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 ...
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3answers
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 ...
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1answer
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.
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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. ...
6
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3answers
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 ...
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1answer
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 ...
5
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1answer
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 ...
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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 ...
3
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1answer
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 \...
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1answer
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 ...
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1answer
2k views

Redshift to calculate age of stars

In multiple articles I have seen the age of a star, within the milky way, referred to as its redshift (typically denoted by $z$). I know that $z$ can be calculated as $z=\frac{\lambda_{obsv} - \...
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2answers
69 views

Corresponding BV Value to a Hertzsprung–Russell

I have an example BV value from an astronomical catalog of 1.04 (33 Psc, HD Catalog 28). Given only the number 1.04, can that be charted on the HR, or do I need the individual components of the value ...
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2answers
461 views

Why do post main sequence stars enter the red giants branch?

I am an early graduate student in astronomy and have hard time understanding why do post-MS stars move up the RGB. Here is what I understand about post main sequence evolution of stars. As their ...
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0answers
48 views

What is the wiggle in the AGB branch?

In many HR diagrams, the asymptotic giant branch includes a wiggle. I thought that these are thermal pulses, but now I realise there are many thermal pulses, and I find only one wiggle. The wiggle ...
5
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1answer
72 views

Is a branch on HR diagram a line formed by stars in the same evolutionary phase, or the evolutionary track of an individual star?

Here is a HR diagram from Wikipedia, in the well-known form: Here is another one from the Stellar evolution article: I know that when stars leave the main sequence, they go to the giant branch ...
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2answers
115 views

How can red supergiants be cooler than dwarfs of the same spectral type?

The Stellar Classification Wikipedia article has a sentence: Red supergiants are cooler and redder than dwarfs of the same spectral type Which seems to be true, my course has a similar statement. ...
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86 views

Is there a galactic main sequence?

Stars can be plotted on an HR diagram, on which a main sequence is apparent, and stellar evolution can be plotted on on such a diagram as a function of mass. Is there an analog for galactic evolution? ...
4
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1answer
579 views

Variables in the Instability Strip

I was thinking about the possibility of determining what phase of evolution a variable star is in when it is located in the instability strip (say, a Cepheid object). Can you differentiate whether it ...
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2answers
187 views

Why does the Gaia color-magnitude diagram have this shape?

I was looking at the visualization tools of Gaia, and tried plotting a color-magnitude diagram. On the right hand side of the image, photGMeanMag (mag) (the amount ...
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1answer
127 views

Locating a star cluster on a Hertzsprung-Russell diagram with other color index

Recently I took pictures of the NGC 884 cluster in the B and I bands and selected some 30-what stars from them. I've reduced the data to a colour-magnitude diagram (absolute magnitude in the I band $...
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1answer
320 views

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 ...
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1answer
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'...
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1answer
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 ...
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1answer
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 ...
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1answer
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 ...
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1answer
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)?
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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. ...
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2answers
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 ...
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2answers
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 $F275W vs F275W - F606W$...
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1answer
526 views

Estimating a star's radius, temperature, and luminosity based on its mass

(See updated figure and description below.) I've been trying to generate ballpark estimates for the radius, temperature and luminosity of stars in the main sequence based solely on their masses (...
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1answer
245 views

Is there a formula to calculate any star mass from Luminosity, Radius, and/or Temperature (K)? [duplicate]

I know there is the Mass-Luminosity relationship, but I am wondering if there is a more accurate formula I can use based on the data points I have generated: Absolute Magnitude (based on class and ...