Talk:Stellar classification

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[edit] Harvard vs MK Spectral Types

I would like to bring to note that previously it was stated that the Harvard and MK Spectral Types were synonymous. I would bring to note that this is not true. While they occupy the same points with regards to classification, the Harvard Spectral Type is directly related to the spectra of the star, while the MK spectral type is related moreso to the luminosity of the star. Since the article uses "spectral type" as a general term, it may be important to note that these two distinctions can be made.

TAAriona 08:24, 2 March 2007 (MST)

[edit] Mg != Manganese

The last item in the table of unusual spectral notations, indicates that "Mg" indicates unusually strong "Manganese" lines. Well, Mg == Magnesium. Mn == Manganese. I don't know which it's supposed to be, but it's clearly an error. The one reference given does not mention this notation. Myrrhlin 04:47, 27 October 2006 (UTC)

I've made the change of "Mg" to "Mn". "Mercury-manganese stars" (HgMn) are a fairly common class of chemically peculiar A stars. BSVulturis 17:37, 15 December 2006 (UTC)

[edit] WO?

There's a rare WO Wolf-Rayet kind of oxygen emission star. I'll be back l8R. Rursus 12:30, 23 October 2006 (UTC)

Done, thanks, CarpD 12/20/06

[edit] Colors

[edit] Green stars?

I have heard, that there are also green stars. How do they fit in this scheme?62.46.183.46

There are no green stars. In some cases a white star orbiting an orange star may look greenish, but it is only due to the contrast. --Jyril 13:13, Mar 8, 2005 (UTC)
That's a bold statement indeed! Especially because of the science philosophy requirement to search the entire Universe (Gosh!), to be proven true! I'm in search for green stars - have found no yet - but the Veteran Amateur Astronomer Patrick Moore claims, in the 1979 version of his The Guinness Book of Astronomy (no ISBN given, the Swedish translation has ISBN 91-37-07790-2, the stmt last in the chapter about the Constellations) that β Lib sometimes can be observed to be slightly green tinted. Now this is a little odd since β Lib is spectral type B8V ("blue white" main seq) - but it's also a star which spectrum sometimes exhibit nebulosity lines. Rursus 17:13, 4 January 2007 (UTC)
Stars with planetary nebulae can be green. But it's the nebulae, rather than the star itself. 66.30.119.55 00:10, 22 June 2006 (UTC)
If you want to just take the peak wavelength, you could argue that are green stars. However, the Sun's peak wavelength is green, and it doesn't appear green. In fact there is no black body spectrum that appears emperically green. (P.S. Stars emit in a black body spectrum) —Preceding unsigned comment added by 143.167.7.109 (talk) 12:28, 18 April 2008 (UTC)

[edit] Yellow sun?

How exactly can the sun be yellow when it gives us full-spectrum (white) light?

Short answer: the sun by itself is white white white. In the morning and the evening it's light is traveling thru thick layers of atmosphere, that spreads the light by the Rayleigh dispersion. When people say the sun is yellow, they don't know what they're talking about. Rursus 17:17, 4 January 2007 (UTC)
This isn't going to be a very scientific explanation, but here goes...
The colours of the sun and other stars are usually described as we see them on Earth, i.e. through the atmosphere. The atmosphere itself (and particles of dust etc within it) absorbs some of the light and scatters and reflects some of it, which means that the colour of the light which passes through it changes - the more yellow part of the light is not absorbed. This absorption is also why the sky is blue (the gases in the atmosphere themselves do not give it this colour). The effect can be seen when comparing the appearance of the sun and sky at midday to their appearance at sunset. At sunset, the sun appears on the horizon and its light passes a greater distance through the atmosphere to reach you. More light is absorbed over this greater distance, making the sun and sky appear redder. Try Sky and Diffuse sky radiation (needs work...). If anyone can improve on this explanation and/or can think of a better place to put it, please do.
SteveW 12:26, 8 Mar 2005 (UTC)
Well Sun shines in every color, but the intensity is peaked in green and neighboring light so it gives us an impression of yellow. It is explained here. Here's info about the colors of stars -- you see the blue/white/yellow/orange/red classification isn't that accurate. Too bad it hasn't carbon star colors. They are truly red. --Jyril 13:13, Mar 8, 2005 (UTC)
The Sun itself is white. It is only "yellow" in a technical, spectroscopic color sense. That is, "yellow relative to Vega". Vega is a nice spectroscopic reference, but being A class, it is visually quite blue. Only spectroscopists, and hypothetical natives of Vega, consider Vega white, and the Sun yellow. Unfortunately, many years of tables in textbooks (and now wikipedia) saying simply A/white,G/yellow, and neglecting to provide context, have created a great deal of misunderstanding. The Sun is yellow relative to A class stars, and cyan relative to M class stars. Also purple relative to green grass, and green relative to purple dinosaurs. Pale red relative to the noticably bluish D65 blue sky standard whitepoint, and pale blue relative to the noticably reddish D50 incandescent indoor whitepoint. It is right on the blackbody curve, in the region most see as untinted. In a word, it is white. 66.30.119.55 01:21, 22 June 2006 (UTC)
The table in the article should have two columns. One with the standard relative to Vega color (white, yellow, etc). Explained. And one with visual colors. Better visual colors. The current descriptions ("Light yellow", "White with bluish tinge", etc), seem rather bogus. 66.30.119.55 01:21, 22 June 2006 (UTC)
Actually, the current descriptions look like an attempt to tweak spectroscopic colors to be less implausible as visual ones. Recognizing that the two are distinct should make that easier :). 66.30.119.55 01:32, 22 June 2006 (UTC)

