Quote from: Star One on 03/13/2017 03:53 pmQuote from: Ben the Space Brit on 03/13/2017 03:39 pmThat's class-M dwarves for you: Once they hit main sequence, there's really no way to easily tell the difference between 100 million or 10 billion years old!From my limited understanding of that article it's the radiation output that's proving contradictory ageing wise.It's worse than that. I think that article references the 1.4 day stellar rotation period from Nature. But the actual rotation period is more like 3.3 days.So that is contradictory as well, indicating a much older star (>= ~1bn). However, gyrochronology is poorly constrained for M dwarfs.--- Tony
Quote from: Ben the Space Brit on 03/13/2017 03:39 pmThat's class-M dwarves for you: Once they hit main sequence, there's really no way to easily tell the difference between 100 million or 10 billion years old!From my limited understanding of that article it's the radiation output that's proving contradictory ageing wise.
That's class-M dwarves for you: Once they hit main sequence, there's really no way to easily tell the difference between 100 million or 10 billion years old!
Don't stars slow down as that get older or does that only apply to ones like our Sun?
If I understand correctly, the problem is that the different indicators are giving different age ranges for TRAPPIST-1. This would indicate either the existing theoretical models are wrong or (and this is probably more likely) TRAPPIST-1 is an anomalous body and we can't take anything about it for granted based on analysis of other M8s.
Quote from: Ben the Space Brit on 03/13/2017 04:39 pmIf I understand correctly, the problem is that the different indicators are giving different age ranges for TRAPPIST-1. This would indicate either the existing theoretical models are wrong or (and this is probably more likely) TRAPPIST-1 is an anomalous body and we can't take anything about it for granted based on analysis of other M8s.Could it be because it's just on the line to being a brown dwarf.
Perhaps and I don't know if this is a possibility that it started off as a brown dwarf but somehow crossed the boundary into being a red dwarf at a later point?
Quote from: Star One on 03/13/2017 04:46 pmQuote from: Ben the Space Brit on 03/13/2017 04:39 pmIf I understand correctly, the problem is that the different indicators are giving different age ranges for TRAPPIST-1. This would indicate either the existing theoretical models are wrong or (and this is probably more likely) TRAPPIST-1 is an anomalous body and we can't take anything about it for granted based on analysis of other M8s.Could it be because it's just on the line to being a brown dwarf.My understanding is that although astronomers think it is a very low-mass star rather than a brown dwarf, this is by no means certain and it could actually be a brown dwarf. It's very difficult to distinguish between a very low-mass star and a young brown dwarf.QuotePerhaps and I don't know if this is a possibility that it started off as a brown dwarf but somehow crossed the boundary into being a red dwarf at a later point?It would've had to have absorbed sufficient additional mass at some point after formation - preferably hydrogen, but most kinds of mass would do (how much mass would depend on how close the brown dwarf was to being a red dwarf!). One possibility is that a hot Jupiter spiraled in too close and crashed into the brown dwarf, the current exoplanets forming after this event.
The TRAPPIST-1 system is the first transiting planet system found orbiting an ultra-cool dwarf star. At least seven planets similar to Earth in radius and in mass were previously found to transit this host star. Subsequently, TRAPPIST-1 was observed as part of the K2 mission and, with these new data, we report the measurement of an 18.764 d orbital period for the outermost planet, TRAPPIST-1h, which was unconstrained until now. This value matches our theoretical expectations based on Laplace relations and places TRAPPIST-1h as the seventh member of a complex chain, with three-body resonances linking every member. We find that TRAPPIST-1h has a radius of 0.715 Earth radii and an equilibrium temperature of 169 K, placing it at the snow line. We have also measured the rotational period of the star at 3.3 d and detected a number of flares consistent with an active, middle-aged, late M dwarf.
We have also measured the rotational period of the star at 3.3 d and detected a number of flares consistent with an active, middle-aged, late M dwarf.
Quote from: Star One on 03/14/2017 08:36 amWe have also measured the rotational period of the star at 3.3 d and detected a number of flares consistent with an active, middle-aged, late M dwarf.So how old is an active, middle-aged, late M dwarf?
While the long spin-down times of ultra-cool dwarfs prevent derivation of a robust gyrochronology relation, the rotationalperiod of TRAPPIST-1 is roughly in the middle of the period distribution of nearby late M dwarfs, suggesting an age in the range3−8 Gyr based on a star formation history that declines slightly with time.
... suggesting an age in the range 3−8 Gyr based on a star formation history that declines slightly with time.
Quote from: as58 on 03/14/2017 05:01 pm... suggesting an age in the range 3−8 Gyr based on a star formation history that declines slightly with time.Assuming Gyr means Gigayear, or 1 billion years, then the Trappist star is 3-8 billion years old, which is the same "range" as Sol, which is 4.55 billion years old. Do I have that right?
Now, Lingam and Loeb have calculated that exact probability. Comparing the TRAPPIST-1 planets to Earth and Mars, they found that the travel time between one planet and the next is shorter by a factor of a hundred. This boosts the chance that life can survive such a harrowing journey. They also found that the likelihood of one planet’s debris landing on another is larger by a factor of 20 or so.Altogether, the possibility that life can play hopscotch from one planet to the next is a few thousand times higher among the TRAPPIST-1 worlds than the possibility that it did the same from Mars to Earth.
I sometimes wonder how many of the stars in the locality came out of the same stellar nursery as our sun.
Quote from: Star One on 03/14/2017 08:50 pmI sometimes wonder how many of the stars in the locality came out of the same stellar nursery as our sun.It's a good question: there are several searches looking for "solar twins" ... from memory, we've found a few candidates but not many.But Trappist-1 is not one of them ... its relative velocity is too high for it to be a close neighbour for long. Again from memory, its velocity puts it on the YD/OD boundary.--- Tony
Quote from: jebbo on 03/27/2017 03:26 pmQuote from: Star One on 03/14/2017 08:50 pmI sometimes wonder how many of the stars in the locality came out of the same stellar nursery as our sun.It's a good question: there are several searches looking for "solar twins" ... from memory, we've found a few candidates but not many.But Trappist-1 is not one of them ... its relative velocity is too high for it to be a close neighbour for long. Again from memory, its velocity puts it on the YD/OD boundary.--- TonyForgive my ignorance Tony but what is the YD/OD boundary?
Quote from: clongton on 03/27/2017 10:33 pmQuote from: jebbo on 03/27/2017 03:26 pmQuote from: Star One on 03/14/2017 08:50 pmI sometimes wonder how many of the stars in the locality came out of the same stellar nursery as our sun.It's a good question: there are several searches looking for "solar twins" ... from memory, we've found a few candidates but not many.But Trappist-1 is not one of them ... its relative velocity is too high for it to be a close neighbour for long. Again from memory, its velocity puts it on the YD/OD boundary.--- TonyForgive my ignorance Tony but what is the YD/OD boundary?I was wondering that as well TBH.
young disk/old disk? Though they're more commonly called thin and thick disks.
We analyze short cadence K2 light curve of the TRAPPIST-1 system. Fourier analysis of the data suggests Prot=3.295±0.003 days. The light curve shows several flares, of which we analyzed 42 events, these have integrated flare energies of 1.26×1030−1.24×1033 ergs. Approximately 12% of the flares were complex, multi-peaked eruptions. The flaring and the possible rotational modulation shows no obvious correlation. The flaring activity of TRAPPIST-1 probably continuously alters the atmospheres of the orbiting exoplanets, making these less favorable for hosting life.