Expanding the HR diagram to include planets

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Expanding the HR diagram to include planets

Post by marasama on 8th December 2008, 12:01 am

Just thinking on how it would look.

So you got the alphabets.
ABCDEFGHIJKLMNOPQRSTUVWXYZ
Stars & brown dwarfs are:
W OBAFGKML TY wD
Carbon Stars
CNR S J
Problematic letters:
IQUVXZ

You are left with:
EHP
H = For giant planets, sort of like the Hydrogen Dwarfs
E = Earth-like, Terrestrial. Yeah, it says it is problematic, but it is not a galaxy.

Any thoughts?

Reference:
http://www-int.stsci.edu/~inr/ldwarf1.html

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Re: Expanding the HR diagram to include planets

Post by Sirius_Alpha on 8th December 2008, 12:49 pm

I don't think it makes much sense. The HR diagram uses temperature and brightness as its axes. For non-fusing objects, such as planets, it could get very hazy and one would find some gas planets and terrestrial planets in the same "spectral type" and what-not.

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Re: Expanding the HR diagram to include planets

Post by Lazarus on 8th December 2008, 3:50 pm

Well brown dwarfs don't do fusion either (except for a brief phase in their youth), but we still have spectral type T, and the proposed-but-not-yet-convincingly-observed spectral type Y.

I doubt planets which aren't gas giants would have similar "spectral types" - remember the spectral type is primarily a means for classifying the object's spectrum: it is NOT a temperature classification. (The fact it works as one is a happy accident of the fact that to a large extent, stars tend to be made of the same stuff)
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Re: Expanding the HR diagram to include planets

Post by Sirius_Alpha on 8th December 2008, 4:52 pm

CFBDS J005910.90-011401.3: reaching the T-Y Brown Dwarf transition? is the best case for a Y0V type star.

It is true, that the spectral types of stars are based off of their spectrum. My mistake. In this case, perhaps the Sudarsky classification scheme may provide a reasonable "spectral type" for a planet. As the different classes are expected to have different spectra. So perhaps a spectral classification could work for gas planets. For terrestrial planets though, I don't think it'll work.

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Re: Expanding the HR diagram to include planets

Post by marasama on 10th December 2008, 1:49 am

Sounds like "H" would be the next logical letter. Even if it falls for sub-brown dwarfs.

And there is still a hand full of astronomers that sort of consider Jupiter, not a planet.

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Re: Expanding the HR diagram to include planets

Post by Darkness nova on 22nd December 2008, 4:21 pm

P for plutiods......

As for this whole idea well.....I dunno.

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Re: Expanding the HR diagram to include planets

Post by Lazarus on 22nd December 2008, 5:07 pm

Hang on a minute, are we talking about extending the spectral type sequence or the Hertzsprung-Russell diagram?

from Wikipedia...
There are several forms of the Hertzsprung-Russell diagram, and the nomenclature is not very well defined. The original diagram displayed the spectral type of stars on the horizontal axis and the absolute magnitude on the vertical axis. The first quantity (i.e. spectral type) is difficult to determine unambiguously and is therefore often replaced by the B-V colour index of the stars. This type of diagram is called a Hertzsprung-Russell diagram, or colour-magnitude diagram, and it is often used by observers. However, colour-magnitude diagram is also used in some cases to describe a plot with the vertical axis depicting the apparent, rather than the absolute, magnitude. Another form of the diagram plots the effective temperature of the star on one axis and the luminosity of the star on the other. This is what theoreticians calculate using computer models that describe the evolution of stars. This type of diagram should probably be called temperature-luminosity diagram, but this term is hardly ever used, the term Hertzsprung-Russell diagram being preferred instead. Despite some confusion regarding the nomenclature, astrophysicists make a strict distinction between these types of diagrams.

The reason for this distinction is that the exact transformation from one to the other is not trivial, and depends on the stellar-atmosphere model being used and its parameters (like composition and pressure, apart from temperature and luminosity). Also, one needs to know the distance to the observed objects and the interstellar reddening. Empirical transformation between various colour indices and effective temperature are available in literature (Sekiguchi 2000, Casagrande 2006).
It is definitely possible to extend the luminosity and temperature axes, though once external heating becomes relevant it is questionable whether it is really useful to plot such objects on the diagram.
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Re: Expanding the HR diagram to include planets

Post by marasama on 23rd December 2008, 8:05 pm

Hmm. Sounds almost as if the classification for stars might need to be updated eventually.

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