Talk:Cepheid variable

1908 or 1912?

The year of the Period-Luminosity is given as 1908 in the introduction, and appears again as 1912 in Use as a "standard candle". Does anyone have a more reliable source? --Chalom 21:13, 13 July 2006 (UTC)

I originally made the change from 1912 to 1908 at least in the introduction, but it got reverted back (forward? :-)) to 1912. Anyhow, I have put it back to 1908 in both places and explained (in the article - perhaps unnecessarily at this point) about the 1912 date. I wish to adduce the specific information testifying to the date claims. Quoting from her 1908 article "1777 Variables in the Magellanic Clouds" By Henrietta S. Leavitt, H.A. 60, No. 4, on p.107 she says "It is worthy of notice in Table VI the brighter variables have the longer periods". This is a statement of a period-luminosity relationship. In the 1912 article, "Periods of 25 variable stars in the Small Magellanic Clouds" on pp.1-2 she says "A remarkable relation between the brightness of these variables and the length of their periods will be noticed. In H.A. 60, No. 4, attention was called to the fact that the brighter variables have the longer periods, but at that time it was felt that the number was too small to warrant the drawing of general conclusions. The periods of 8 additional variables which have been determined since that time, however, conform to the same law.... The logarithm of the period increases by about 0.48 for each increase of one magnitude in brightness". BTW, the "8 additional" is on top of 17 from the 1908 article. So she observes and states the relationship in 1908, was unsure about its generality, gathers further results which really gave her no new information, and re-affirms the 1908 observation along with a mathematical expression of the relationship.--Netrapt 05:52, 10 February 2007 (UTC)

Graph of relationship?

I feel this article might benefit from more discussion of the actual values of the luminosity/period relationship. Possibly also a graph showing the shape of it. Is it linear, exponential?? This small addition would add a lot to the article, I think. The section above this seems to give some info to that effect. 64.56.3.187 (talk) 03:14, 11 May 2009 (UTC)

I reviewed the history and realized that someone had deleted a large portion of the page, so I reverted it. That explains the relationship, but it could still use a graph. Now that the info is there, maybe I'll try to create a graphic 64.56.3.187 (talk) 21:13, 11 May 2009 (UTC)

Dubious

V is visual and not violet in all sources I have seen, including the hardcopy Norton's Star Atlas 1973, see page 84. V is in fact somewhat green-yellow in colour, Norton places it at 550 nm, but real instruments can use differing filter values (see Photometric system for list) from 500 to 580 (and Hubble's Advanced Camera for Surveys uses 606 nm). None could be thought of as violet. See also UBV photometric system, B-V colour and Interstellar reddening. As my correction has been reverted please could someone else either correct this or add a citation for V=violet.

84user (talk) 18:00, 13 August 2009 (UTC)

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Effect of red-shift on the use of variable cepheids

Does anyone know whether the measurements of both the apparent period and the apparent luminosity of Chepeids are corrected for the effect of any red-shift?

Even if the effect of such a neglect on the distance calculated with these measurements might be small in comparison to the already greatly different value of the Hubble constant, it might be of special importance, because - in case it were overlooked - this would provide a systematic error, and the red-shift might not have a linear relationship with the distance.

I trust every astronomer understands that redshift causes the apparent period to be longer, and the apparent luminosity to be smaller. I expect therefore that the measurements are corrected for this effect, but as I cannot find any article mentioning it, I would very much like to know for sure. Velzen5 (talk) 17:27, 15 October 2010 (UTC)

Move?

Cepheid variable → Classical Cepheid variables —

• the article pertains mainly to classical Cepheids, which are a type of Cepheid variable (see also Type II Cepheids, for example). 99.192.66.42 (talk) 23:56, 21 November 2010 (UTC)
• Object you recently rewrote the article. It should go to full WP:RM to determine whether to split the article with a new one for classical, or move the article, and create a new article at cepheid. 76.66.194.212 (talk) 06:13, 22 November 2010 (UTC)
• Object because the rationale is misleading. Anonymous IP 99.192.66.42 has rewritten some of this article, including the introduction. Cephid variable has been changed to "Classical cephids" in the introduction. This looks like some form of POV pushing. If the anonymous IP wishes to have an article on "Classical cephids" then the anonymous IP is encouraged to write one. ---- Steve Quinn (talk) 05:44, 26 November 2010 (UTC)

  Comment I removed the classical cephid variable over writes of this article by restoring to the last edit by User:Kwamikagami. I then restored the small, non-trivial, edits of other editors that followed. This move request is probably no longer appropriate. Please propose changes on talk page before attempting to re-orient an established article to some other topic. ---- Steve Quinn (talk) 04:13, 28 November 2010 (UTC)

Is there some reason not to rename the article simply to "Cepheid" (which redirects to it)? (Although I see "Cepheids" is a disambiguation page - something's not quite right here.) --Kotniski (talk) 08:41, 29 November 2010 (UTC)

