an impression of which transit surveys there are and how they observe. It's not meant to be complete. Furthermore, the detection method listed in the database is not always 'transit'. This is because some systems are re-observed in RV to get the mass of the planet. Others, e.g., OGLE are no transit survey, although they do observe light curves. It can by chance also find transits but OGLE is actually looking for the signatures of microlensing events.

All sky map of exoplanet host stars: Multi-planet systems (exoplanet.eu)

With this post I continue my series on exoplanet host star all sky maps. What you see is basically the same thing I showed two posts ago. This time, however, I choose the color to represent the number of exoplanets in the system. So the symbol tells you which method was used to detect the system and the color tells you how many planets are know right now in this system (August 3, 2015, exoplanet.eu). The 740 lightyellow-colored host stars have only one planet, the one black circle in the Kepler field of view (Kepler-90 alias KOI-351) is the only exoplanet system with seven planets - all transiting the host star.

The Kepler field of view is so crowded that I include a zoom in on this region; it's the figure on the left side. The only seven planet system is on the top right of the Kepler FOV whereas the only transiting six planet system (Kepler-11) is pretty much at the bottom. In the all sky map you can see three other six planet systems, however, these where detected with the RV method.

Exoplanet host stars: The Kepler field of view (exoplanet.eu)

This is an addition to the post before. The plot shows the Kepler field of view in detail, all symbols and colors stay the same. This is the region in the sky from which we - by far - know the most planets around stars. Until July 23, 2015, Kepler has discovered 1879 confirmed exoplanets around 471 stars (according to exoplanetarchive.ipac.caltech.edu).

All sky map of exoplanet host stars (exoplanet.eu)

Today I'd like to show something not directly connected to the last couple of posts. This is an all sky map of exoplanet host stars. Different colors/symbols indicate the method used to detect the planet. The data was taken from exoplanet.eu. Actually, I tried to plot all planetary systems know today, which according to exoplanet.eu should be 1228, but for some reason I am missing three in the transit method.

The underlying magenta colored points are about one million stars from the Tycho catalog (ESA Hipparcos satellite). The map is an aitoff projection of the sky in galactic coordinates and the Milky Way lies at the equator; this is why most of the stars are located there.

Most of the planets are detected with the transit method. However, the majority is located in the small area crowded with black dots - the Kepler field of view. When we talk about statistics of transiting exoplanets we are actually talking about a small part in the sky and not the entire sky. Astrophysicists just assume that it should be the same everywhere. The other black dots come from different surveys, e.g., CoRoT or WASP.

The picture is different when looking at planets detected with the radial velocity (RV) method. They seem to be more uniformly distributed. It's the second most successful technique with 454 stars having planets around them.

At least according to exoplanet.eu, so far there is only one astrometry planet and it is very close to the Kepler FOV - although it's not in it. The star is HD 176051 b. So far it seems to be too difficult to detect planets with this method, but it is expected that with GAIA there will be many planets coming from this technique.

Imaging seems pretty much located to certain areas, avoiding the plane of the Milky Way as much as possible. This is probably a good idea since background stars that coincidentally stand close to the potential host stars make it more difficult to find planets - or might even be misinterpreted as bodies belonging to the system.

All microlensing planets come from a limited area in the direction of the center of the Milky Way, which in this map is at the edge. This illustrates nicely that microlensing really samples a quite different population of stars. All other techniques try to go away from the galactic center (and even the galactic plane) and only find exoplanets rather close to the Sun. The most distant microlensing planet, however, is about 25000 light years away - virtually in the center of the Milky Way.

The transit timing variation (TTV) planets are all in the Kepler FOV. For this method one needs good light curves and a long cadence to cover many transits, and this is what Kepler does best. According to exoplanet.eu there are only four TTV planets - which I do not think is true; there have to be much more. exoplanets.org says it's more like 60 (including some pulsar planets), which I believe is closer to the real number.

Finally, we have the planets around pulsars. There are a few in the Kepler FOV, but otherwise I do not really see a system there. I think it is nice to notice that PSR 1257 12 b is the star with the first exoplanet detection in the year 1992 - and it actually is a three-planet system! I think is has to be one of the two triangles in the upper right. Usually, people cite 51 Peg b as the first exoplanet - it was the first around a solar-type star. I guess pulsars are just too different ...