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21 votes
Accepted

What is going on with this (sub?) brown dwarf WISEPA J174124.26+255319.5?

I had a look at the original source of the measurements quoted on the Wikipedia page (Zhang et al. 2021) and the problem is simply systematic errors in the models that are being used to infer the ...
ProfRob's user avatar
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11 votes
Accepted

Are spectral subtypes a logarithmic scale, or a linear one?

Strictly speaking, neither. The types and sub-types are qualitatively defined in terms of spectral features (the presence or absence of various lines) and the relationship to photosphere temperature ...
James K's user avatar
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11 votes

Why are type 1b and type 1c supernovae called type 1 rather than type 2; if they result from large exploding stars, rather than accreting dwarfs?

It is fundamentally a question of spectral lines. Type I supernovae have no hydrogen lines, and type II have strong hydrogen lines. Type 1b have strong helium lines and no hydrogen lines, and type 1c ...
Justin T's user avatar
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7 votes
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How do we know that 2MASS J0523-1403 is a red dwarf?

The brown dwarf "limit" is about $0.072 M_{\odot}$ at solar metallicity (e.g. Chabrier et al. 2000) and is composition dependent. It gets a little higher in metal-poor gas and a little lower ...
ProfRob's user avatar
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4 votes

Approximate spectral type and luminosity given apparent magnitude and distance

You can calculate the absolute magnitude of a star: $$M=m-5\log_{10}(\frac{d}{10\,\text{pc}})$$ where $M$ is absolute magnitude, $m$ is apparent magnitude and $d$ is the distance. Then you take a look ...
User123's user avatar
  • 2,879
4 votes

Stellar classification spectral lines: chemical abundance vs temperature

Both explanations are right. The strength of an absorption line does depend on the abundance of a chemical element in the photosphere. But it also does depend on the temperature of the photosphere. ...
ProfRob's user avatar
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3 votes

What is a dM1e red dwarf star? What do the '1' and 'e', specifically, stand for?

The 9 main spectral types (the classical OBAFGKM ones plus the more recent L and T ones for brown dwarfs) indicate the general features seen in the spectra and are in descending of temperature (O is ...
astrosnapper's user avatar
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3 votes
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Any stellar entity named A1?

The Lowell observatory gives temporary designations in the form "A-number" to objects that it studies. A1 would be a temporary designation that the Lowell observatory could give an object. ...
James K's user avatar
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2 votes
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Can red dwarf stars have a spectral type of L?

Yes. Stars (those objects that are supported by hydrogen fusion) can be as cool as spectral type L2. Brown dwarfs can be as warm as M4/5 when they are young. i.e. there isn't a clear spectral type Vs ...
ProfRob's user avatar
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2 votes

Grammar of stellar classification

Normally, you would write G2V (with no spaces), as separating each part of the classification would cause some ambiguity. Basically, any star's classification would be written as 'Temperature class'+'...
WarpPrime's user avatar
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2 votes
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Eta Cassiopeiae star type; G0V? F9V? Both?

$\eta$ Cassiopeiae A has an estimated mass of 0.972 M$_\odot$, an estimated temperature of 5973 K, and a B-V color index of ~0.58[1]. In addition to the spectrum of the star, we look at these and ...
Joseph Farah's user avatar
2 votes
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Dataset for machine learning MK stellar classification

That I know there is the XHIP catalog via VizieR and you can enter a range in UMag (or B- and V-band) for example of -20 .. 20. Check the box SpType and Tc to get ...
Michele Bianco's user avatar
2 votes
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Is there a way to convert a list of stellar fluxes to a star type?

There is no direct conversion from a flux to a spectral type, but the ratio of fluxes, or the equivalently, the difference in magnitudes in different bands (e.g. $B-V$, $J-K$ etc.), known as a colour ...
ProfRob's user avatar
  • 155k
2 votes

Any stellar entity named A1?

A quick check with the Simbad database shows nothing with the identifier "A1". A search on the NASA Extragalactic Database turns up the galaxy cluster Abell 1 (or "Abell 0001", as ...
Peter Erwin's user avatar
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2 votes
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Is there a formula to calculate any star mass from Luminosity, Radius, and/or Temperature (K)?

I think the issue you are going to have here is that the position of a star in the HR diagram - which amounts to saying what the (2 dimensional) spectral type is - does not just depend on its mass. ...
ProfRob's user avatar
  • 155k
2 votes

How can I estimate how long will a main sequence star stay on the main sequence given its temperature?

The website on Main sequence stars fromr the Austalian national telescope facility lists star mass, temperature and life span: Mass/MSun Luminosity/LSun T=Effective Temperature/K Radius/RSun t=Main ...
James K's user avatar
  • 124k
1 vote

Have all Wolf-Rayet stars evolved off the main-sequence?

Wolf-Rayet stars have long been a subject of controversy in astronomy. Observationally, they are the class of stars that astronomers identify as being very luminous, having very little hydrogen, and ...
Daddy Kropotkin's user avatar
1 vote

Eta Cassiopeiae star type; G0V? F9V? Both?

The spectral type of a star is determined by looking at its spectrum. Sometimes authors will use other, approximate, relationships between spectral type and colour or mass, or they will look at the ...
ProfRob's user avatar
  • 155k
1 vote

Does "spectral type" and "stellar classification" refer to the same thing?

"Spectral Class" System of classification, including O, B, A, F, G, K, M. Stellar classification includes the Harvard system, and also other methods of classification including the Yerkes ...
Astrovis's user avatar
  • 733

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