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F - type stars

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F - type star HZ

F - type stars are yellow - white warmer equivalents to our sun, Sol. They have a large Habitable Zone, that can support multiple planets. Their luminosity is stronger, their mass is slightly larger then Sol, but also the solar wind is more powerful.

The star Edit

The most known F - type star is Procyon. These kind of stars are more rare in the Universe then G - type stars like Sol and far more rare then K - type stars. Their surface temperature is of 6000 ... 7600 K.

Luminosity is up to some point similar to that of Sol, containing infrared, ultraviolet and visible light. The output of ultraviolet light is higher, so an ozone layer is needed. The star generates a lot of light in visible spectra, but it produces more blue light then red. The infrared emission is also present. Solar winds are stronger then what sol generates. Around such a star, solar flares are not a so important, compared to this continuous solar blow.

F - class stars have a shorter lifetime then Sol and gradually transform into red giants, before ending into a white dwarf. This is not a problem compared with the life of a human settler. What is important is that settlers can find these stars in different stages of their existence. One star might be following main sequence, while another one is starting to fuse helium and slowly becoming a red giant. These transformations have strong effects on hosted planets.

Hosted planet Edit

Planets have been discovered around F - type stars, like the one found around Tau Bootis. These stars can develop planetary systems similar to Solar System.

Distance and orbit: A planet in the center of Habitable Zone must be located around 1.5 AU from hosting star. A model planet around Procyon would be located at the same distance where is Mars in Solar System. ISDB plots a planet in its habitable zone at 2.74 AU, so even further away. That planet will experiment an orbital period of 3.4 Earth years. What would Earth look like if placed in this orbit around Procyon? First of all, the seasons will be very long, with summers and winters of nearly an year. Some plants will adapt to this, some will not. Facing a winter that lasts for 300 Earth days, animals (and probably also humans) would like to migrate to warmer places, returning back in summer. Arctic plants, that face 6 months of harsh winter, would be easy to adapt.

Tidal forces are small (below 10% of what Sol causes to Earth), so that rotation period should be small enough to create an Earth-like day-night cycle. Lower gravity means that the gravity sphere surrounding a planet is larger, so there is a higher chance for satellites to exist. With a satellite and a high rotation period, there is a higher chance that the planet has a strong internal dynamo to power a magnetic field. On the other hand, solar wind is much stronger, so that the dynamo will have to face more powerful forces.

Extended habitable zone can be marked by using some technology. By using greenhouse gases, colder planets can be warmed enough to sustain Earth-like life forms. Strong greenhouse gases can use very dim light, but would plants survive? Plants can live on with a luminosity of 0.1% of that found on Earth, if it contains an equilibrium of red and blue light, just like what is radiated from sol. F - type stars generate blue light in similar percents like Sol, but less red light (around 60%). This is not such a big difference. In Solar System, plants can survive up to the orbit of Neptune, around 30 times further away then Earth. For Procyon, the distance where light is similar to the orbit of Neptune, is 80 AU. Because of the lack in red light, the outer limit for Earth-like plants is around 70 AU, somewhere in Kuiper Belt, compared to Solar System). Usually, F - type stars rotate faster, so they have a stronger magnetic field then Sol. The more stronger solar wind keeps interstellar medium further away. Terraformed planets will not be outside of protection from interstellar charged particles.

Inner, warmer planets, can be cooled with the help of similar methods described for Mercury or Venus, but there is a problem. The stronger ultraviolet emission and powerful solar wind can affect shielding layers and a brake in the shield will have bad consequences for local ecology.

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