Talk:B-type main-sequence star

I have to address the 'The spectral luminosity class is typically V' again. Thank you for bringing forward examples like V372 Carinae and discussing it, @Lithopsian, @21.Andromedae. However, the statement is still incosistent with the definition of luminosity class, which was my original worry. You can compare to the Main sequence article that e.g. has a line 'These main-sequence stars, or sometimes interchangeably dwarf stars, are the most numerous true stars in the universe and include the Sun.' In case other Wikipedia pages are not a source you want to see, I looked it up in the IAU Office of Astrononomy for Education (OAE) page at astro4edu.org: 'Roman numerals are used to denote luminosity class: Stars on the main sequence burning hydrogen are classified as dwarfs (V)' [1], ' "Dwarf star" is a synonym for a star on the so-called main sequence' [2]. (The terms and their definitions on the pages have been approved by a research astronomer and a teacher.)

In case none of you disagrees I will delete the 'typically' from the corresponding pages. Stevinger (talk) 05:48, 18 January 2026 (UTC)

There is a good difference between theory and practice. While it would naturally be expected that a luminosity class reflects the actual evolutionary stage, this is not always the case, like 55 Cancri, Gliese 777, Gamma Cephei, Mu Ceti, Delta Capricorni, Merak, Rasalhague, 23 Ursae Majoris, Menkalinan and Kepler-410 and many more that are main sequence stars in evolutionary terms, but were assigned IV or V-IV luminosity classes based on the spectrum. 21 Andromedae (talk) 12:57, 18 January 2026 (UTC)

The reply above by 21.Andromedae included Kappa Andromedae, but was deleted because it 'now has a main sequence luminosity class' (you can also write ~~Kappa Andromedae~~ btw, makes it much easier to reply to a post that was changed late in time). Stevinger (talk) 10:08, 21 January 2026 (UTC)

I decided to look at two objects of your list, Rasalhague, since I haven't heard this name before and Kappa Andromedae, since I know this obect.

Alpha Ophiuchi: Rasalague has three different luminosity classes that were measured for it. Basically anything from A3V to A4III to A5IVnn. Naturally two of the three (V, IV, III) do not reflect the actual evoluationary stage it is in, no matter what this stage is.

Kappa Andromedae: As you already saw, the spectral type and luminosity class just needed an update and there is no difference left.

The amount of objects you present indeed proves several things. E.g. that there are lots of borderline objects between the luminosity classes and that it is difficult to measure for some objects the luminosity class and/or the evolutionary stage in practice. But it does not prove 'The spectral luminosity class is typically V' for main-sequence stars. Stevinger (talk) 01:35, 22 January 2026 (UTC)

And to add to the already extensive list of examples: Nu Indi, GJ 2030, Chi Leonis, and 171 G. Puppis. 21 Andromedae (talk) 22:55, 20 January 2026 (UTC)

Thank you also for these objects. My fault was to say I would accept the 'typically' if 'you can name a main-sequence star example with a different luminosity class', not specifying that I of course meant an object that is a main-sequence star and being assigned a different luminosity class in the very same publication or directly stating so. I did not expect that you present me with an extensive list of examples, in which, if I checked it correctly, none of the objects has a deviating main-sequence nature / newly assigned luminosity class from the same publication. If different publications give the deviating values and do not discuss it this can have lots and lots of different reasons. Please compare that Rasalhague could be anything from dwarf, to subgiant, to giant based on the measured luminosity classes from different publications. Stevinger (talk) 01:47, 22 January 2026 (UTC)

R136a1 and many similar massive stars, most (effectively all, but not all classified in Wikipedia as main sequence with references) cool subdwarfs (eg. GJ 1062 and Mu Cassiopeiae - possibly not a clean example but definitely a main sequence star considered to be a subdwarf). Am I too cynical to think that half of these are going to get edited in the next day or two?

