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6

Here is the very study you are looking for by Bailer-Jones (2014). Using the re-reduction of the Hipparcos astrometry, he has integrated orbits for 50,000 stars to look for objects that might come or might have come close to the Sun. The K-dwarf Hip 85605 is the winner on that timescale, with a "90% probability of coming between 0.04 and 0.20pc between ...


4

Saturn is the most oblate planet in the solar system. If the equatorial diameter is $a$ and the polar diameter is $b$ then its oblateness, $(a-b)/a = 0.1$. We do not know the oblateness values for more than one or two exoplanets and even these are somewhat uncertain, but are thought to be lower than Saturn's value. For example ...


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Someone suggested this object to be 31 Ori. After further research, equipped with the name, I confirmed this object to be 31 Ori. Source of confirmation: http://www.astrostudio.org/xhip.php?hip=25737


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The actual answer has nothing at all to do with the temperature. Even low-mass stars would form black holes if they ran out of nuclear fuel to burn, and simply cooled whilst being supported by "standard" gas pressure in their centres. That is because that gas pressure would be proportional to the temperature, but the star is able to cool so it would need ...


2

Here's how parallax works. You measure the position of a star in a field of stars that are (presumably) much further way. You do this twice, separated by 6 months. You then calculate the angle that the star has moved against its background stars. This angle forms part of a large triangle, with a base that is equal to the diameter of the Earth's orbit around ...


1

There really isn't anything as comprehensive as you want. And, we don't have accurate information for all of these variables for a large number of stars. The two main problems are masses and radii. Really the only set of stars that have both measured masses and radii are those in eclipsing binary systems. If these binary stars also have distances, measured ...


1

Most stars are of a solar-mass or below. The average number of companions that each stars has (in the sense of being part of binary or higher multiple systems) systems ranges from 0.75 for stars of a solar mass to approximately 0.35 (not a well-established number) for the more numerous M-dwarfs. Let's take a compromise value, say 0.5. The separation ...


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Most of the universe is pretty empty in terms of the density you're used to in daily life. It's perhaps not that stars are far apart, but that they are pretty compact. This is because baryonic matter (as opposed to dark matter) can lose energy via electromagnetic radiation and hence condense to smaller and denser objects. This is only opposed by angular ...


1

The dwarf planet Haumea two equatorial diameters, it is triaxial. The longest equatorial diameter is about twice the length of the polar diameter. According to Google and Wikipedia, the most oblate star is Achernar which has an equatorial diameter 56% larger than the polar diameter due to it rapid spin. The discussion at ...


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I think it is going to depend on the type of object being examined. Planetary objects tend to be more spherical than stars, which in turn tend to be more spherical than galaxies. My vote goes toward the Heliospheric current sheet, which is thought to extend 10-20 astronomical units (about 1.5x10^9km to 3x10^10km) from the Sun, and is thought to be about ...


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just check what 'median' means. the median stellar mass is such that half of all stars have lower and the other half hihger mass. it has nothing to do with the logarithm. I havn't seen the term (median stellar mass) in the scientific literature. Looking at the paper you're referring to, they never use the expression "median stellar mass". Moreover, this ...


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There have of course been extensive observations of clusters of stars. To all intents and purposes, to the limits of experimental accuracy, it looks like stars that are born in the same open cluster or star-forming region are all born with the same composition. e.g. http://adsabs.harvard.edu/abs/2014A%26A...567A..55S , ...


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For me, the best and most reliable source of absolute magnitudes and spectral types is the book Allen's astrophysical quantities. Chapter 15, called Normal Stars, contains spectral types, absolute magnitudes, colors and effective temperatures for main sequence, giant and supergiant stars. The references are at the end of the chapter. HTH, Germán.


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The spectra of a red giant and a red dwarf are completely different, so there isn't really too much to say about this. For example, alkali lines are almost non-existent in red giants, but strong in red dwarfs. The theory as to why this happens is the stuff of a standard graduate/undergraduate course on stellar atmospheres, not an SE answer. The fact is that ...



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