# Tag Info

## Hot answers tagged star

12

Nearly all the helium in the photosphere of the sun comes from the helium in the interstellar gas that collapsed to form the sun. That helium was produced shortly after the Big Bang (in about the first 20 minutes) while the universe was hot and dense enough for hydrogen to fuse to helium. That produces a universe in which ordinary matter is about 25% helium ...

12

It's neither the angular diameter or prallax precision that is the limiting factor, but the fact that it is difficult to get the interferometric measurements for faint stars. State-of-the-art angular diameters are measured by infrared interferometry (e.g. with the CHARA array - Gordon et al. 2019). The most precise measurements of angular diameters have an ...

7

K-type dwarfs behave like a solar mass star, and will leave behind a (slightly) lower mass white dwarf. F-type dwarfs will behave like a solar mass star and leave behind a (slightly) higher mass white dwarf. Higher mass (hotter) stars will produce higher mass white dwarfs, up until the initial main sequence star is of about $8M_{\odot}$ (a spectral type of ...

6

I'm assuming you're talking about physical distances (as opposed to any of the other distance measures in cosmology). The comoving distance to a galaxy at redshift $z$ is $$d_C(z) = \frac{c}{H_0}\int_0^z \frac{dz}{\sqrt{ \Omega_r(1+z)^4 + \Omega_m(1+z)^3 + \Omega_k(1+z)^2 + \Omega_\Lambda }},$$ ...

3

The parallax is always easier to measure than the angular size of any planet. This is also true for most stars, excluding hypergiants and some supergiants. The parallax is given by $\displaystyle \theta_{p} = \frac{d_e}{d}$ where $d_e$ is the Earth-Sun distance and is $d$ the distance of the star. Instead, the angular size of an object with radius $r$ is ...

3

There isn't really a database as you request. Finding the ages of stars is difficult. Only one star has an accurately known age - the Sun. That comes from radioisotope dating of meteorites. For other stars we must rely on models to a greater or lesser extent and we can only estimate an age if the star has a mass or is in a phase of its evolution where things ...

2

In terms of asking the question in the title, there are various catalogues which include stellar ages, if you search on VizieR for the category "Ages" (in the "Astronomy" menu on the right-hand side) you will find a large number of such catalogues, but you will have to bear in mind that they focus on certain sets of objects rather than stars in general. One ...

1

According to wikipedia it is 10 degrees. Wikipedia cites Peißker et al, which uses the formula: $$\Delta\phi = \frac{6\pi G}{c^2}\frac{M}{a(1-e^2)}$$ to derive a relativistic periapse shift of 9.9 degrees per orbit.

1

Use Wien's displacement law - as you suggest. Let's assume that the spectrum you have been given incorporates almost all the flux from the star. This might be ok, so long as the flux is heading towards small numbers at each end of the spectrum? If so, then you can use the temperature-independent shape of a blackbody function to argue that some fixed fraction ...

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