Talk:VX Sagittarii

Size

VX Sgr may even be larger than WOH G64, possibly display a size of between 1,350-1,940 solar radii, that is to say about 1645 solar radii (2,290,965,180 km). — Preceding unsigned comment added by 77.192.212.179 (talk) 17:42, 12 May 2016 (UTC)

Another tricky one. The Lockwood and Wing reference is old and there are certainly better models and calibrations available today, but I can't find anybody who has taken the trouble to observe over a full range of variations (7.5 magnitudes in the visual!) and calculation the variation in the physical parameters. However, it is not valid to just take an average of the maximum and minimum radii. That would be original research. Find a number that is quoted in a reliable reference, or at the very least can be unambiguously and trivially calculated (eg. by changing the units). In this case, an average may not be the appropriate "single number" to use even if you could find a source for it, since these types of stars are often observed near maximum and then physical data calculated for that one point in time. For example, see Mauron & Josselin, the photometry for VX Sgr is very close to maximum, giving a relatively luminous, hot, and small result. The same is true for UY Scuti, calculated to be 1,708 R_☉ from photometry near maximum light, but almost certainly different (likely larger) at other times. Lithopsian (talk) 20:37, 13 May 2016 (UTC)

1,350 - 1,940 is *NOT* 1,645. You made that number up. No matter what your basis was, if it isn't supported by a reliable reference then it can't go in Wikipedia. THE INFINITE SPACE X 18:29, 21 October 2016 (UTC)

VX Sagittari

Following comment moved here from my talk page: Lithopsian (talk) 19:50, 13 July 2016 (UTC)

Hello, this is a obsolete source, 35 years ago..other time in astronomy ;-)--Kirk39 (talk) 18:05, 13 July 2016 (UTC)

Sure. If you find a more recent one that provides the same information then you can use it in the article. As already discussed, all the more recent papers I could find just pluck single values for physical properties out of their ... err, ear? ..., often without even bothering to mention what phase of the pulsation the star was observed at. When the radius, temperature, and luminosity all vary by such large margins, that is little short of pointless. Lockwood and Wing report the temperature varying between 2,400 K and 3,300 K and luminosity of 110,000 - 190,000 L_☉. Modern papers give temperatures about 200 K higher, luminosity about double, and a radius around 1,500 R_☉ at maximum which is when it is smallest. Lithopsian (talk) 20:06, 13 July 2016 (UTC)

I know about pulsation but, look here, 1200 solar radius. Another source of..XXI century for others stars here --Kirk39 (talk) 21:31, 13 July 2016 (UTC)

What do you want to happen? You're clearly not happy with the values for the radius that are in there now. What do you think would be better? Just 1,200 R_☉ and forget the pesky pulsation? Lithopsian (talk) 21:42, 13 July 2016 (UTC)

Parralax

The parralax should be 0.64 mill-arcsec (mas), not 0.64", otherwise it would only be 5.8 ly away 2001:388:6080:6118:31F4:1179:74C1:5125 (talk) 05:26, 15 July 2019 (UTC)

Fixed. Lithopsian (talk) 15:19, 15 July 2019 (UTC)

2020 luminosity

This paper gives the star a higher luminosity of 275,000+114,000
−52,000 L_☉. Should we add it? 2A01:E0A:47A:F100:6102:3E30:39BD:CC4F (talk) 20:01, 25 August 2020 (UTC)

Probably. New research, (fairly) specific to this star. The one thing I'm concerned about is where they got their distance from. There are a couple of recent maser parallax measurements that I'm aware of, but neither of them give anything like this distance. Lithopsian (talk) 20:09, 25 August 2020 (UTC)

Never mind, I was looking at the wrong column. The distance of 1.56 kpc is what I'd expect from recent maser parallaxes. The current luminosity, from the same paper that measured the maser parallax, uses a fairly crude rescaling of luminosity values from older papers. I'd still keep the very old Lockwood & Wing value; it is the only one that takes any account of the huge range of optical brightness and temperature variation and it still produces results consistent with the most modern papers. Lithopsian (talk) 20:13, 25 August 2020 (UTC)

References

Possible extreme super-AGB star or Thorne–Żytkow object

This very recent reference states VX Sgr is most likely to be an extreme super-AGB star or even a TZO star and the most luminous AGB star at Mbol = –8.6 or 217,000+160,000
−92,000. Can we mention it in the article?

P.S. should we remove the 853 R_☉ value in the starbox. It's pretty old comparing to the 1,120-1,550 estimate from Xu et al. 2018 and not reliable enough. 2A01:E0A:47A:F100:6525:88A1:3F3D:25EB (talk) 17:58, 22 November 2020 (UTC)

It is a peer-reviewed paper dedicated to this star, or at least will be soon. I can't see any reason why it shouldn't be discussed in the article once it is published. There is already some mention in the article of the unusual properties of the star, and previous studies have suggested it could be an AGB so nothing radically new. Be careful not to take one author's view, against the massive-star consensus, as being god-given fact. Also note that the paper concludes that VX Sgr is *not* a TZO. It would certainly be good to have a more modern range of values for the temperature of the star as it pulsates. Lithopsian (talk) 19:49, 22 November 2020 (UTC)

References

That paper confirms that VX Sgr isn't a RSG/RHG, the article needs to be updated Nussun05 (talk) 19:37, 6 December 2020 (UTC)

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