Talk:Acrux

Smoothed it out.
I hope everyone likes it. —Preceding unsigned comment added by 68Kustom (talk • contribs) 02:45, 18 February 2008 (UTC)

Absolute magnitude
Should be almost exactly the same as Mimosa, both around -3.5 - -4, and not 0. If it were 0, then it wouldn't be a prominent star. —Preceding unsigned comment added by 154.5.221.231 (talk) 13:18, 5 January 2009 (UTC)

Halo
Some photos show Acrux embedded in an extended halo not mentioned here. Is this real or an artifact of the particular telescope or camera that was used?Virgil H. Soule (talk) 14:04, 18 February 2012 (UTC)

Brightness of components
List of stars in Crux and this article text give Alpha A and Alpha B as 1.40 and 2.09, respectively. So what are the 1.33 and 1.75 magnitudes for them in the infobox? Someone forgot to change them while changing the other? 85.76.73.19 (talk) 04:38, 2 December 2015 (UTC)
 * The infobox cites a reference for the given magnitudes. As such it is "correct".  The article text and the list need to change, unless an alternative reference can be found to support them.  Disclosure: I'm the one who edited the infobox magnitudes, relatively recently.  Prior to that there was no reference for the individual magnitudes.  Lithopsian (talk) 12:03, 2 December 2015 (UTC)


 * The list mentioned has 7 source (books?) referenced, but none are quoted on the list. There are dates on which the sources have been used, but quite hard to know without page references. 85.76.73.19 (talk) 05:54, 4 December 2015 (UTC)

What does the name 'Acrux' apply to?
I refer to my edit of 18 October - More precisely specifying the star named Acrux; consequential amendments; tidying up - which was reverted by Lithopsian the same day: Undid revision 744929327 ... it was basically right before - Acrux is both the (unresolved) Aa and Ab components of α Cru A (which is resolved from α Cru B). Basically, I think I'm right and he's wrong! :)

(A note on nomenclature to avoid confusion. I'll disregard the potential additional component - α Cru C - as it's not relevant here. That makes α Cru a triple star system with a binary pair and a single star in mutual orbit with that pair. One designation scheme is to call the binary α¹ Cru and the singleton α² Cru. Alternatively they can be called α Cru A and α Cru B. In the latter scheme, the binary's two components are designated α Cru Aa and α Cru Ab. However, if the former scheme is used, the two components should be α¹ Cru A and α¹ Cru B. I say 'should' because I haven't seen any designation of the two components starting with α¹ Cru. Not saying there aren't any; just that I haven't seen any!)

The name Acrux historically applied to α¹ Cru. The new IAU WGSN approved the name for α¹ Cru on 20 July 2016, set out in its Bulletin No.1]. This, I surmise, is why Lithopsian argues that the name Acrux applies to the binary as a whole. However in the WGSN's Bulletin No.2 it states that:


 * "In some cases, the name was historically attributed to multiple stars, however WGSN has clarified which star/component. Designations in column (2) are HR #s from the Bright Star Catalog, and IDs in column (7) are the Bayer or Flamsteed designations. Some stars listed by HR # or Bayer/Flamsteed designation themselves may be multiple. Where a component letter (from e.g. Washington Double Star Catalog) is not explicitly listed, the name should be understood to be attributed to the brightest component by visual brightness."

Acrux is listed by the WGSN as applying to α¹ Cru aka HR 4730 (α² Cru is HR 4731). However, α¹ Cru is multiple (binary). Therefore, I argue, the name should now be attributed to the brightest component of α¹ Cru - that is to α¹ Cru A/α Cru Aa only.

Comments? Cuddlyopedia (talk) 09:14, 24 October 2016 (UTC)
 * I agree with you that Acrux is α¹ Cru aka HR 4730. And of course, regardless of what we think the IAU has stated that explicitly. We should be careful about saying anything more than what the IAU says, so assigning the name to any individual component of α¹ Cru (HR 4730) is risking WP:OR. I think we agree about which dot in the sky should have the name, but perhaps some confusion in that there is no α¹ Cru A. α¹ Cru = α Cru A = HR 4730. α² Cru = α Cru B = HR 4731. α¹ Cru (= Acrux according to the IAU) is then a spectroscopic binary with components generally called α Cru Aa and α Cru Ab. Given that α Cru Aa (and Ab) are unresolved spectroscopic companions, I don't think there is any case for extending what the IAU says to apply Acrux to only one of them. I've tried to make the components and their names more clear in the article, but it may still be confusing. There is a picture here that may help - it clarifies which components the A/B/Aa/Ab (and C/D, etc.) apply to although it avoids the α¹/α² terms completely. Still slightly odd that two stars just a few arc-seconds apart get called α¹ and α², let alone that one gets a name and the other doesn't, but there you go. It would perhaps be better if the α¹/α² nomenclature had never been introduced, for example there is no such thing as α¹ Cru A, but it seems quite established.Lithopsian (talk) 13:12, 24 October 2016 (UTC)


