# Questions tagged [hr-diagram]

Use this tag for questions regarding the Hertzsprung-Russell diagram.

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### Why can I not get pymultinest running and what's the best way to generate CMD with coding?

I recently downloaded the isochrones environment for Python, and I installed pymultinest for sure, but when I import it in Jupyter Notebook it always says 'ERROR:root:Internal Python error in the ...
2k views

### When exactly does a sub giant become a red giant?

A simple, but interesting question I think. I understand that after the hydrogen exhaustion on the main sequence the post main sequence starts with the SGB where they burn hydrogen in a shell around ...
8k views

### Position of Neutron stars in H R diagram

Why is that Neutron Stars are never depicted in an H R diagram? They can be placed in the bottom right corner but you will never find any diagram in literature showing neutron stars.
5k views

### Why does the Hertzsprung–Russell diagram's x-axis go from large temperatures to lower?

In my textbook, the H–R diagram’s y-axis is $\log(L/L_{\odot})$ and values are higher as we go higher on the scale, but the x-axis is $\log(T_\text{eff})$ and gets smaller as we proceed to the right. ...
182 views

### Is there a stellar database that indicates how long ago stars in our Galaxy formed?

There are several ways of determining the age of a star: its position in the HR diagram, the presence of a protoplanetary disk, it belonging to a cluster... When did the stars in our Galaxy form? Do ...
51 views

### What would the HR diagram look like if the axes were scaled linearly instead of logarithmically?

The Hertzsprung-Russell diagram typically has its axes scaled logarithmically, and with good reason. The hottest stars are about 20 times as hot as the coldest ones (at least at the surface), and the ...
111 views

### Which star has the faintest absolute magnitude (largest magnitude) yet is still visible with the naked eye from Earth (either hemisphere)?

I am thinking about the Bright Star Catalogue and how it is not a good representation of a typical population of stars. The Bright Star Catalogue includes all the visible stars from Earth when viewing ...
46 views

### Why do blue horizontal branch stars turn downwards on the HR diagram as opposed to red horizontal branch stars which remain fairly constant?

Horizontal branch stars (HB) burn helium at their cores. Red horizontal branch (RHB) stars experience an increase in temperature while their radii decrease so their luminosity remains somewhat ...
503 views

### How can you determine the distance of a star using the magnitude equation?

In high school we are undergoing a short course about astronomy. It is stated that you can use the apparent and absolute magnitude (m, M) to get a distance (D) of a star, with the formula m - M = 5 \...
404 views

### Description of Henyey tracks on wikipedia incorrect?

So, if you search for Henyey tracks on wikipedia (I know, the shame of it!) you will come across this statement: The Henyey track is characterized by a slow collapse in near hydrostatic ...
2k views

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### Creating an HR diagram from tabulated stellar data

I teach statistics and study Astronomy. I'd like to create an activity for my statistics students using star data. They could enter the data into Excel and create an HR diagram. We are currently ...
117 views

### How does the stellar evolution for low and intermediate mass stars differ?

I'm trying to understand stellar evolutionary tracks for different masses. So far I have the general understanding from a cloud of gas and dust to a white dwarf, neutron star or black hole. What I don'...
58 views

### Graphing the evolution of stars on an HR diagram with timesteps

I have found countless images regarding the evolution of stars, plotted on an HR Diagram, like so (found on Wikipedia): Although this displays the time in each stage, it does not include any points ...
55 views

### HR diagram x-axis (color) and redshift?

I've read several articles and watched some videos on the HR diagram, but no-one seems to mention the effect of redshift on the color of a star. Is there some calibration step that needs to be applied ...
83 views

### "Early" and "late" nomenclature regarding O, B & K, M stars

The Wikipedia article Stellar Classification has a subsection "Early" and "late" nomenclature. It says: Stars are often referred to as early or late types. "Early" is a ...
259 views

### The life course for a massive star from birth to death using the HR Diagram

Could you explain to me the life course for a massive star (30-40 solar masses) from birth to death using the HR Diagram (by showing key events in its life)?
976 views

### Is there a flaw with the newer purposes and correlations attributed to the HR diagram? (And would a third axis of mass correct the enclosed flaw?)

When I was younger, I was looking at HR diagrams, and began to experiment with the HR diagram. I was looking at plotting different groups of stars on the HR diagram when I found RV Tauri stars. ...
627 views

### Why is the track of the subgiant stage almost horizontal on the HR diagram?

It is stated that: After the main sequence, as fusion weakens or stops in the core, outward radiation weakens. The helium core contracts and heats up. Gravitational energy is converted to thermal ...
157 views

### Position of a star on the HR diagram

Does the position of a star on a HR diagram depend on the magnitude system/color index used? I made a CMD of a particular cluster using HST WFC3/UVIS data, and when I plotted $F275W vs F275W - F606W$...