[edit] Asphyxiated space colors of stars

So what color would stars be if you were outside the atmosphere? Would they just all be white? Zhatt 23:37, 7 December 2005 (UTC)

The red and blue stars do look red and blue whether viewed below or above the atmosphere, because the other colors present are not at a level to alter the color. These stars are on the opposite ends of the surface temperature range for stars. The low temperature T-class brown dwarfs can look somewhat magenta due to only two colors present (blue and red) in the spectra. [Atmospheric molecules, allowed by low temperatures, create a more complex spectra.] [George1806, 12/22/05]
The sun will look white in space because all three color cones within the eye will be overwhelmed from the sun's enormus intensity. White is the result when the input flux to each of our three different color cones are equal. However, some distance after the sun becomes a point-source (<1 arcmin) rather than a disk, its true color would be observable to the unaided eye. [George]
Heliochromology (I made this field name up for this subject :)) is producing results indicating the sun is, indeed, white (possibly slightly bluish-white). This assumes one is above the atmosphere and is seeing the sun at a much reduced flux level (in the normal photopic range for our eyes). The spectral irradiance of the sun above our atmosphere (AM0) peaks in the blue-green (cyan) portion of the spectrum. [Actually, there are two peaks close together.] Our atmosphere causes extinctions in the spectra of direct sunglight such that its color is altered. A limited poll taken in the BAUT forum (www.bautforum.com) reveals about half see a mid-day (overhead) sun as yellow-white, and almost half see a white sun (others see yellow). [Numerous variables have attempted an explanation for this, but much seems subjective.] [George]
A SAD instrument (Solar Attenuation Device) was used to reduce the solar flux by 99.9%. It's sad because it costs about 20 cents to make. [old pencil glued to paper plate with small radial slot; then spun by an electric drill - a simple stobe.] A more elaborate device, SPACC (Stellar Post-Atmospheric Color Corrector), was developed to reconstitute the sun's true spectral irradiance by passing direct sunlight on Earth through a prism, then using a calibrated mask to reproduce the sun's original spectral irradiance. Combining this light into one spot allows the eye to see the true color of any light source. [Homogenization of the light still could use improvement with this new device.] [George]
You may enjoy numerous threads at www.bautforum.com on this topic. [George1806 12/22/05]
Woh, thanks, George! Zhatt 18:16, 23 December 2005 (UTC)

I removed an apparently dead link. *Glenn LeDrew, "The 'Real' Starry Sky". (Accessed 2/7/06) If this link is actually alive, we can easily put it back.

I don't have time at the moment to reinsert it in the various places it's cited, but someone with a few minutes might want to. Having "(LeDrew)" strewn around with no explanation is confusing, and the article is available elsewhere on the web: http://ottawa.rasc.ca/astronotes/2000/an0006p8.html

Oh- regarding the question of the green star, in very old literature Wolf-Rayet stars were sometimes called green. That is probably because of the nebulously generally associated with those stars.

theres a "* 1 = Sun." in the color table. Theres no other * in the page. What's that refering to? all the values that don't have unit?

Quick thought... it appears the percentages describing the distribution of stars of various spectral types is in error. I added the percentages up and got almost 103%.Bill McHale 23:28, 20 March 2006 (UTC)

This is probably due to truncation error, isn't it? nihil 11:11, 28 March 2006 (UTC)
I was "bold" and removed the Harvard-style LeDrew references. Then I added a {{Refimprove}} because more references are sorely needed. — RJH (talk) 22:41, 5 June 2007 (UTC)

[edit] Colour of the Sun/G spectral type

Wouldn't it be more correct if the colours were labeled peach/pink instead of Yellow? as shown in the link already cited above! The sun is "yellow" mostly because it looks like so during sunsets as it get redder with atmospheric effect. nihil 11:15, 28 March 2006 (UTC)

The article currently says "The Sun is not in fact a yellow star..." I disagree with this statement. The output of the Sun, peaks in the yellow part of the visible spectrum and therefore the Sun appears yellow. When viewed from the Earth, the brightness of the sun makes it appear almost white. It is true that there is some filtering and scattering caused by the Earth's atmosphere (incidentally causing the sky to be blue), but the Sun is definitely yellow. --Astronaut 16:41, 11 September 2006 (UTC)

If you need any further proof ask yourself what colour does any kid reach for when drawing the Sun? --Astronaut 16:42, 11 September 2006 (UTC)

Nope, the sun is white, not yellow! Said Rursus 18:11, 4 January 2007 (UTC)

I agree with Rursus. The Sun is white. It could appear slightly yellow because of atmospheric scattering, which scatters shorter wavelengths preferentially over long, so the light passing directly through the atmosphere to your eyes (but DONT look at the Sun!) has a effective spectrum slightly biased towards the red end. But it still looks white, check it yourself! (DONT look at the Sun! :) Myrrhlin 23:30, 3 April 2007 (UTC)

I also agree with Rursus, but try this. Set your monitor's Red, Green, and Blue to equal values. Then go to your Paint program and create a custom colour with these values: Red 250, Green 255, and Blue 246. This mimics solar light output across all wavelengths. Fill in the screen with that colour. Then sit back and look at it for a while.
I see a shade of white. Interestingly, the Sun's spectrum peaks in the yellow-green, which is exactly the colour reproduced; it's just that the nearly-equal presence of red and blue 'wash out' the yellow-green colour.
So, the Sun is white, and green! Try 253, 255, and 240 for a G5. Or 255, 250, 235 for a K1. Or 245, 250, 253 for an F-type. You can 'draw' stars against a black background in Paint and compare the colours. They all look pretty white. 68Kustom (talk) 03:04, 2 March 2008 (UTC)
According to the astronomical establishment, who adopt this classification system, the Sun is technically yellow. —Preceding unsigned comment added by 143.167.7.109 (talk) 12:30, 18 April 2008 (UTC)

