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I mean those kind of stars should be very stable and barely have activity.

Their light curves should be very very flat.

Our sun, as a G type star, are not so stable. At lest there are lots of floating solar spots.

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2 Answers 2

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Hipparchos numbers of the 26 most stable stars known: 2021, 2854, 5542, 16611, 19747, 24927, 32537, 38414, 42913, 45556, 50191, 57363, 71053, 73555, 74666, 76440, 74946, 90139, 94648, 96052, 10239, 102488, 104732, 111169, 116631, 118322.

Compare Hpmax and Hpmin: They differ 0.01. Standard error e_Hpmag is 0.0003 mag. There are 681 stars in the Hipparchos catalog with an amplitude of 0.01 mag.

More detail in this paper, including a link to the appropriate VizieR query.

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  • $\begingroup$ is there any special usage of there kind of stars except as photometric standard stars? $\endgroup$ May 3, 2014 at 2:52
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    $\begingroup$ @questionhang My first application would be to use them as instrument calibration, too. It's not self-evident, that they are of low variability almost all their life-time. But if so, the smaller of them would be better-suited for habitable planets, since they wouldn't change their habitable zone for a long time, and wouldn't cause short-time hazards for their planets by flares or pulsation. $\endgroup$
    – Gerald
    May 4, 2014 at 1:12
  • $\begingroup$ Maybe we can study why stars are so inactive and the smallest variability amplitude. The stars in the paper above still have a large variability scale(0.01 Mag). We can find more in Kepler data? $\endgroup$ May 18, 2014 at 8:29
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    $\begingroup$ The Sun is more stable than this - it's luminosity changes by a lot less than 0.01 mag on the same timescales surveyed by Hipparcos. $\endgroup$
    – ProfRob
    Apr 22, 2015 at 11:39
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You need to specify on what timescales and at what wavelengths to get a proper answer.

Despite your question, the Sun does appear to be a very stable star indeed. The luminosity changes over the solar cycle are about 0.1% (or 0.001 magnitudes) and even the biggest sunspots modulate the light by a fraction of one percent.

If you wanted to find stars more "stable" than this, the key is to find stars with lower levels of magnetic activity. For solar-type stars this means you have to find slower rotating objects which, because angular momentum is lost as stars get older, means you need to look for older stars.

K- and M-dwarfs have longer spin-down timescales and can remain active to much older ages, therefore I would not think these would generally be less active/less variable.

My recommendation would therefore be to look at old, population II halo F/G-type stars. As long as they are not in binary systems (which can influence the angular momentum evolution), then these ought to be the least magnetically active stars and the least variable (in principle).

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  • $\begingroup$ so statistically, younger stars should rotate faster and high level magnetic activities? But I know M&K stars are more magnetically active. Also, age-activity relation is not necessarily true for a single star. $\endgroup$ Apr 22, 2015 at 14:27
  • $\begingroup$ @Questionhang Yes, K and M dwarfs are more active at the same age, which is why I did not suggest these are more stable. The age-activity relationship is valid for single stars. What makes you say it is not? $\endgroup$
    – ProfRob
    Apr 22, 2015 at 14:44
  • $\begingroup$ @ faster rotation means younger and more magnetic activities? But M&K are old. Besides, that age-magnetic relation should not be strictly followed by all the stars. $\endgroup$ Apr 22, 2015 at 14:54
  • $\begingroup$ @questionhang - You are talking to an expert in determining the ages of stars through activity-age and activity-rotation relations. (e.g. adsabs.harvard.edu/abs/2014EAS....65..289J ). Activity is not solely connected with age, it is also a function of mass and convection zone thickness and is not followed by close binary systems. Even old M dwarfs could be much more active than the Sun. Thus I do not think that, older K and M dwarfs will be much less variable than the Sun. $\endgroup$
    – ProfRob
    Apr 22, 2015 at 16:12
  • $\begingroup$ I admit old stars are active. But how about younger stars? They rotate faster, so there are more activities caused by magnetic field? $\endgroup$ Apr 23, 2015 at 1:56

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