Are nearby stars generally high or low luminosity stars?

Question

Im in an astronomy class and i'm TOTALLY LOST. I cant find the answers to any of my questions online. Anyone here really good at astronomy??? I have to pass this class to graduate!! :-(

Are nearby stars generally high or low luminosity stars?

Answer 1

The majority of the closest stars to us are low luminosity. Of the couple dozen stars within 12 light years of us, there are only 3 which are brighter than the sun. This would imply that the great majority of stars throughout the galaxy are faint little dwarfs.

BTW, those 3 stars are Sirius, Procyon, and Alpha Centauri.

And here's another perspective I came up with on my own from studying tables of hundreds of stars. Of all the stars we can see in the sky with the naked eye, there are only two which AREN'T brighter than the sun. Here, it seems that I'm saying just the opposite, but the reason for that is that we are seeing only the brightest stars and all the ones less bright than the sun can't be seen at all over about 30 light years.

Note: I would be more than happy if someone can find a third star, but I haven't been able to. The two stars I found are Tau Ceti and Epsilon Eridani.

Answer 2

luminosity has nothing to do with how nearby they are. Luminosity is an intrinsic property of the star. What you probably mean, is the apparent magnitude, the further a star, the less bright it is, it's also a logarithmic scale. if you have a high luminosity star and a star with low luminosity, and the bright star or high luminosity is farther away than the low luminosity star, it is possible that they have the same apparent magnitude.

Answer 3

Most nearby stars are very low luminosity. That is because most stars in the universe are low luminosity, so the most of the stars in any one place are low luminosity. There are a few "medium" luminosity stars nearby, like Sirius and Alpha Centauri, but all the really luminous stars are far from our solar system.

Answer 4

Most of the stars just about anywhere are low-luminosity stars. You just can't see them easily past 30 lightyears or so. A chart I've seen makes it appear that the distribution of star density versus absolute magnitude is roughly Gaussian and has a peak at Mv=+11.5, with a standard deviation somewhere around two magnitudes. A +11.5 absolute magnitude star has a luminosity of 0.002 sols (7.6E+23 Watts) and a mass of about 0.13 suns (2.6E+29 kg).

The stellar luminosity function is not well-known at the lowest magnitudes, and it's possible that, although the star density for the brighter stars declines as a normal distribution would, the low side of the distribution might not decline so fast. It might not decline at all... gravitational accretion might have made brown dwarves floating around below the detectability of our IR sensors very common.

For stars of absolute magnitude +5 or brighter (i.e. for stars brighter than the sun), you can estimate the density of stars as follows:

phi = -0.03138601 Mv^2 + 0.4732912 Mv - 0.09821123
rho = 10^phi

The rho is the number of stars within a half-magnitude of your chosen magnitude Mv per 10000 cubic parsecs.

For example if Mv = +2.0, then...
phi = 0.7228, rho = 5.28
In other words, there should be, on the average, about 5.28 stars per 10000 cubic parsecs having absolute magnitudes between +1.5 and +2.5, in parts of the galaxy similar to the part where the sun is now.

For stars having absolute magnitudes between +5.0 and +8.0, do this

rho = (4 Mv + 67) / 3

For example, if you put in Mv=+6.0, you get rho=30.3333, and that's how many stars might be found in 10000 cubic parsecs between the absolute magnitudes +5.5 and +6.5.

For stars having magnitudes between +8.0 and +10.0, do this:

phi = +0.05859771 Mv^2 - 0.8914642 Mv + 4.9
rho = 10^phi

When Mv = +9.0,
phi = 1.6232
rho = 42.0

So you might expect to find 42 stars per 10000 parsecs between magnitudes +8.5 and +9.5.

I don't really feel secure about curvefitting the model to estimate star densities for stars dimmer than absolute magnitude +10.

Answer 5

Generally, the stars in the nearby neighborhood are fairly low luminosity stars, the exception probably being Sirius - 8.6 light years away. Most are dwarves (like our sun), and very common.

Answer 6

they are low luminosity,, Most stars we see are a low luminosity, the high luminosity stars are the bigger class stars and so forth up to supergiants

Answer 7

It depends on your definition of "NEARBY" --------- say 20 light years maybe?

Here is a list of the 26 BRIGHTEST stars in the sky--- with magnitude and distance away.
http://www.astro.wisc.edu/~dolan/constellations/extra/brightest.html

Answer 8

Some answers here:
http://www.astro.wisc.edu/~dolan/constellations/extra/nearest.html
Check out the last line on the page most stars near by are less luminous.
Hope this helps

Answer 9

they would be low temperature stars ,, this is because most stars in the universe are low temp. stars, to the exeption of blue stars which are very high temp. surface

Answer 10

Have you looked in the accompanying textbook to this particular course?
I'd be willing to bet you'd find the correct answer there!