[edit] On the colours of stars

Stars can be, and are, coloured even though they give 'full spectrum' light because their specrums include more intensity at some colours than the others. Suppose you plot a graph of intensity as a function of wavelength: the graph for the thermal radiation of a 'black body' would be a roughly bell-shaped curve, with a blunt point in the middle and a slope down on either side. The position of the maximum depends on temperature (according to Wien's displacement law). For comparatively cool objects the maximum of intensity is at a wavelength in the infra-red, intensity declines with decreasing wavelength across the visible portion of the spectrum, so the object is brighter in red than in green, and brighter in green than in blue. The result is that it looks red or orangey-pink. For very hot objects the maximum is in the ultraviolet, and the spectrum is brighter in blue than in green, and brighter in green than in red. As a result, the object looks bluish or even violet.

Remember that the peak is blunt. Even if the maximum of the intensity curve is right on the peak sensitivity of the green-sensitive photoreceptors in the human eye, the intensity is still pretty high a bit to the right and a bit to the left, where teh red-sensitive and blue-sensitive photoreceptors are most sensitive. The result is the appearance that we call 'white'. Thermal radiation never looks green.

There is an interesting page (<http://www.vendian.org/mncharity/dir3/starcolor/>) that attempts to show what colours stars of different temperatures would appear to be if they were bright enough for colour vision and if it were not for the effects of the atmosphere and other intervening media on their apparent colour. Check it out.

Agemegos 04:07, 11 April 2006 (UTC)

[edit] Luminosity classes

Hurricane Devon: The spectral type for blue stars is the letter O (oh). The luminosity class for hypergiants is the number 0 (zero). Stop making it wrong. Xihr 02:24, 26 April 2006 (UTC)

[edit] Morgan-Keenan - temperatures and subdivision

How are the classes and their subdivisions (e. g. G0, G1, ... G9) exactly related to temperatures? It would be nice to have this information in the article. Icek 17:54, 1 June 2006 (UTC)

I've talked one of the people maintaining SIMBAD's webpage,
gjasniew(at)simbad.u-strasbg.fr, in the MK system the class K5 is followed by M0 (K7 is actually an interpolation between K5 and M0). Other authors (e.g. Lee, 1984AJ.....89..702L) classify this star as M2. (the star used in that converation, "SAO 72548")
Hope this help, CarpD 8/31/06 P.S., can you put a little background about yourself, Icek.
The spectral classes are defined by spectral standard stars, chosen once-upon-a-time. The spectra are defined by the strength of characteristic spectral lines, which happen to correllate to the atmospheric temperature where those spectral lines are produced. The atmospheric temperatures can be determined by transforming star color (UBV etc.) to temperature, assuming black-body radiation by Planck's Law. Thus spectrum and blackbody temperature are determined with different methods, and thus can be correllated by comparison. I think there's not actually any strict relation between spectrum and temperature, so that any measured spectrum strictly defines what temperature the star's atmosphere actually has, but that there are broad and general correlations between mean spectra and mean temperatures. However, some day I might scan Hipparcos Catalogue, to see whether this is true ... Rursus 18:26, 4 January 2007 (UTC)

Under the MK system, the chart gives a temperature range, just says an O is Mass=60, Radius=15, Lum= 1,400,000. It is not intuitively obvious that units are solar masses, etc. Mass, Radius, and Lum should have ranges as well. Marc

[edit] Spectral Types L and T

I think they should be moved up to join OBAFGKM... though they are the new kids in town i think there is generally consensus that they don't belong in "rare spectral types". Anyone have any protests?--StarGazer5 23:45, 23 June 2006 (UTC)

And why do you think that? The vast majority of stars are not of type L or T. Xihr 07:52, 24 June 2006 (UTC)
True, but the vast majority of stars are not O or B either. I was just thinking that they are part of the main sequence now. --StarGazer5 15:38, 24 June 2006 (UTC)
No, classes L and T are not on the main sequence; they are brown dwarfs with insufficient mass to sustain hydrogen fusion, and so never make it to the main sequence at all. The main sequence is indicated by luminosity class V, anyway, not a spectral type at all. Xihr 04:00, 25 June 2006 (UTC)
A couple of questions. I had thought that the vast majority of stars were brown dwarfs; that they outnumbered "regular" stars the same way that red dwarfs outnumber brighter stars. Also, are brown dwarfs really brown? 68.170.103.85 07:24, 2 July 2006 (UTC)
There are probably not as many brown dwarfs as there are red dwarfs. Brown dwarfs are not brown, either. L dwarfs may appear as dim red and T dwarfs magenta. Both types radiate far more in infrared, as in visible ligth they're (almost) invisible.--JyriL talk 10:03, 2 July 2006 (UTC)
I already changed 'rare' to 'extended'. Also, the Brown Dwarf population is speculated to be the most, but has not been confirmed. Basis was on the local group of stars is that brown dwarf are prevalent. Thanks, CarpD 8/31/06
Without being able to produce any reference - I believe those who created the L and T classifications intended L to be a continuation on M, and T on L of course. I'll investigate if there are any stars that had been reclassified from M10 to L0, which would clarify whether this M to L continuum is accepted by astronomers. ...L8R... Rursus 20:24, 4 January 2007 (UTC)

[edit] UBV system

I have redirected UBV system to UBV photometric system. I also think that the section UBV system should be removed from stellar classification (or at least drastically changed). We can use more than 200 photometric systems to classify stars. As I understand the purpose of this encyclopedia article is a description of the well known discrete MK quantification (as opposed to continuous - logG,Teff). The UBV system should be mentioned only as one of the possible instruments. Moreoever, we have to mention that now there is three (+ FeH) or even four (+ intertellar reddening) dimensional classification. Orionus 15:43, 27 June 2006 (UTC)

[edit] Halogen

When an equally hot object, a halogen lamp (3000 K) which is white hot is put at a few kilometers distance, it appears like a red star.