More seriously, are you here to push an agenda or to improve the wiki? At the risk of opening a huge POV can of worms, luminosity class might benefit from some discussion of the matches and mismatches with evolutionary stages of the same or similar name. Reliable references needed of course, which might be hard to find for some cases: the rotationally-mised massive stars and cool subdwarfs should be simple enough, perhaps also some for giants and supergiants which bear almost no relation between the luminosity class and the underlying physical state of the star. Perhaps simple explanations of the basis for derivation of spectral luminosity classes and the definition of the related evolutionary state might be sufficient for the subtler cases that we're arguing about here. There's a little bit there now, but it is all sort of vague. Lithopsian (talk) 16:15, 21 January 2026 (UTC)

I could ask you the same thing regarding the agenda, especially after your sentence what the luminosity class might benefit from. Yes, I am here to improve the wiki and in this case by deleting the 'typically' from the incorrect sentence 'The spectral luminosity class is typically V'. I did so before, it was reverted and I got no satisfying answer yet why it was done. Stevinger (talk) 02:35, 22 January 2026 (UTC)

Don't get me wrong: I fully agree that anything can be added to luminosity class, if an existing reliable reference can be found, as you emphasized. Stevinger (talk) 04:36, 22 January 2026 (UTC)

btw ~~GJ 1062~~. I am not sure if I missed something. But the reference you gave for the main-sequence nature of GJ 1062, presents LHS 20, as they call it, as a subdwarf. Please correct it, if I missed what you meant, I found the object is only mentioned once in Table 1 (as a subdwarf). Stevinger (talk) 02:37, 22 January 2026 (UTC)

I suggest taking that as disagreement and moving on to something more constructive. Lithopsian (talk) 15:56, 18 January 2026 (UTC)

I was hoping, too, that this would be a fast clarification.

I also looked at V372 Carinae. Thank you for the clarification with the Jin publication. A spectral type of B2V was spectroscopically found and used also as recently as 2024, making it potentially a nice example of a main-sequence star.

Thank you also for your examples. These examples would prove a sentence like 'The measured spectral luminosity class is typically V', if that is what I assume you mean. But 'The spectral luminosity class is typically V' is against the definition of main-sequence stars. Either they belong to the main-sequence lists, then they are luminosity class V or they don't, then they are not meant (to be) in the main-sequence list. Please compare a comparable sentence like 'Typically brown dwarfs are not on the main-sequence'. This sentence is incorrect, too, since either objects have enough mass to fuse hydrogen or they don't. This does not mean, that it is excluded that some authors determine the same border line objects as brown dwarfs and others as main-sequence objects in different publications.

The conclusion that examples, where different publications give luminosity classes and a main-sequence nature of an object, prove a mismatch of its evolutionary stage is not from the references given and thus not cited. I remembered that you wrote 'Uncited material may be removed at any time' to someone in the 'A-type main-sequence star: Revision history'. So I followed that link and found there: 'All content must be verifiable. ... and it is satisfied by providing one inline citation to a reliable source that directly supports the contribution.'

The examples given so far do not directly support the contribution 'The spectral luminosity class is typically V' and I gave references that IAU Office of Astrononomy for Education (OAE) material is inconsistent with this statement. I suggest one of you (@21.Andromedae, @Lithopsian) provides such a direct support of the contribution, if you want to, or it should be changed/deleted. Stevinger (talk) 04:27, 22 January 2026 (UTC)

At this point, i and Lithopsian have demonstrated that a luminosity class does not strictly correspond to the actual evolutionary stage using the simplest, but more straightforward, proof: examples deviating from this class, and even an entire luminosity class (subdwarfs) that is not 'V'. You even said after Lithopsian's post regarding uncited material removal that you would happily except the 'typically' if Lithopsian can name a main-sequence star example with a different luminosity class but with examples and more examples shown, you now says that the clarification was not fast, and the only remaining arguments (which i will answer below) against the fact that the luminosity class is typically 'V' are the following:

These examples would prove a sentence like "The measured spectral luminosity class is typically V", but this has the same meaning as "the luminosity class is typically 'V'", and is wrong because luminosity classes aren't necessarily "measured" but sometimes estimated by eye.
A supposed disagreement with the definition of main sequence stars, the weakest and most bizarre argument. A main sequence star isn't defined as one with a luminosity class 'V', but as one fusing hydrogen at the core at large scales, as indicated by the aforementioned Wikipedia article: Stars spend the majority of their lives on the main sequence, during which core hydrogen burning is dominant. These main-sequence stars, or sometimes interchangeably dwarf stars [...] and the aforementioned IAU OAE ref. The IAU Office of Astrononomy for Education stating that Stars on the main sequence burning hydrogen are classified as dwarfs (V) is just speaking of what happens in theory (and in a very gross and somewhat misleading way, as this is not exactly how luminosity classes work, but since their website is "dedicated to supporting astronomy Education at primary and secondary school level", this simplistic definition is enough), not in practice, if you want a reference talking about such classifications in practice, see this or some refs listed in the next topic.
A likely problem of referencing with the word 'typically', based on the sourcing policy and Lithopsian's advice, which is the best argument, at least at first look, but with a further look, this is fundamentally flawed. No reference for the word is needed, because this is implicit in the very definition of luminosity class: a classification based on the surface gravity (which theoretically correlates with luminosity), not on the actual evolutionary stage of the star (this paper says that The authors of the MK system have always emphasized that the luminosity class is a description of the spectrum (for instance Morgan, 1984).) The word 'typically' merely reflects the subtle differences between both concepts (lum. class and evolutionary stage). On the other hand, saying that 'the luminosity class is V' would require a citation, because it is implying that both concepts amount to the same thing and guarantee that one will be always equivalent to the other. In other words, a luminosity class 'V' simply says that the surface gravity indicates a luminosity similar to that of main sequence stars, not that the star is in the main sequence stage of evolution.

And, to satisfy your requeriment, there are references saying that luminosity class ≠ evolutionary stage. The most direct ref is the first mentioned, which states that the vast majority (emphasis) of dwarf stars (MK luminosity class V) are in the main sequence phase (burning hydrogen in their cores) and viceversa, but some exceptions exist in both directions.

For an analysis of B and O-type stars, there is this, which concludes that A luminosity class V does not correspond to the entire main sequence above 20 M_☉. Dwarf stars are observed all the way from the ZAMS to the TAMS only for the 15 M_☉ track. As mass increases, an increasingly larger portion of the main sequence is spent in the luminosity class III, and dwarfs are not seen on the main sequence above 80 M_☉. Supergiants (luminosity class I) appear before the end of core-hydrogen burning above 50 M_☉. Consequently, the distribution of luminosity class V stars does not trace the main sequence and cannot be used to constrain the size of the convective core and is complemented by the the first ref that also states that For O stars, one should not equate the main sequence (MS) phase of stellar evolution with luminosity class V. O-type giants and even supergiants are still burning hydrogen in their cores (Martins and Palacios, 2017).

For the A spectral type, we have this ref stating that fast rotation in A-type main-sequence stars can induce luminosity effects and make they appear brighter and more evolved than what they actually are, this ref stating the same for metal-enriched stars (just for note, the same occur in the opposite direction for metal-poor stars (e.g. cool subdwarfs)), and this site from Eric Mamajek saying that among late As, the spectral differences between dwarfs and subgiants are subtle and may not necessarily signify differences in luminosity. For further reading, see this.

For the F spectral type, there is this paper (which comprises B0 to F5 stars) and states that Of note, ∼770 of the stars plotted are subgiants according to their XHIP luminosity classes, while only ∼250 stars have log g < 3.8, suggesting some spectral types are in error. and this, which comprises A to K spectral types and concludes says that the luminosity classes IV and V do not differentiate the evolutionary state of the stars very well, as pointed out in Section 2.4. A similar paper even points out stars "roughly on the main sequence" have "luminosity class V or IV".

