Talk:Deneb/Archive 1

Archive 1

Comparison

Estimates for Deneb's radius range from 200 to 300 times that of the Sun. This is the approximate size of the Sun (right) relative to Deneb.

Unless someone can provide a reference for the ~250 solar radii figure, this image (which uses this number) should not go in the article as it is potentially-misleading. The Kaler reference uses ~110 solar radii, so I've updated the article to use that. Icalanise (talk) 17:52, 25 July 2011 (UTC)

Absolute magnitude estimate

Why is the value -8.73 given to two decimal places, while later in the text both distance and luminosity are uncertain by a factor of four? (which is almost two magnitudes). Wouldn't it be better to say "about -8.5" and leave it there? Alfio 12:14, 21 August 2006 (UTC)

I've changed the page. Alfio 22:30, 2 September 2006 (UTC)

Thanks to Hevron for changing the value for absolute magnitude in the article to match that in the Starbox sidebar, -6.95. This value would seem to be derived from the data in the 2008 Apellániz et al. article (reference 3) which gives the parallax of Deneb as 2.29 mas, but with an uncertainty of more than 10% (±0.32). This parallax value may be used to calculate a “most likely” absolute magnitude value of -6.95, but it seems appropriate to round this off to 2 significant figures, i.e. -7.0, to reflect the considerable uncertainty in distance. The value has been tweaked in both the Starbox sidebar and the main text, and the text has been reworded slightly to put somewhat more emphasis on the rather large uncertainty band of both distance and absolute magnitude. Piperh (talk) 00:15, 23 August 2010 (UTC)

(Belatedly) This 2009 paper by Schiller gives the luminosity as a whopping 196,000 and absolute magnitude of -8.38 (!) - but doesn't give light year distance in it. Would gel with a further distance and doesn't hipparcos have one somewhere of 3000 light years? Anyway, might be good to lay all the evidence out. Casliber (talk · contribs) 20:38, 30 June 2012 (UTC)

The star is far enough away that the extinction may be pretty significant. I just added a sentence to that article about extinction reducing the magnitude by around 1.8 magnitudes per kiloparsec (in the V band) for stars near the galactic plane, which this star is. In this case though, the paper linked by Casliber only gives an A_V of 0.11, so obviously YMMV. Regards, RJH (talk) 21:18, 30 June 2012 (UTC)

The paper gives a distance of 802 parsecs. I have included this in the article. You can add light years too if you want. Lithopsian (talk) 23:55, 30 June 2012 (UTC)

Dang, I missed that - I did scan the article for mention of light years....great. Casliber (talk · contribs) 23:59, 30 June 2012 (UTC)

Chesneau et al (2010:p. 9) point out that the van Leeuwen (2007) value for distance is considerably smaller at 432 ± 61 pc, which results in a luminosity of 55,100 L_☉. You might want to just list both values. Regards, RJH (talk) 21:14, 3 July 2012 (UTC)

The Schiller paper lists within it previous attempts to examine Deneb's size, distance and luminosity. I think the best approach is to read, digest and then regurgitate them in an orderly fashion on the page as I am sure they will be quite fascinating (maybe not to the detail of Betelgeuse but still a fairly interesting and long tale). I am warming to the idea of donig it myself, but am not crash-hot on the physics. If anyone is keen for a collaboration, I am - on the farthest first magnitude star....Casliber (talk · contribs) 00:47, 4 July 2012 (UTC)

Yes, it's probably worth expanding the current paragraph on the topic. Thanks. Regards, RJH (talk) 17:24, 4 July 2012 (UTC)

Rank among stars

The article states that "Even assuming the lowest estimates of distance and luminosity, Deneb is the brightest and most distant of the first magnitude stars." This is a bit misleading, since "first magnitude stars" (technically, those between 0.51 and 1.50 apparent magnitude) is a bit obscure and even lowest estimates of its distance place it closer than δ CMa, which is has an apparent magnitude of 1.83. — Aldaron • T/C 22:45, 15 October 2012 (UTC)