I'm not sure about this. Halogen lamps (in cars, for example) seen from a few kilometers are still yellow (at least I see them yellow). Xenon lamps, which have temperature comparable to Sun's, are blue (at least I see them blue). It's quite possible, however, that if we put a large halogen lamp and a large xenon lamp into space and look at them from the Earth's surface, the halogen lamp would look red and the xenon lamp would look yellow. This is because of atmospheric scattering, which affects short light waves way more than long light waves. Thus, atmosphere shifts yellow to red and blue to yellow. However, this affects only broad spectra, e.g. black body radiation. So, if we put a large blue LED into space, it would still appear blue (albeit somewhat dim).

[edit] Change of color?

Some IP-guy change the color on the Morgan-Keenan spectral classification table, is this correct? Thanks, CarpD 9/2/06

I think there's no such thing as a correct coloration of MK types. It's usually said that [O = blue, B = blue white, A = white, F = yellow white, G = yellow, K = orange, M = red] is just a convention. My personal tests on Auriga stars and binoculars, says that the stars really look according to this scheme! This is, of course, under weak light conditions when the rod cells dominate light registration. Scaling up the light, however, the star coloration would look like about this:
* WC * WN * O * B * A * F * G * K * M

WC sample is just one star (HD092809) and thus not a reliable mean. I've not found any carbon star spectrum to compute. Also note that from F and later, there are huge variations, so that the oddball star HD122563 (F8VI) looks like * this!!

said Rursus 16:51, 4 January 2007 (UTC)

Damn, the IP user had changed the colors back to the ugly blue-to-red scheme [Now reverted!]. I had replaced the colors with the ones given in [1]. Sure, the colors are not "correct", as one can see at the star list but still they are much closer to reality.
Are Wolf-Rayet stars really purple?--JyriL talk 17:27, 4 January 2007 (UTC)
Mostly blue (the three WN:s i computed) The sole WC i computed was violet. It will take a little time to revisit and document my programs and the spectra found at VizieR service catalogues, but I made it to correctly correllate the star colors in my hack astrolab (Swedish doc only). Rursus 17:53, 4 January 2007 (UTC)
I can put up on web, translate, explain a.s.o. on request. Just request me at tomas DOT kindahl AT comhem DOT se, then. Rursus 17:56, 4 January 2007 (UTC)
and the reference What color are the stars? that you provided, was the first link that I read, when determining how to compute star colors. It's a "classic" by now. Except: colors must not be taken too seriously - the eye adapts to different light conditions by something like "natures own gamma correction". Rursus 18:02, 4 January 2007 (UTC)
Indeed. It is sad we mammals lost tetrachromacy and the far more stable color perception common to other vertebrates. The bottom line: the article should be clear in that the colors given are only suggestive and the blue/white/yellow/orange/red colors usually mentioned are not real.--JyriL talk 18:13, 4 January 2007 (UTC)

Minor comment: Rursus's example above of breakdown between spectral class and color, HD122563 = HR5270, is a very famous star, among stellar astrophysicists, anyway. It's the brightest very-metal-poor red giant in the sky, an extreme halo star. (I ought to create the article for it.) In this context, it serves as an example of the limitations of the spectral classification process. BSVulturis 20:18, 4 January 2007 (UTC)

Far later than I should have, I've begun the promised article on HD 122563. BSVulturis (talk) 22:44, 24 January 2008 (UTC)

[edit] Where are Neutron Stars on the HR diagram?

I'm sure this question will appear. I know the answer is usually stated as to far below to mention. But the question is not answered on this article. Also, this website, http://rainman.astro.uiuc.edu/ddr/stellar/evolution.html , shows a mock picture of it at the bottom of white dwarfs. Thanks, CarpD 9/02/06

If this HR-diagram is not "obsolete", it must be "based on luminosity and color", since white dwarfs don't have spectra that fits into a Sp/Lum HR diagram any more. (OK, this is a mock-up, but imagine it to be real!) Simply put: that HR-diagram seems to be approximatelly "correct". Rursus 19:18, 4 January 2007 (UTC)

[edit] Morgan-Keenan, Harvard and MKK classifications

What's the difference between Morgan-Keenan classificaton and Harvard classification? What's the difference between Morgan-Keenan classification and MKK classification? Geboy 18:06, 6 September 2006 (UTC)

