The following figure is the HR diagram for the 481,000 nearest stars. As measured by spacecraft Gaia. I find the bunch of stars directly under the centre of the main sequence unexpected (these are yellow stars, so not white dwarfs or red dwarfs). I also find the bunch of stars to the right and slightly above the red giants unexpected. What are we looking at in both cases?

Article

http://www.cosmos.esa.int/web/gaia/news_20150807

Larger copy of image on http://www.cosmos.esa.int/documents/29201/652054/20150807bb.png/b0f21c56-2af5-4883-981b-963ec2422aab?t=1438827414281

What does “H R” mean?

bob(from black rock) said:

What does “H R” mean?

Hertzsprung–Russell. A H R diagram is a scatter plot of the brightness and temperature of stars. No distance information is recorded. See the Wikipedia article for more information, including interpretation notes.

I find the bunch of stars directly under the centre of the main sequence unexpected (these are yellow stars, so not white dwarfs or red dwarfs).

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Not sure where you mean. Can you give me an ordered pair?

dv said:

I find the bunch of stars directly under the centre of the main sequence unexpected (these are yellow stars, so not white dwarfs or red dwarfs).
Not sure where you mean. Can you give me an ordered pair?

(0.3, 7) I think these are what’s known as subdwarfs, also known as low-metallicity stars, Halo stars and Population II stars. Because they’re very old, they’re not found further towards the blue end of the spectrum (eg. not at 0, 4.5) because hotter more massive stars from Population II would have already decayed into red giants and white dwarfs.

The white dwarfs on this diagram are few and far between, at (-0.2, 4.5).

The “red clump” stars would be those in the high intensity region of (0.65, 0.7).

The “bunch of stars to the right and slightly above the red giants” (0.8, 0.5) could be asymptotic giant branch, also known as Mira variables and long-period variables.

While on the topic of the Gaia spacecraft, here’s a plot of 50,000 asteroids it’s observed.

http://www.cosmos.esa.int/web/gaia/iow_20150731

Click here for Full scale image

Very interest

btm said:

bob(from black rock) said:

What does “H R” mean?

Hertzsprung–Russell. A H R diagram is a scatter plot of the brightness and temperature of stars. No distance information is recorded. See the Wikipedia article for more information, including interpretation notes.

Here’s an H-R diagram created by mollwollfumble a year or two ago. Unpublished. It is unique in that it shows all the nearest stars, brown dwarfs AND planets. Note that brown dwarfs and planets all lie exactly on the same line as the main sequence.

Interesting