That line struck me too, I would guess the intended meaning is that Deneb is 1)the most distant of any of the really bright stars we can see with the naked eye - this is certainly true, it easily outstrips the other major stars -. and 2) the star with the highest absolute (real) luminosity among the first-magnitude stars, and perhaps of all stars with an apparent magnitude brigther than 1.50. With the second one here, we're talking of two different kinds of magnitude. Many of the best visible stars, such as Sirius and Vega, are potent to us because they are close, but Deneb is at least 1.200 light years away, perhaps twice as far, and is still one of the brightest, seen from earth.83.254.151.33 (talk) 00:50, 28 August 2013 (UTC)

Distance in Light Years

Why is the distance given here thousands of light years different from the one in List_of_stars_in_Cygnus and List_of_brightest_stars? Xorthan (talk) 17:52, 3 December 2008 (UTC)

To add to Xorthan's comment above, the Hipparcos star catalogue cited in the article claims a distance of 3,229ly [1], as does the Stellarium planisphere software. Clackpot (talk) 18:07, 31 May 2010 (UTC)

"Distance 802+66pc" seems to be a mistake. Possibly, plus or minus should be used. — Preceding unsigned comment added by 78.105.0.33 (talk) 13:56, 6 September 2012 (UTC)

The distance listed is way off if you try to calculate it using the parallax equation (distance = 1 / parallax). It should be closer to 430 pc. A quick Google search supported this. I have no idea where the 802 figure comes from, but it's not even close to being correct. — Preceding unsigned comment added by 209.106.183.195 (talk) 13:37, 3 October 2013 (UTC)

The distance of 802pc is not derived from the parallax. It has an inline reference that you could read if you are really interested in the details of where that number came from. Or if that is too much work, just read the article. The biggest section discusses distance estimates and the inconsistencies between them. Lithopsian (talk) 15:22, 3 October 2013 (UTC)

surface gravity (log g)

In the table of properties of deneb, what's the "log g" all about?65.130.253.244 (talk) 04:37, 15 March 2014 (UTC)

g is gravity. log(g) is the logarithm of g, an easier number to use because g itself varies over such a wide range. Supergiants tend to have low surface gravity because of their large extended atmospheres. Or if you like they have large extended atmospheres because of their low surface gravity ;) Lithopsian (talk) 20:40, 15 March 2014 (UTC)

@Lithopsian what is Earth's log g? hi (talk) 16:59, 2 May 2015 (UTC)

Surface gravity. Wikipedia is your friend. Lithopsian (talk) 20:34, 2 May 2015 (UTC)

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GAIA result is speculation

The following text has been removed, mostly as it is just speculation. Worse, the source does not mention Deneb and the parallax measure won't apply as the star is brighter than the limit G<3 (less than 3rd magnitude.) Deneb is 1st magnitude.

"The Gaia satellite should provide distance measurements at least two orders of magnitude more precise than Hipparcos and resolve many such questions. The mission did not plan to observe stars brighter than magnitude 5.7, but better than expected performance and special measurement techniques are expected to enable coverage of brighter stars including first magnitude objects such as Deneb."

For this to be added the statement needs a better proof, as nether of the given references by Turon et al (2000) and Prusti (2016) say this at all. GAIA will unable to give Deneb any parallax results as the statement claims.

Note: Deneb is a prototype of ACYG variable stars. It is not that "Deneb is the prototype of the Alpha Cygni type (ACYG)" but it is the brightest example of ACYG's know. Edits changed this context, as did several other changes. Arianewiki1 (talk) 22:51, 31 March 2019 (UTC)

Just because you don't like what a reliable source says doesn't make it speculation. Lithopsian (talk) 14:19, 1 April 2019 (UTC)

Wikipedia is not a crystal ball, but worse the source doesn't say this as fact. The source actually says for this criteria that "G<3" G is less than 3 magnitude. Deneb it brighter than 3G magnitude. Hence, the statement is false. (Deneb does not appear in either source.)