Good question. I hereby raise this as a topic for CLEANUP. Rursus 23:12, 5 January 2007 (UTC)
I have added a note clarifying that Morgan-Keenan is synonymous with the Harvard classification. The MKK section does state that it refers to luminosity (emitted energy) rather than temperature (emitted color). I believe this ambiguity has been resolved. Agreed? Idsfa 03:46, 21 January 2007 (UTC)
Historically Harvard is one-dimensional (only temperature) classification. While Yerkes - MK - MKK classification is two-dimensional (temperature-luminosity) classification. Orionus 12:06, 22 January 2007 (UTC)
Umm. Did you see that Yerkes/MKK has a separate section lower down in the article? MK is not the same as MKK.Idsfa 22:55, 22 January 2007 (UTC)
Harvard one-dimensional classification scheme (based on hydrogen Balmer line strengths) was developed about 1900 by Annie J. Cannon and Edward C. Pickering. In 1943 William Wilson Morgan, Phillip C. Keenan and Edith Kellman from Yerkes Observatory created two-dimensional classification scheme for solar metallicity stars, based on spectral line intensity ratios. In the beginning this classification scheme was called MKK (from author initials). Later, in 1953, after some revisions of classification criteria the scheme was named MK (by William Wilson Morgan and Phillip C. Keenan initials). Orionus 09:37, 23 January 2007 (UTC)
Super information, but if you have a reference for it you should fix the whole article. It makes no sense to have two different sections describing different systems and calling them Yerkes.Idsfa 15:37, 23 January 2007 (UTC)

[edit] Vandalism

Class M Class M is by far the most common class if we go by the number of stars. All the red dwarfs go in here and they are plentiful; over 78% of stars are red dwarfs, such as Proxima Centauri.(LeDrew) M is also host to most giants and some supergiants such as Antares and Betelgeuse, as well as Mira variables. The spectrum of an M star shows lines belonging to molecules and neutral metals but hydrogen is usually absent. Titanium oxide can be strong in M stars. The red color is deceptive; it is because of the dimness of the star. then they poop in there pants, a halogen lamp (3000 K) which is white hot is put at a few kilometers distance, it appears like a red star. Examples: Betelgeuse, Barnard's star

Could someone more experienced with dealing with this kind of stuff please take appriopriate steps?

What? Questions:
  • Who's speaking? (example signature: Rursus 17:34, 4 January 2007 (UTC), can be created by writing ~~~~), signatures are important for identifying when the purported vandalism occurred.
  • What's the vandalism? (Screaming such a shocking accusation must be described better, please).
  • You relate quite correctly about M-class stars. Shouldn't that information then be in the article.

Said Rursus 17:34, 4 January 2007 (UTC)

[edit] 103 % stars

When I add 78% M stars, 13% K, 8% G and 3.1% F, I'm already at 102.1%. This is too big to be caused by rounding up the first three classes. Adding the other categories gets the total up to almost 103%. Because I'm not knowledgeable in the field, could someone else look up the correct numbers?

Careful. If you look closely the numbers are not saying the same thing, this may be an error on the part of the contributers.

O = ?% of stars and ?% of main sequence
B = ?% of all stars and 0.13% of main sequence
, A = ?% of all stars and 0.63% of main sequence
, F = ?% of all Stars and 3.1% of main sequence
, G = ?% of all stars and 8% of main sequence
, K = ?% of all stars and 13% of main sequence
, M = 78%+ of all stars and ?% of main sequence.

And that can't be right either (to have 78% of all stars you would need a higher % of main sequence stars). --72.140.175.249 20:01, 28 December 2006 (UTC)

I like the sheer number! What a sight it must be! Rursus 18:48, 5 January 2007 (UTC)
The reason the numbers do not add up, no matter how you look at it, is that the cited source's numbers do not add up either. The given numbers of main sequence stars add up to 824 and not 800. I have changed the fractions in the article to match.-Wikianon (talk) 00:36, 7 March 2008 (UTC)

[edit] The french Wikipedia article counts the stars differently

There it is claimed: "Les étoiles de classe M sont les plus nombreuses (température de surface : 2 600 K). Toutes les naines rouges, soit 90% des étoiles existantes, sont de ce type," which translates as: "Class M stars are most abundant (surface temperature: 2600 K). All red dwarfs, i.e. 90% of existing stars, are of this type." No further quantification of the relative abundances of the classes is made.

[edit] Cleanup added

I added the Cleanup template message, explicitly for the rendering of the References section. The list of references now has three distinct starting-from-1 numbered sequences. BSVulturis 15:59, 22 December 2006 (UTC)

I have integrated the second set of references into the first. The first two references were added in an edit that added no other text to the article, so it was impossible to link them to any assertions. I have elided them. The Kirkpatrick & Davy references were added in an edit which specifically called out their citation to support L & T spectral classes. I have linked these refs to those two sections. Are we clear to remove this cleanup tag? Idsfa 03:29, 21 January 2007 (UTC)

[edit] S - Class Stars

Do S - class stars have a common name? Other Rare types seem to have a common name (C = Carbon, W = Wolf-Rayet, T = Brown Dwarfs, etc).

They too are carbon stars (i.e. C + S = carbon stars). They just have different composition.--JyriL talk 11:15, 28 December 2006 (UTC)
Not really; "carbon stars" are generally taken by those in the field to be just the C (and R and N) stars. S stars are generally more carbon-rich than M stars, but the spectra do show oxide bands and aren't dominated by the CN and C2 bands which are the hallmark of the carbon stars. Intrinsic S stars and carbon stars are all AGB stars caught at different points in time of their dredge-up/thermal pulse processes. BSVulturis 16:54, 28 December 2006 (UTC)
D'oh, you're right. I misremembered.--JyriL talk 20:08, 4 January 2007 (UTC)

[edit] Spectral myriad mess

The page starts to get messy. I personally added MS and CS/SC spectral classes, but I think that made the text messy. So I grouped all extended classes into Hot blue emission star classes, Cool red and brown dwarf classes and Carbon related late giant star classes. The goal is of course to prepare for oversight text, and in the case of carbon stars, link to the main article carbon star which is topical for rewrite. Rursus 21:02, 5 January 2007 (UTC)

