# Tag Info

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The density of stars in the solar neighbourhood is about 0.003 stars per cubic light year. Therefore at any one time you might expect only around 30 to be within 13 light years of the Sun. However, stars are moving with respect to each other. These relative motions are of order 10-100 km/s, which translates to about 30-300 light years/million years. ...

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The criteria for sample selection are admittedly not made overly clear in the preprint itself (Wysoczańska et al.). It appears that the authors started with a list based on stars that were previously believed to have come close to the Sun at some point in the past or future. That list was then augmented based on data from Gaia's second data release, to get a ...

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The closest service to what you are describing is the SIMBAD Astronomical Database from the Université de Strasbourg/CNRS. At the time I write this post, it contains 10.8M objects and 35.5M identifiers. It does not have a single CSV you can download with this information (to the best of my knowledge, and I've asked), but there is an API and TAP service ...

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TL;DR: Turn Off point (TO) means the location of the "knee" in the HRD of clusters of stars. TAMS is an imaginary line in the HRD that is defined by the location of stars of different mass at the end of hydrogen burning. It constitutes the upper boundary of the main sequence. More details: There maybe some confusion because the terms are not completely ...

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Schindler, Green & Arnett (2015) "Exploring Stellar Evolution Models of sdB Stars using MESA" provide several evolutionary tracks and lifetimes for sdB stars. The canonical timescale for the sdB lifetime is about 100 Myr (Dorman et al. 1993; Charpinet et al. 2000). We calculated sdB lifetimes of approximately 140–170 Myr for Mini = 1.0 M⊙ (...

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Whether convection exists depends on whether the interior radiative temperature gradient reaches the adiabatic temperature gradient. The interior radiative temperature gradient is proportional to the opacity and the outward energy flux, and inversely proportional to $T^4$. As the star evolves on the main sequence, the central temperature goes up and the ...

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In section 3 of this paper on the possible origin of two planets orbiting a B-type subdwarf, called KIC 05807616, and of which I asked a question a while ago, the survivability of the planets to the intense UV radiation of their host star is examined. Here is an excerpt from the summary: In section 3 we examined the survivability of the planets to ...

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The first stars after the big bang would have contained hydrogen and not much else. As they age heavier elements are created within. That's how elements are created. Well, up as far as iron at least. Beyond that you need a supernova to happen. This is all assuming that I'm remembering my A-level physics accurately. It's been a while.

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Yes, it is possible for stars to exist that contain basically no hydrogen and helium - they are abundant and they are called white dwarfs. Rarer examples are the sdB and sdO stars that are composed almost entirely of helium. However, white dwarf "stars" are not undergoing fusion processes - they are inert. This illustrates fundamental physics. There is ...

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We would have $$\tau = d/0.99c - d/c,$$ of warning, where $d$ is the distance to the star when we first detect its light and $c$ is the speed of light. Would we see it - yes indeed. Since $$\lambda_{\rm obs} = \lambda_0 \left( \frac{1 - v/c}{1+ v/c}\right)^{1/2},$$ the light from the star would be blueshifted by a factor of 14, so for a solar type star, ...

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Formation of pure hydrogen stars is not likely to have happened in this universe, because Big Bang nucleosynthesis resulted in the production of helium and lithium (plus the unstable isotopes tritium and beryllium-7, which decay into helium-3 and lithium-7 respectively) in addition to hydrogen. It is therefore likely that the initial star-forming ...

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Processes energetic enough to accelerate a star to 99% of the speed of light are not known. A close interaction and ejection from a multiple black hole system could perhaps provide enough energy, but such close interaction with black holes would probably rip the star apart before it could reach such excessive speeds. Hypervelocity stars are known. They have ...

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Yes, a star can exist that's entirely hydrogen. Hydrogen is the fuel that makes stars happen unless they're very large. A star made entirely of hydrogen, so long as it was massive enough, would be very similar to the stars we see. The "metalicity" which refers to non hydrogen-helium elements has some effect on the star's rate of fusion, density and ...

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Stars are formed from the thin gas in space, and the thin gas in space is made of roughly 3/4 Hydrogen and 1/4 Helium (+trace amounts of other elements). There's no way to get a star made of 100% Oxygen as there is no way to gather enough oxygen in one place to get sufficient mass to make a star. So all real stars will be made mostly of H and He, with small ...

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According to Ginsburg, Loeb & Wegner (2012) "Hypervelocity planets and transits around hypervelocity stars", planet-hosting hypervelocity stars could form from the disruption of a stellar binary by a massive black hole, and the probability that the planet remains bound to the hypervelocity star is fairly high for suitable initial conditions. In their ...

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You can check whether the star is anti-circumpolar i.e. if it never rises above the horizon (if its upper culmination altitude is less than zero). If it is, you will never see it from that location. If it is not, at some point during the year you will be able to see it in conditions with minimal light pollution if its upper culmination altitude is around ...

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The HR diagram is a plot of luminosity (or a proxy) versus temperature (or a proxy). $B-V$ is a proxy related to temperature, therefore to plot your point on a 2-d plot you obviously need the other axis information - the luminosity, or its proxy the absolute magnitude. This in turn needs an apparent magnitude and a distance to the star. It is also possible ...

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For that particular value, there are at least two branches the star could correspond to, it could for instance be a subgiant or on the main sequence (as you can see here), so you cannot unambiguously determine its absolute magnitude/luminosity just from its B-V colour. However, the Wikipedia article for 33 Psc gives some information about it : https://en....

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The "radius" of the Sun is basically where the optical depth to radiation at any particular wavelength is about 1 (or some times 2/3 is used). This is known as the photosphere and is from where the light that we measure comes from. The "thickness" of the photosphere - i.e. the depth over which the optical depth changes from being negligible to very large is ...

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