• "Cephid variable" is the topic of this article, and the correct name of this type of star. I am not sure how much usage the name "Cepheid" has in our lexicon to mean this type of star. However, with "Cephid variable" it is clear what is meant. Also, I fixed the "Cepheid" redirect to go to the disambiguation page. Thanks for the heads up about that. I also added more links to the disambiguation page. ---- Steve Quinn (talk) 17:16, 29 November 2010 (UTC)

I still don't really see why we need a disambiguation page at all though. AIUI, "Cepheid" has only one meaning, namely the same as "Cepheid variable", which is a type of variable star, and has two subtypes called "classical Cepheid variables" and "type II Cepheid variables". Right? So in that case, shouldn't "Cepheid" and "Cepheid(s)" redirect straight to this page, which is the article about Cepheid (variable (star))s, and a pointer be included somewhere in this article (where it talks about type II Cepheids) that more information can be found in the separate article on that type?--Kotniski (talk) 17:52, 29 November 2010 (UTC)

Actually, I was thinking the same thing. I don't think the disambiguation page is needed - just redurect "Cepheid" and "Cepheids" to the "Cepheid variable" article. I actually almost did that, instead of adding links. If you want to go ahead and make the necessary corrections per WP:BOLD, I don't think it will be a problem. In fact, I think there is some guideline that reccomends not having a disambiguation page with only two links of similar names. That is what the disambiguation page originally had, before my editing.  :>) ---- Steve Quinn (talk) 18:53, 29 November 2010 (UTC)

"Cepheid" is the demonym for the Cepheus constellation, that is a different meaning from (1) this class of variable star (2) the classical cepheid subclass of cepheid. 76.66.202.72 (talk) 20:35, 29 November 2010 (UTC)

Thank you for the update in information, and the improvement of the disambiguation page. The disambiguation page now has a valuable purpose (or function). ---- Steve Quinn (talk) 20:53, 29 November 2010 (UTC)

• Hi Steve and Kotniski, the article as presently written refers primarily to Classical Cepheid variables. For example, the masses given in the 'introduction' (5-20 Msun) or the period-Mv and period-distance relations under the 'Period-luminosity relation section': are all related to Classical Cepheids. All the stars in the 'Example' section are Classical Cepheids. There is more than one type of Cepheid variable. There are two main groups: Classical Cepheids and Type II Cepheids, but there is also a class of Cepheid variables called "anomalous Cepheids". All these 'Cepheids' exhibit different masses, evolutionary histories, and period-Mv relations. 'Cepheid variables' is ambiguous, and at one point we must begin to make the distinction here on Wikipedia. I believe we should join efforts to ensure that is clear. I spent much time editing the article, please do not disregard that so easily, particularly since several pertinent references were added to support the information posted. I shall in the coming weeks create an 'anomalous Cepheids' section on Wikipedia, time pending. But in the meanwhile, we should honestly begin the task of getting this correct and being clear what we're speaking about. There should be a classical Cepheids section, a Type II Cepheids section, and an Anomalous Cepheids section, at the very least. There should be a main Cepheids page, a disambiguation page, that allows one to go to each of the classes of Cepheids. Whoever began http://en.wikipedia.org/wiki/Cepheid is on a good start. Hopefully this cumbersome task will be facilitated by all of us helping in a small way. —Preceding unsigned comment added by 142.177.21.25 (talk) 01:12, 30 November 2010 (UTC)

Please don't change the page. I think it would be better to split off and create a new page for classical cepheids, while this page is rewritten as a cover article for all cepheids, with subarticles for types. What you've done is specializing the entire text of the article to become classical, instead of sectionalizing it. 76.66.202.72 (talk) 03:16, 30 November 2010 (UTC)

142.177.21.25 (talk · contribs) has done extensive changes to the page, while it is under discussion here. 76.66.202.72 (talk) 03:14, 30 November 2010 (UTC)

• OK I reverted this person's revisions. ---- Steve Quinn (talk) 05:22, 30 November 2010 (UTC)

142.177.21.25 and I were talking in #wikipedia-en-help, and what he meant to say is the current article primarily talks about Classical Cephieds. What he meant to propose was that this article be moved to Classical Cephieds, and a more general article on Cephieds be written here. Best, --Alpha Quadrant ^talk 06:24, 30 November 2010 (UTC)

• The anonymous editor is free to write an article on Classical Cephids. This is a general article about Cephid Variables - this is an overview article, or summary article. It is not that person's purview to hi-jack this article to suit their own tastes. If the anonymous IP wishes to pretend to not get it, or refuses to get the point, then that is up to them WP:IDONTHEARTHAT. ---- Steve Quinn (talk) 07:22, 30 November 2010 (UTC)

I have added content and sections to make it clear that this is a summary article. ---- Steve Quinn (talk) 07:32, 30 November 2010 (UTC)

"Cepheid is a demonym for the Cepheus constellation" - is this a sourced meaning? A basic Google search turned up no meaning whatever for "Cepheid" other than Cepheid variable star. And even if such a meaning does exist somewhere, the variable star is still the Primary topic, surely? I propose we dispense with the needless dab page currently at Cepheids (or Cepheid if my move request is acted on), redirect both of those terms to this article, and simply explain in this article what subtypes of Cepheid variables exist and where the name comes from.--Kotniski (talk) 08:39, 30 November 2010 (UTC)