As for "Just because you don't like…" is not relevant at all, as what I feel or think doesn't change the fact that it is an incorrect statement. So either prove it, or the offending text can be rightful removed. The burden of proof is yours. The onus to achieve consensus for inclusion is on those seeking to include disputed content. Continuing to add this text will be responded with the tag 'failed verification'. Arianewiki1 (talk) 21:52, 1 April 2019 (UTC)

Evolutionary state

This section has the following paragraph: "Stars evolving red-wards for the first time are most likely fusing hydrogen in a shell around a helium core that has not yet grown hot enough to start fusion to carbon and oxygen. Convection has begun to carry the products of fusion up to the surface, but these are not visible. Post-red supergiant stars are expected to show those fusion products at the surface due to stronger convection during the red supergiant phase and due to loss of the obscuring outer layers of the star. Deneb is thought to be evolving redwards, although current models do not exactly reproduce the surface elements showing in its spectrum.[24]"

In one sentence, it is asserted that the fusion products brought to the surface by convection can't be seen. In a later sentence, it is said that models can't reproduce the surface elements that are seen in spectra.

This appears to be somewhat contradictory, so I'm wondering if the point can be clarified. Attic Salt (talk) 13:08, 2 April 2019 (UTC)

I probably wrote that. Or maybe not. One sentence says that fusion products cannot be seen at the surface during redward evolution, but are expected to be dredged up during the red supergiant stage and seen in post-red supergiant blue stars. No contradiction, but you might want to read the reference for confirmation that this description is supported. Also check the follow-up to that paper, which proposes a resolution to the CNO puzzle. Lithopsian (talk) 14:38, 2 April 2019 (UTC)

Introduction 'Variable star' is not relevant

This edit[2] that is based on a illogical premise. Again, while Deneb might be a variable star, it is trivial fact about it. Deneb is a bright first-magnitude star in Cygnus. That is what it is known for. My dictionary says "the brightest star in the constellation Cygnus, a yellow supergiant."

This User is similarly arguing this on Rigel and in this thread here.Talk:Rigel#First couple of sentences in lede (It is an example of WP:POINTy behaviour.) Arianewiki1 (talk) 23:58, 26 April 2019 (UTC)

A Commons file used on this page or its Wikidata item has been nominated for deletion

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Stellar parameters

It is surprising that the distance and other derived stellar parameters for Deneb are not based on the 2007 Hipparcos reanalysis or subsequent journal articles based on this astrometry data. Instead the citation is to a journal article (Schiller and Przybilla 2008) whose distance estimate is based on Humphreys 1978, a now quite old set of estimates of distances to OB associations. There is no good scientific reason cited for this choice. The reference to the distance controversy for the Pleiades seems quite irrelevant to Deneb and indeed many other Wikipedia articles do cite the Hipparcos reanalysis data as the source for stellar distance data.

I recommend that this article use a Deneb distance of 433 parsecs, derived directly from the Hipparcos reanalysis value for Deneb of 2.31 mas — Preceding unsigned comment added by Galaxymap (talk • contribs) 20:46, 29 January 2020 (UTC)

Merely being based on a more recent analysis of old data does not necessarily make the Hipparcos re-analysis the preferred source for any particular object, that's often the case with results that are in tension with previous work. There has actually been very little in the way of published research on this topic in the intervening years. I would however point to this article, https://arxiv.org/abs/1007.2095, which with full knowledge of the discrepancy between Schiller and Przybilla 2008 and van Leeuwen 2007 used the stellar parameters for Deneb based on Schiller and Przybilla 2008. ChiZeroOne (talk) 16:18, 9 February 2020 (UTC)

The Hipparcos parallax could be left to calculate the distance in the starbox, although it would be inconsistent with the data in the rest of the starbox. The starbox can only really support one distance, so anything beyond that needs to be explained in the body. There is a paragraph devoted to this in the body and I suggest this is the place to start changing the emphasis on which distance should be preferred. Although original research is not acceptable in Wikipedia, there is still scope for picking which published research is given preference. As for calculating what other data "should" be based on the Hipparcos distance, that wouldn't be allowed. Have to find someone else who has done the calculation and use their values. Peer-reviewed papers are highly-preferred for this sort of primary data, although other reliable sources can be used. Lithopsian (talk) 17:05, 9 February 2020 (UTC)