 * Or perhaps there is no confusion and you're saying that proper names should be applied to individual components of spectroscopic binaries? Rather than just to individual components of visual binaries? Lithopsian (talk) 21:02, 24 October 2016 (UTC)
 * Hi. :) Thanks for the link to the WSC. I'll find that very useful! It certainly clarifies the nomenclature. According to the IAU-CSN, Acrux is approved as a name for the star designated HR 4730 and the table also gives HIP 60718 and HD 108248 and the ID α¹ Cru. This is what the MSC denotes as component AB with two components themselves labelled A and B (A itself as a binary with components Aa and Ab). So, it seems α¹ Cru = AB. (What's α² Cru? You'd think CD, but its HR number as given in the article implies B! ???) HR 4730 is a multiple star so per Bulletin 2 the name should be "attributed to the brightest component by visual brightness". Now there's an ambiguity as to whether the word 'component' includes sub-components or not. If not, Acrux should apply to A; if it does, Acrux should apply to Aa.
 * α¹ Cru != AB. α¹ Cru = A. Maybe the MSC page is just confusing things even more (by being wrong!). Referring to HR 4730 as AB just isn't right, shown for example by its apparent magnitude of 1.33 where the combined brightness is about 0.7. HR 4730 is A, and HR 4731 is B, as listed in the same table. Perhaps easier to follow by checking the apparent magnitudes, so is HR 4731 = B at mag 1.75 (= α² although that isn't shown at MSC) and HR 4730 = A at mag 1.33, with α Cru (as a whole), or α Cru AB to be explicit, at mag 0.7. The WDS and CCDM databases are also good for getting all the visual (and occasionally spectroscopic) components - there are handy links at the bottom of the main Simbad page. Lithopsian (talk) 13:57, 25 October 2016 (UTC)
 * Well, it certainly doesn't help if the WSC gets things wrong! But the balance of sources do indeed state that α¹ Cru = α Cru A. And it makes more sense, so we'll go with that! Cuddlyopedia (talk) 07:48, 26 October 2016 (UTC)


 * The IAU-CSN says that "The "#" after the constellation column is the component to the Bayer/Flamsteed designation, if needed (e.g. Proxima Centauri = alf Cen "C"), but may be left blank where the primary by visual brightness is unambiguous (blank = A)." For Acrux, this implies the name applies to A. However, if I refer you to comments from Eric Mamajek, WGSN Chair, in my post at Wikipedia talk:Naming conventions (astronomical objects)/Archive 1, you'll note that he says that (basically) the WGSN approves names for individual stars only, not systems. This suggests that they intended Acrux to apply to Aa. Unfortunately, they've never explicitly said so in a citable source! So, what to do? Cuddlyopedia (talk) 11:31, 25 October 2016 (UTC)
 * Well, it seems fairly clear from Eric's explanatory comments that the proper name should "technically" apply only to the brightest stellar object, seen or unseen. I can see where this will keep things clear in the future as new components of systems are discovered, but until we start landing people in some of these systems, a distinction such as between Acrux Aa and Acrux Ab ("technically" not Acrux!) seems more confusing than helpful. As pointed out, names such as Sirius B and Albireo B (for a highly visible example) are widespread and unlikely to be erased from existence by an IAU working group. As to what we do in this article, I don't know. No harm in explaining, I suppose. Lithopsian (talk) 13:57, 25 October 2016 (UTC)
 * We'll have to go with what we can cite. So, α¹ Cru is Acrux. But I'll email Eric for any comment. Cuddlyopedia (talk) 07:48, 26 October 2016 (UTC)
 * Might be best to keep it relatively straightforward here and explain all the gory intricacies in a dedicated article on stellar proper names. Lithopsian (talk) 14:02, 26 October 2016 (UTC)
 * I've heard back from Eric. The WGSN did indeed mean α Cru Aa and they've now updated the Catalog etc to reflect that. I'll update the article. Cuddlyopedia (talk) 16:25, 21 November 2016 (UTC)

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Move discussion in progress
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Absolute Magnitude is not correct.
The cited value of -3.77 does not appear in the cited source at all and conflicts with other sources, WolframAlpha has a few alternate sources: https://www.wolframalpha.com/input?i=absolute+magnitude+of+acrux Singulary (talk) 20:10, 20 October 2022 (UTC)
 * Looks like -3.77 to me. Lithopsian (talk) 20:28, 20 October 2022 (UTC)
 * That just points back to the source already cited on this article (Kaltcheva 2014). Maybe I'm reading it wrong, but where does that publication list -3.77? Singulary (talk) 11:29, 26 October 2022 (UTC)
 * I gave you a link direct to the page that shows the value -3.77. Lithopsian (talk) 18:21, 26 October 2022 (UTC)
 * Yes, I saw that. But your link, at the top of the page, points to GSH 305+01-24 stellar content (Kaltcheva+, 2014), which is source 7 in the article. Maybe I'm reading it wrong, but that source, on arxiv, does NOT mention the magnitude of Acrux. Calculating the absolute magnitude from the values given in this very article gives the value the wolfam alpha database provides. I'm just trying to understand the discrepancy. Singulary (talk) 20:20, 4 November 2022 (UTC)