There is the Cepheid meteor shower[1][2] ... which shows the demonymic adjectival form of Cepheus. There's also the rules of construction for demonyms of constellations in Latin (from when in the Middle Ages all such names originated) 76.66.202.72 (talk) 05:49, 1 December 2010 (UTC)

• Hi Steve, Kotniski, and 76.66.202.72. Prior to my editing an enormous fraction of the present page already related to classical Cepheids, particularly in the introduction where 99% of it was tied to Classical Cepheids. Much of the information was unclear owing to the ambiguity of what class of Cepheid was being discussed. Again, there are different classes of Cepheids, each with their different masses, evolutionary histories, etc. Classical Cepheids and Type II Cepheids are essentially unrelated, with the former being 10s to 100 million years old, and the latter being ~10 billion years old. The masses aren't even close either, the former has between say 4-20 solar masses, and the later ~0.6 solar masses. We should avoid mixing the two types of Cepheids as Walter Baade discovered more than 70 years ago. They have little commonality beyond the historic context. For example, Type II Cepheids have more in common with RR Lyrae variables. Steve, there continue to be mistakes on your edit of the page, such as: "The stars are 5–20 times more massive than the Sun and up to 30,000 times more luminous." What stars are you referring to(?) Type II Cepheids are not 5-20 times more massive than the Sun, they are 0.6 solar masses. You are speaking about Classical Cepheids. Let's take another example, Steve, you state: "Delta Cephei is the prototype of the Cepheid variable stars". That is not true, Delta Cephei is the prototype for Classical Cepheids, not Type II Cepheids, not anomalous Cepheids, or otherwise. Type II Cepheids have their own prototypes, such as RV Tau, or BL Her, or W Vir. There are still places in the text where the type of Cepheid is not specified, but in the majority, it relates/related to classical Cepheids. A page on Cepheid variables should be a jumping point to the different classes, rather than a page merely focusing on one class of Cepheid (in this case Classical Cepheids) where its parameters and characteristics are cited as being indicative of all Cepheids. We have a good start with whomever made the disambiguation page http://en.wikipedia.org/wiki/Cepheid . We now have a Type II Cepheid page, and the information on the Classical Cepheid page was changed so to reflect the fact that the parameters which were cited are actually tied to that variable. We are making progress in addressing this entire problem. Surely we can come to a consensus on the facts. Perhaps this is what we can do, (1) the disambiguation page remains with two or three opening sentences. (2) the classical Cepheid article gets created with what I had listed before, which is essentially Steve and everyone elses article but with padded with additional references and some edits. (3) Classical Cepheid information should be added to the Classical Cepheids section, Type II Cepheid information should be added to the Type II Cepheid section. The stars are essentially unrelated in terms of age, mass, etc. (4) Perhaps a history of Cepheids is created, which talks about the about the mixing of the Cepheids in early 20th century and how that led to big problems regarding the distance scale until Walter Baade came along. I am here to help.

Cepheid is 99% of the time referred to variable stars, and not stars in that constellation. —Preceding unsigned comment added by 142.177.21.25 (talk) 13:51, 30 November 2010 (UTC)

Agreed, this article should be on Cepheids in general. 142 pointed out that the current article is primary written about Classical Cepheids. I believe that is why a page move as proposed by 142 would be logical, to preserve the edit history. A more general, historical article could then be written here. --Alpha Quadrant ^talk 19:38, 30 November 2010 (UTC)

Cephid variable is a common usage title in a lot of sources. Variations on the "Cepheid" name are Type I Cepheids, Type II Cephids, either Population i, or Population II stars, W. Virginis Cepheid appears to be sometimes interchangeable with Type II stars, etc., and etc. Some sources talk about both, some emphasize one. Hence, without some definitive sources that say these cannot be viewed in some similar or contrasting context this article is appropriate as a summary article (or overview). In addition, I created a new article entitled Classical Cepheid variables. Feel free to expound on Classical Cephid variables in this article, as much as desired.

And I agree that this article needs editing, but one thing at a time works really well. ---- Steve Quinn (talk) 05:10, 1 December 2010 (UTC)

Question

How do astronomers measure the distances to galaxies by using Cepheid variables? 222.252.101.164 (talk) 08:35, 29 November 2010 (UTC)

Cepheids are known to relate their brightness to their pulsation period. If you know the period of pulsation, then you know their brightness. As you can measure their brightness on Earth, you get the distance by the relationship between distance and brightness. (The farther something is away from you, the dimmer it appears, even though, up close, they can be very bright). It's an inverse-square law relationship between distance and brightness. So... calculating from the observed brightness and the observed pulsation period, with the period-luminosity relation and inverse-square law, you can figure out the distance. 76.66.202.72 (talk) 02:14, 30 November 2010 (UTC)