Talk:HIP 56948

Disputed
I tagged the unreferenced luminosity class value with a fact tag. This was reverted by this edit, with the comment that, "no need to cite things that are mathematically deducible — in this case, from the absolute magnitude". It may be true, but statement does not appear to be per standard Wikipedia policy. The luminosity class is also not listed in the cited references, which gives me concern that this may indicate OR. Hence I have to question the reversion. If it can be demonstrated mathematically, then a note can be added showing both the math and a suitable reference. Thank you.&mdash;RJH (talk) 21:06, 2 June 2010 (UTC)
 * How pleasant to see a fact so politely disputed! Thank you for your courtesy. My reasoning is as follows:- 1) The designation "G5V" would be appropriate if this was a class G5 star that's on the main sequence in the Hertzsprung-Russell diagram. 2) A star's position on the Hertzsprung-Russell diagram is determined its absolute magnitude.  (See stellar classification.) 3) For a class G5 star, an absolute magnitude of 4.58 would mean that it must—by definition—be on the main sequence. 4) HIP 56948 has an absolute magnitude of 4.58. Therefore (5) HIP 56948 is correctly designated as G5V. I think that the part of this reasoning you're disputing is item 4, but am I right?— S Marshall  T/C 21:39, 2 June 2010 (UTC)
 * Thank you. Yes I think #4 is my main stumbling block. (I think the luminosity class may actually be determined by the width of spectral lines.) But again, my primary concern is about the referencing, rather than the logic. None of the sources in the article actually list the luminosity class of this star, which causes my concern. What you have stated here could be considered tantamount to OR, so I think we need to be careful about the documentation.&mdash;RJH (talk) 21:59, 2 June 2010 (UTC)
 * Well, #4 is where the "mathematically deducible" part comes in. Would you be prepared to accept that (1) the apparent magnitude is 8.70, and (2) the distance is 217 light years?— S Marshall  T/C 23:08, 2 June 2010 (UTC)
 * This article claims G5V in its Table 9.1, but its citation for that is the Melendez and Ramirez (2007) article that is already cited here that does not actually state a spectral class. I expect that they are making the same step that S Marshall is suggesting, which is not unreasonable, but I don't know if this is any more satisfying to RJHall. And yes, luminosity class is determined by the width of spectral lines. That method is independent of any intervening extinction that could cause a simple calculation of the absolute magnitude from distance and apparent magnitude alone to be in error (though that is certainly not likely to be significant for a star ~70 parsecs away). James McBride (talk) 23:21, 2 June 2010 (UTC)
 * Another way of looking at it, that does not depend on any calculations, would be to accept Wikipedia's (cited) definition in G-type main sequence star, which says that such a star is one with between 0.8 and 1.2 solar masses and a surface temperature of between 5,300 and 6,000K. HIP 56948 is right in the middle of both of these ranges.— S Marshall  T/C 23:35, 2 June 2010 (UTC)
 * That is not a definition; it's rather an empirical result of the paper cited that G-type main sequence stars lie in the given range.  As far as Wikipedia policy goes, I think it will suffice to quote the reference found by James McBride (Table 9.1, p. 400, ISBN 1441916830) which states that this star is G5V.  Spacepotato (talk) 01:57, 3 June 2010 (UTC)
 * Yes that would work for me. Thank you.&mdash;RJH (talk) 15:15, 3 June 2010 (UTC)

I think it would be incorrect to use such deduced spectral types: essentially the spectral type is a classification of the star's spectrum, not a classification of the star's physical properties. The fact that there is a fairly good correlation between spectral type and various physical quantities (temperature, gravity, luminosity, etc.) probably accounts for a lot of the reasons why the spectral classification system has become so ubiquitous, but we should be wary of making the inference ourselves without references. My preference would be to only use referenced spectral types, without trying to guess bits of the classification that are not supplied. Icalanise (talk) 17:28, 3 June 2010 (UTC)
 * Perhaps a statement about this should be included in the article as clarification? Thanks.&mdash;RJH (talk) 22:24, 3 June 2010 (UTC)

Age
There seems to be confusion on the age of this star. The article says both: older than the sun.
 * a few millions years
 * about 1 Gyr = 1 billion years

And now, says it is 1 Gyr younger than the sun.

Time to sort this out? Awolf002 (talk) 17:57, 14 April 2012 (UTC)
 * Yup, that's confusing. Different sources say different things.  Since there's considerable overlap between the authors of each source, I'm tempted to follow the most recent one on the assumption that it represents improved research over the older sources.  Does anyone have any objections to replacing all references to age with the 1Gyr younger figure?— S Marshall  T/C 00:00, 15 April 2012 (UTC)
 * There having been no objections, the page was updated.— S Marshall T/C 11:55, 16 April 2012 (UTC)


 * Added, as it was unclear about the two ages:

In 2009 with a better measurement, the age of HIP 56948 was revised to ~3.5. Billion years old, Gyr.