Talk:Cepheid variable

message: 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)
replies: text: I originally made the change from 1912 to 1908 at least in the introduction, but it got reverted back (forward?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)
thread_title:  1908 or 1912? 

message: 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)
replies: text: 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)

text: "I fEeL tHis ArTiclE miGht beNeFit frOm MoRe discUsSion of tHe aCtuAl vaLues-" 🤓 stfu nerd 2.139.194.5 (talk) 13:32, 8 April 2024 (UTC)
thread_title:  Graph of relationship? 

message: 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)
thread_title: Dubious

message: 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)
thread_title:  Effect of red-shift on the use of variable cepheids 

message: How do astronomers measure the distances to galaxies by using Cepheid variables? 222.252.101.164 (talk) 08:35, 29 November 2010 (UTC)
replies: text: 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)
replies: text: That would be helpful to include in the article. That was the question I had when I came to the article, but did not find it, despite their use in measuring distance being mentioned multiple times throughout the article. — al-Shimoni (talk) 06:50, 13 January 2011 (UTC)
thread_title: Question

message: 68.188.203.251 (talk) 12:20, 8 May 2013 (UTC)
replies: text: She is mentioned in the article, in the history section. We also have an extensive article about her: Henrietta Swan Leavitt.--agr (talk) 12:26, 8 May 2013 (UTC)
thread_title:  Discoverer Omitted 

message: After reading the two articles, I'm having trouble distinguishing a Cepheid variable from a pulsar.   As I understand it, they both blink, but a CV frequency can be directly related to it's brightness (Pardon my terminology).   Could one of you Astro-folks help me out please?  Pb8bije6a7b6a3w (talk) 15:55, 14 May 2013 (UTC)
thread_title:  CVs vs. Pulsars 

message: This excellent animated .gif shows RS Puppis oscillating brightness over a five week window.
I believe this to be a public domain image, but someone should track down the actual source.
http://www.theatlantic.com/infocus/2013/12/2013-hubble-space-telescope-advent-calendar/100637/#img22  — Preceding unsigned comment added by 64.131.193.65 (talk) 23:05, 22 December 2013 (UTC)
thread_title:  Animated GIF? 

message: Could someone please re-phrase this sentence to make it more scientifically accurate and clear "undergo pulsations with very regular periods on the order of days to months".
Kind Regards
Joe  — Preceding unsigned comment added by 130.209.157.26 (talk) 15:14, 22 January 2014 (UTC)
thread_title:  Type 1 cepheid variable star - Re-phrase 

message: The wiki page on Harlow Shapley states that he used RR Lyrae stars to find the center of the Milky Way, this article, under History states Cepheids.  Which is it?  — Preceding unsigned comment added by 209.129.164.8 (talk) 23:37, 22 April 2014 (UTC)
thread_title:  Shapley used Cepheids or RR Lyrae? 

message: Substituted at 11:10, 29 April 2016 (UTC)
thread_title: Assessment comment

message: Going to need to update this section with the new Gaia stuff.©Geni (talk) 21:30, 14 May 2018 (UTC)
replies: text: Going to need to update a lot of sections with Gaia DR2 results.  So far, I've only seen one paper about Cepheids, and another about RR Lyr variables, but it was a bit vague about the resulting distance scales.  Also, there are some questions about the ultimate accuracy of DR2 parallaxes with one paper reporting systematic errors of around 80 micro-arcseconds.  We can always quote published papers though, as soon as there are any.  Lithopsian (talk) 14:51, 16 May 2018 (UTC)
replies: text: Well this paper will be able to give us some raw numbers that we can mention when it gets through peer review. Is this the one you are talking about with regards to systematic errors?©Geni (talk) 16:36, 17 May 2018 (UTC)
thread_title: Uncertainties in Cepheid determined distances

message: The article defines Cepheid variables and their subtypes in terms of their innate structure: "a type of star that pulsates radially", "4–20 times more massive than the Sun,", etc. It is not clear from the article what makes them observationally distinct from other variable stars, given that star mass and radius are not directly observed. Nor is it clear from the article when they were first defined as a separate class of variable stars. Barnyard fowl (talk) 05:35, 27 July 2019 (UTC)
thread_title:  What distinguishes a Cepheid from other variable stars? 

message: This section includes the following:
:...Now, since the surface gravity is related to the sphere mass and radius through the relation:
: g = k' \sqrt {R^3} M = k \,\sqrt \frac 1 \rho
This is surely wrong, and does not give the quoted result. I believe it should say something like:
: g = k' \frac M {R^2} = k' \frac {RM} {R^3}  = k' R\rho
This then gives the quoted result when substituted. If I do not receive any objections, I will make this update. FredV (talk) 15:47, 30 September 2020 (UTC)
replies: text: Definitely wrong.  I have already added a reference for (effectively) this derivation.  Lithopsian (talk) 16:00, 30 September 2020 (UTC)
thread_title:  Pulsation model section errors 

message: User:Drmwave commented in the article text: Warning: Figure-"Light curve of Delta Cephei...", uses a duplicate of the 0-1.0 phase data as the 1.0-2.0 phase data. This is bad. Please find a better example.  Dgorsline (talk) 12:50, 12 April 2021 (UTC)
thread_title:  new section