[edit] ON, OC, BN, BC

These should be added under the Hot blue emission star classes as hybrids. Rursus 21:02, 5 January 2007 (UTC)

More odd critters: ON, OC, BN and BC stars, presumably (by me) having WR-like emissions when else being O-type or B-type. There are neither OO:s nor BO:s. Examples:

  • HD 105056 - ON9.7Iae
  • HD 152249 - OC9.5Iab
  • HD 163181 - BN0.5Iae
  • HD 2905 - BC0.7Ia

Source starspectra-skiff-2005, at VisieR Strasbourg something i'll deal with it l8R. Rursus 18:47, 5 January 2007 (UTC)

Now, dealt with. I simply merged the texts of "hybrid" star classes into "hybrid sections". If You wish a more fine grained subdivision: go ahead – wikipedia is just a very early forerunner to the Singularity, and your opinion is as good as mine. Rursus 13:37, 10 January 2007 (UTC)

[edit] Erroneous star color statements in Morgan-Keenan spectral classification

Looks like the one guy writing the text haven't tried to discern the star colors himself – anyone ever having seen Arcturus (golden) knows. It's comparatively easy to estimate the star colors of the brightest stars, and one can guess spectral type with a fair degree of accuracy, such as 80% right. However, this is valid only if the light level can be elevated so that the star becomes fairly bright - an example: Capella α Aur (0mag) can be seen to be yellow without optics, but if you wish to see the color of ν Aur (4mag), binoculars 7x50 are needed!

Regarding the colors in the main type list: they're not exaggerated. Instead: the eye exaggerates the colors of stars under the real dark conditions, so that the colors in the table seem to be washed-out in comparison. Rursus 23:07, 5 January 2007 (UTC)

I should have removed the "exaggeration" part when I reverted the colors.--JyriL talk 15:44, 10 January 2007 (UTC)

[edit] Possible Origns for Hd stars

http://www.gemini.edu/index.php?option=content&task=view&id=220 I am uncertain if this is the same as HdC stars. Thanks, CarpD 19/1/07

The article is a most welcome piece of information. I cannot see whether C-Hd and HdC are the same, but in general: all new galactic odd monsters are most welcome for a cup of coffee, and the RCrB:s have been little of an enigma for a long time. Rursus 18:12, 23 February 2007 (UTC)
I've indulged myself in carbon star lore, so it seems that HdC is a heterodox TLA for what shall canonically be C-Hd. The article connects RCrB (heterodoxly termed RCB, there's something about the 3 in TLA that attracts THEM!), claiming that RCrB:s and C-Hd:s alike may be former white dwarf pair colliding and creating a certain class of supergiant stars. It's not impossible, but I'll take a look to see where the article fits. Said: Rursus ☺ ★ 08:51, 10 August 2007 (UTC)

[edit] Cleanup Tag

I removed the cleanup tag as it looks like a lot of good work went into this article in the last month! Good work everyone! Alex Jackl 06:52, 26 January 2007 (UTC)

[edit] Hypergiants as class 0 (zero)

Well, I read about them, but do not see them anywhere. Usually see them as Ia-0. This websight, THE HERTZSPRUNG-RUSSELL (HR) DIAGRAM, states of class 0 (zero), but the few examples he has, Simbad states as Ia or Ia-0 class. So, not sure about this. I think I read some class of 0 (zero) in the Astronomical Papers. But again, the examples they give, Simbad will rate them as Ia or Ia-0. Is there a chance that, we have a class 0 (zero), but have not found any stars to fit that class? Thanks, CarpD 3/12/07

[edit] Mn-type peculiar A stars

Yttrium and Mercury in Mn-Type Peculiar A Stars, did not know if this constitute as a sub-type class to A stars for this page. Thanks, CarpD (^_^) 15/3/2007

Almost certainly that's a discussion of mercury-manganese (HgMn) stars, and not a separate subclass. The terminology has settled down some since 1971 when that paper came out. BSVulturis 21:41, 27 March 2007 (UTC)

[edit] Color

Note there are several previous discussions of color above.

As of 20 May 2007, there are several problems with the article's treatment of color. Here are the problems, and the changes I just now made. 66.30.112.97 20:13, 20 May 2007 (UTC)