For the G and K spectral types, there is this ref showing in their Figure 1 stars classified as subgiants in the main sequence branch of their HR diagram, and vice-versa, this site stating that it is clear that many spectral type IV objects in literature among early Ks are misclassified dwarfs, which are much more numerous.

And for the M spectral type, there is this, classifying M subdwarfs as main sequence stars.

For last, a main sequence star with a spectral type with no luminosity class (e.g. A4, K6, M0) would not be a main sequence star based on the absence of a luminosity class 'V' (which appears to be your understaining about main sequence classification)? The same for a star never assigned a spectral type, but clearly in the main sequence branch? S Carinae for example has no luminosity class, but is still a giant star. 71 Cancri is a main sequence star, but without a luminosity class. Just for note, the luminosity class can also be affected at some extent by some intrinsic processes (page 10 in Gray, Napier, and Winkler (2001)). It will also depend on the calibration used. Most spectral types were derived in the last century, when the calibrations of main sequence (and other classes) were not totally understood.

21 Andromedae (talk) 00:16, 4 February 2026 (UTC)

Not sure where to start. There are so many misunderstandings. But I might have understood now, what the difference to your point of view is. But let me clarify a few things first, in opposite order to yours:

No to your last paragraph. An object without determined luminosity class can be on the main-sequence or it is not. However, for S Carinae you could use the spectral type MIII (2010A&A...514A...2I) or M4III (2010PASP..122.1437P) or M2-3IIIe (1964BS....C......0H (ADS)) or M2.5 IIIe (2007AN....328..889K).

You write M subdwarfs are classified as main-sequence stars in this. This isn't incorrect, but it says that if there are only Population II stars than the main-sequence would be the subdwarf sequence, but it also says that there are about 600 times more Population I stars, why the main-sequence was defined as it is.

Then there is a lot about how objects are misclassified and how differences are subtle, this is all fine, but as you say you are trying to 'demonstrated that a luminosity class does not strictly correspond to the actual evolutionary stage', which is not relevant for the luminosity class representation of objects on the main-sequence (please see below).

I am a bit suprised how you discredit the aforementioned IAU OAE ref and the IAU Office of Astrononomy for Education. Yes, this is for astronomy education, but IAU asked for it to be written and you might have missed that 'Term and definition status: This term and its definition have been approved by a research astronomer and a teacher.' If you disagree: 'If you notice a factual error in this glossary definition then please get in touch.', then a person from IAU can possibly explain it better than I can. Instead you suggest to see this, which might be a good reference. However, I could in contrast to the IAU reference not determine whether it is peer reviewed (mostly because searching for it always points me to the Encyclopedia of Astronomy and Astrophysics, which is not the same).

To your point 1. I should have written estimated, but no matter if they are measured or guessed, 'The estimated luminosity class is typically V' and 'The luminosity class is typically V' is not the same thing. As I wrote before for Alpha Ophiuchi: With estimated spectral types of A3V to A4III to A5IVnn, the object is likely V, III or IV, so the estimated luminosity class is possibly typically V for the star, but the accurate luminosity class, once properly determined is always the same one (well, within a human lifetime and with these possibilities). Stevinger (talk) 04:07, 5 February 2026 (UTC)

So let me try again. If I understood the misunderstanding correctly, you will disagree right away and hopefully see, what I see differently and with me IAU and others:

The page or pages that are discussed deal with main-sequence stars. You should not start on the aforementioned Wikipedia article in line two and ignore line 1: 'In astrophysics, the main sequence is a classification of stars which appear on plots of stellar color versus brightness as a continuous and distinctive band.' A main-sequence star was defined because it lies on the main-sequence, this distinctive band described there. It was found that all objects lying on the main-sequence do fuse hydrogen in their core. This is why it says 'these main-sequence stars, or sometimes interchangeably dwarf stars'. Now you argue the other way around. Everything that is fusing hydrogen in its core is a main-sequence star. That these objects lie on the main-sequence is however incorrect, as already subdwarfs demonstrate, some are fusing and are not on the main-sequence (they are maybe fusing hydrogen, but they are not lying on the aforementioned distinctive band of stars forming the main-sequence).

