<p>FU Orionis episodes (for that is what they are, rather than a particular 'type' of star) happen due to large infall of material from the circumstellar disc. They appear to be a normal stage in the formation of low-mass stars. We know of so few FUORs because the FU Ori episodes happen on widely-spaced timescales of several thousand, or several million, years. So it's not that they are especially rare - it's just that we don't live long enough to see many!</p>

CC BY-SA 4.0
2020-12-14T14:56:30.853Z
If it were once every several millon years then each PMS star might have one episode and they woul dbe extremely rare indeed. Once every few thousand years is more likely.
ProfRob
CC BY-SA 4.0
2020-12-15T19:52:27.347Z
Sure, but I didn't mean this terribly literally, just intended to point out that, on human timescales, they are very rare events.
Michael Poxon
CC BY-SA 4.0
2020-12-14T13:50:19.470Z
2020-12-14T13:50:19.470Z
Michael Poxon
<p><a href="https://en.wikipedia.org/wiki/FU_Orionis_star" rel="nofollow noreferrer">FU Orionis</a> variables are protostars that go through massive outbursts that drastically change the star's spectral type and magnitude. With the star <a href="https://en.wikipedia.org/wiki/V1057_Cygni" rel="nofollow noreferrer">V1057 Cygni</a>, this star was known to go from a K type dwarf star (K V) to an F-type supergiant, according to Wikipedia. In 2016, a study showed that this star had a companion. So does this change any property (age, reason for eruption) of this star, and why did this FUor have such a massive change in luminosity?</p>

CC BY-SA 4.0
2020-12-12T14:23:41.297Z
I don;t understand the question. Are you arguing that V1057 Cyg is not, or is some way not typical of an FU Ori star? The explanation for FU Ori outbursts is given in the short wikipedia pages you link to. FU Ori is also a binary and brightened by nearly 7 magnitudes in the 1930s.
ProfRob
<star><variable-star><protostar><fu-orionis>
How is V1057 Cygni supposed to go from K type dwarf to F type giant?
WarpPrime
# How is V1057 Cygni supposed to go from K type dwarf to F type giant?

(Asked by: username_0 on 2020-12-12)

[FU Orionis](https://en.wikipedia.org/wiki/FU_Orionis_star) variables are protostars that go through massive outbursts that drastically change the star's spectral type and magnitude. With the star [V1057 Cygni](https://en.wikipedia.org/wiki/V1057_Cygni), this star was known to go from a K type dwarf star (K V) to an F-type supergiant, according to Wikipedia. In 2016, a study showed that this star had a companion. So does this change any property (age, reason for eruption) of this star, and why did this FUor have such a massive change in luminosity?

**Tags:** star, variable-star, protostar, fu-orionis
> **Comments:**
> **username_1**: I don;t understand the question. Are you arguing that V1057 Cyg is not, or is some way not typical of an FU Ori star? The explanation for FU Ori outbursts is given in the short wikipedia pages you link to. FU Ori is also a binary and brightened by nearly 7 magnitudes in the 1930s.  

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## 1 answers

### Answer by username_2 on 2020-12-14. Score: 1

FU Orionis episodes (for that is what they are, rather than a particular 'type' of star) happen due to large infall of material from the circumstellar disc. They appear to be a normal stage in the formation of low-mass stars. We know of so few FUORs because the FU Ori episodes happen on widely-spaced timescales of several thousand, or several million, years. So it's not that they are especially rare - it's just that we don't live long enough to see many!

> **Comments:**
> **username_1**: If it were once every several millon years then each PMS star might have one episode and they woul dbe extremely rare indeed. Once every few thousand years is more likely.  
> **username_2**: Sure, but I didn't mean this terribly literally, just intended to point out that, on human timescales, they are very rare events.  

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