  1. The sentence "The common classes are normally listed from hottest to coldest (with mass, radius and luminosity compared to the Sun) and are given in the following table." cites Stellar_classification#_note-Charity. But none of the listed data is from there, only the background colors used in the table.
    • Fix: move cite. Done.
  2. "The colors in this table are greatly exaggerated for illustration." They are not exaggerated at all (see the page).
    While not exaggerated, they do represent the actual color of stellar objects, rather than their (complex) observational appearance in the sky.
    The formulation is misleading but contains some hint of the truth: if the luminosity would be greatly exaggerated, the human eyes would perceive the colors as in the table. The sentence must be reformulated.
    There's nothing such as a "true" or "actual color" of a star representation, see above! Whether observing a star by a huge telescope brightening the object to a certain light-bulb luminosity is more "normal" than observing it by naked eye under a dark sky, is a matter of taste. Said: Rursus ☺ ★ 09:18, 10 August 2007 (UTC)
    And are slightly "red-shifted" (G being pinkish rather than white, as in Image:HR-diag-no-text-2.svg
    ), because the web standard D65 white-point D65 (basically a 6500K blackbody) was used, but it is regrettably noticeably blue-ish. Perhaps a Sun as white-point should be used here instead, as graphics standards and the light emitted by s D65-calibrated CRT are rather less important here than avoiding confusion.
    • Fix: remove sentence, and expand the discussion of color below the table to include observational issues and D65. Done (but see below).
    • Possible improvement: Switch table background colors to a Sun white-point.
  3. The "Star color" column is a mess. Stellar color is for historical spectroscopy reasons described relative to Vega, which is very blue. The words used are not intended to describe the eyeball appearance of the star under any observational or hypothetical conditions.
    • Fix: If the background colors had a Sun-wp, I might suggest discarding the observational descriptions entirely. As it is, how about breaking out an "Apparent color" column, and fleshing out the color discussion below the table. Done.
    No, that "Fix" was an obfuscation of knowledge and tradition. First: Wikipedia adhers not to the truth per se – whether you deem the presented claims to be correct or not – is pretty irrelevant (unless you can refer to your own heavy research on an external site). Wikipedia adhers to the summed-up knowledge as perceived by humankind, which does not necessarily adher to truth. So unless you can make an outside reference, "factual dubiosities" shall remain here, if they are traditional. Secondly, I claim that the words used adhered to the eye impression under dark conditions. I'll have to restore the texts as it was written. Or, go out and observe the stars yourself, if you don't believe me. Said: Rursus ☺ ★ 09:32, 10 August 2007 (UTC)
  4. "While these descriptions of stellar colors are traditional in astronomy, they really describe the light after it has been scattered by the atmosphere." The italicized text is completely bogus.
    • Fix: Remove, replacing it with better discussion. Done.
  5. The "Spectral types" section says "The following illustration represents star classes with the colors very close to those actually perceived by the human eye." While there is the potential for confusion vis the other colors on the page, "perceived by the human eye" adds enormous fuzz, so it's not incorrect.
    • Fix: Ignore for now. Done.
    • Possible improvement: Explain.

The color text could use some editing, but is at least now, I believe, correct.

  • Possible improvement: Add a sentence about how the colors observed with the unaided eye differ from actual color. I don't know that this is the place for "things low in the sky look red". But I would be interested in whether it is primarily a physiologic, perceptual, or physical effect, or some particular combination. Given the web's great variety and low quality of discussion on this topic, it might be worth waiting for an unusual professional, with a special interest in the area, to weigh in.
This is not the correct way to edit Wikipedia. Provide references for your color musings. Don't draw conclusions that are not founded in some reference, or your edits will be removed according to the WP:OR Original Research criterion. Said: Rursus ☺ ★ 11:12, 10 August 2007 (UTC)
Now the color section is truly fixed, bug free, contradiction free, superfantastic and absolutely accurate, aside from errors that I leave for future fixes. But D65 correction isn't a correct way to standardize faint point light sources, keep D65 off from astronomy! Said: Rursus ☺ ★ 11:40, 10 August 2007 (UTC)
... mm, like applying EU window glass standards on telescope grinded glasses ... grumble ... mumble ... Said: Rursus ☺ ★ 12:03, 10 August 2007 (UTC)
A Review of RGB color spaces (BabelColor) - page 17 section 2.1.6, first sentence: "The eye is more sensitive to variations of luminance in low luminance levels than similar variations in high luminance levels." Said: Rursus ☺ ★ 12:56, 10 August 2007 (UTC)

[edit] Color restoration

According to tradition, and those bold guys that dare go out in the dark with binoculars to see for themselves:

SP Moore Larsson-Leander Roy/Clarke
[1] [2] [3]
W -- --
O -- Blå --
B Blue white to white Blåvita Bluish-white
A White Vita --
F White -- Yellowish
G Yellow Gula (= Yellow) Yellow
K Yellow orange Orange-färgade (= -coloured) Reddish
M Orange red Röda --
R Red Starkt (= strongly) röda Orange-Red
N Red Starkt (= strongly) röda Orange-Red
S Red Röda --
  1. ^ The Guinness book of astronomy facts & feats, Patrick Moore, 1992, 0-900424-76-1
  2. ^ Astronomi och astrofysik p125, Gunnar Larsson-Leander, 1971, no ISBN, ed 2 had ISBN 91-23-71074-8
  3. ^ Astronomy, structure of the universe p140, A. E. Roy, D. Clarke, 1977, 0-85274-082-4
Secchi Colour
I White
II Yellow
III Red
IV Very red

Feel free to add!! Said: Rursus ☺ ★ 09:43, 10 August 2007 (UTC)

[edit] white dwarf examples

On the wish list: white dwarf examples. Said: Rursus 21:35, 20 May 2007 (UTC)

try Sirius B and Procyon B. Timb66 01:56, 21 May 2007 (UTC)

The nearest solitary white dwarf would be Van Maanen's star. — RJH (talk) 22:38, 5 June 2007 (UTC)
We take those three. Thanks. Said: Rursus ☺ ★ 08:25, 10 August 2007 (UTC)

[edit] SB spectral class

I been reading some AJ papers, and when they list stars, sometimes SB, SB1, or SB2 appears for the spectral class. Did not know if SB should be listed here.

  • SB - Spectroscopic Binary
  • SB1 - Spectroscopic Binary, single lined spectra
  • SB2 - Spectroscopic Binary, double lined spectra

Also, SB1 & SB2 is not listed in the Spectrscopic binary section of the Binary star page. Thanks, CarpD, 6/11/07.