If the page says main-sequence stars the reader can expect to find a discussion about objects lying on the main-sequence, which all have luminosity class V. If you name the page B stars, M stars and so on of course other objects should be involved.

You write 'examples deviating from this class, and even an entire luminosity class (subdwarfs) that is not 'V'.' Subdwarfs are not on the main-sequence, they are '1.5 to 2 magnitudes lower than that of main-sequence stars of the same spectral type.' (subdwarfs or here or here on page 34). Even when following your logic that stars fusing hydrogen in the core have the same evolutionary stage than main-sequence stars, the statement at the beginning of this paragraph is not true. As I wrote to Lithopsian on the GJ 1062 page, there are subdwarfs like for example SDSS J141624.08+134826.7 that are brown dwarfs, so it is simply impossible that all subdwarfs fuse hydrogen and some will never do so in their lifetime at the same time.

So again, please don't conclude from every object on the main-sequence fuses hydrogen directly to every object fusing hydrogen (in its core) is on the main-sequence. Actually your 'most direct ref is the first mentioned' clarifies that, too: 'For the sake of consistency, throughout this entry we will consider luminosity classes as spectroscopic or morphological categories. Therefore, we will avoid equating dwarfs or luminosity class V with the main sequence (as originally done), for which we will reserve its evolutionary or astrophysical meaning of being composed of stars burning 1H in their cores.' (page 6). This 'equating' as they call it is, however, historic but not only historic and still in use. Since two IAU references seem not enough, please consider this reference: Unsöld Baschek 'The New Cosmos: An Introduction to Astronomy and Astrophysics'. This book exists since 1969, has seen 7 editions so far and will get an 8th edition in 2030 if I found it correctly. It is a bit difficult to argue, since not all of it is publicly available. But I hope this link to the at least 5th edition works: New Cosmos (otherwise please search for 'luminosity class V' on the left, I could only find this partly german surrounding via google). It tells you: Main sequence (dwarfs) and this is how it is still defined. This 'equating' is btw also on wikipedia e.g. in the wording 'These main-sequence stars, or sometimes interchangeably dwarf stars' on the main-sequence page or in the table of luminosity class.

Of course any new opinion and idea can be brought forward and will be adapted by IAU if valid and well explained, but it doesn't seem to be the job of Wikipedia to establish alternative views on the main-sequence. I write it that way, because the only direct reference 'the first mentioned' was fully published in 2026. It might be adapted by IAU and the community or it might be rejected by most future authors, much to early to say. (It is a bit similar to alternative exoplanet definitions. The IAU working definition might be changed in the future, but for the moment it is usually what is used to classify exoplanets, in publications, not in the archives since they want to be complete in any case.) Stevinger (talk) 05:01, 5 February 2026 (UTC)

I sense no progress, although I realise my lack of participation in pointless arguments has already been taken as conceding the point. I have canvassed outside opinions in the hope of breaking the logjam. Not very "outside", just at Wikipedia talk:WikiProject Astronomical objects. There is always the option of WP:RFC or even stronger interventions, but fingers crossed editors with astronomical knowledge will be enough. Lithopsian (talk) 14:58, 4 February 2026 (UTC)

Nobody has to participate. But how long should I wait for a reason after something was inverted and your message 'I suggest taking that as disagreement and moving on to something more constructive.' Then deleting the two references I inserted and inverting again without putting in a reference yourself, based on a 'consensus' that wasn't reached is not the way to handle things. But thank you for asking for outside opinions. Indeed that might help. Stevinger (talk) 03:20, 5 February 2026 (UTC)

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