SB is not a spectral type and so should not be listed here. But single- and double-lined SBs should definitely be menioned in the Binary star page. Timb66 11:20, 12 June 2007 (UTC)

Would it warrent a not stating that it is not a spectra type. The only reason I ask is because when reading the AJ papers, it took 3 papers before some states what SB, SB1, & SB2 means. So, anyone looking up spectra type, would probably be dumb founded as to what SB was. I know I was, being an amateur to astronomy. I will leave the descision to you. Thanks, CarpD 6/12/07
I've seen some stars listed with comments about it being a spectroscopic binary in their spectral types, which can lead to confusion. Additionally, I've seen a few stars listed with composite types (where a single "star" is two or more stars with approximately equal luminosity but different spectral types). Spectral classes have often been given without as much formal rigor as one might hope, and it can be very confusing to those who aren't in the racket. BSVulturis 17:44, 27 June 2007 (UTC)

I added an entry on the page for SB. It is already on List_of_astronomy_acronyms#S. I also added a bit to the page on Binary stars. I think that should be enough? Timb66 05:49, 13 June 2007 (UTC)

[edit] Class O - one in 32000 or one in 3200000?

According to the article, about 1 in 32000 main sequence stars is of class O, but according to the table it is 1 in 3200000. Which is correct?

Discrepancy resolved, with reference. Urhixidur 18:53, 27 June 2007 (UTC)

[edit] How does this star (WR 24) fit the classification?

WR 24 (HD 93131), SIMBAD states a spectral classification of WN6ha-w…

I am guessing that ha could be Hα? Thanks, CarpD, 16/8/07.

[edit] Classification Table

Hi all. The table that illustrates the classification of stars under the Havard system does not state the units for mass, luminosity or radius. If I knew what they were I would update it myself, but unfortunately I don't. Perhaps someone who does know what they are would like to do it? HMRaven 02:40, 3 October 2007 (UTC)

Spectral classification explicitly is not intended to map to such quantities; it is done by empirical comparison among a set of standards. It turns out that for many stars in a limited way, one can interpret a spectral classification in terms of surface temperature and atmosphere pressure (which maps to surface gravity, which maps to luminosity), but there are important limits with this, and you do it at your peril. "Calibrating" spectral class in terms of temperature and gravity isn't possible with reliability. BSVulturis 17:17, 9 October 2007 (UTC)

[edit] Vandalism "치타맨"

That was weird, wonder what is problem was? Anyhow, "치타맨" is Korean for gold. Thanks, Marasama 22:27, 2 December 2007 (UTC)

[edit] Colour of F-class stars

Just thought I'd try and clear this up...an IP changed the Canopus page to describe it as a white rather than yellow-white star. I changed back as that was what I always read in books as a kis but thought this was what was meant so worte it thus to clarify. Is this an accurate appraisal, and if so can we get a ref for it? I am still a neophyte at star stuff. cheers, Casliber (talk · contribs) 12:45, 13 December 2007 (UTC)

Canopus is a F-class supergiant star and essentially white when seen with the naked eye, though these stars are considered to be yellowish-white when viewed in greater detail.

Mostly correct. SIMBAD classifies Canopus as F0IIm, but the Skiff 2007 list of star spectra gives 4 measurements: F0I (1918), F0Ia (1955), F0Iab (1957) and A9II (1989). Canopus seems to be a border case, obviously. Said: Rursus ☻ 14:33, 5 February 2008 (UTC)
Ahaaa, belated thanks for this. must update the page...Casliber (talk · contribs) 03:29, 2 March 2008 (UTC)
There's a lot of controversy around star colors, but they basically come in three flavours: blue-white, white, and orange-white. Try putting Red 248, Green 251, and Blue 255 in your Paint program. There's Canopus. Not a hint of yellow! 68Kustom (talk) 03:46, 2 March 2008 (UTC)
OK, should the Skiff reference go in the article? How much wieght does it have compared with the older ones? Casliber (talk · contribs) 03:57, 2 March 2008 (UTC)

[edit] Spectral peculiarities Example

Hi, after the table of the Spectral peculiarities, it can be read "For example, Epsilon Ursae Majoris is listed as spectral type A0pCr, indicating general classification A0 with an unspecified peculiarity and strong emission lines of the element chromium." but in this case the "p" tag doesn't correspond to the table p which is "Peculiar spectrum, strong spectral lines due to metal"

It should be "For example, Epsilon Ursae Majoris is listed as spectral type A0pCr, indicating general classification A0 with a strong spectral lines due to metal and a strong emission lines of the element chromium."

Is there a p tag in front of each of the metallic tag (Si,Mg,Cr...) ? So we can wrote : "For example, Epsilon Ursae Majoris is listed as spectral type A0pCr, indicating general classification A0 with a strong spectral lines due to emission lines of the element chromium."

--90.23.151.180 (talk) 21:57, 12 March 2008 (UTC)

Ok, I have read SkyTonight: The Spectral Types of Stars, the p tag is "Unspecified peculiarity, except when used with type A, where it denotes abnormally strong lines of 'metals' (related to Am stars)". So i'm going to update the p tag cell. But the question about p[Metallic] tag still remain, and the example is still false. --90.23.151.180 (talk) 22:18, 12 March 2008 (UTC)
Undoing the p denotion. Peculiar star, states it is mostly metals. Thanks, Marasama (talk) 07:11, 5 May 2008 (UTC)

[edit] Chemical suffixes?

After the various chemical symbols are roman numeral suffixes, e.g Fe I, Ca II, C III, Si IV. What do the suffixes indicate? Sbowers3 (talk) 07:07, 22 April 2008 (UTC)

These are spectroscopic notation for ionization states, I meaning neutral, II meaning singly ionized, III doubly ionized, etc. For example, a Si IV line is from the Si3+ ion. Spacepotato (talk) 07:23, 22 April 2008 (UTC)
Thanks. Is there a good place to add that info to the article? Before asking, I did follow some links to other articles, but did not find the answer. Sbowers3 (talk) 23:11, 22 April 2008 (UTC)