Talk:Beta Canum Venaticorum

Chara

I'd like to see some verification of the assertion that 'Chara' can refer to Alpha Canum Venaticorum. As far as I can tell, 'Chara' is by tradition unambiguously Beta Canum Venaticorum. Alpha Canum Venaticorum was known as 'Asterion' until it was renamed 'Cor Caroli'.

Agemegos 02:55, 11 April 2006 (UTC)[reply]

There seems to be some historical confusion which hunting dog is named Asterion and which is named Chara and therefore the stars that are named accordingly. See the article "Asterion and Chara – the Confusion of the Chase" by Bernholz & Lyons [[1]]. Also, there are better data now from Gaia mission. Still no exo planets known for Chara, but there is Georgia State University's Center for High Angular Resolution Astronomy (CHARA) looking for exo planets. -- 2003:E5:172E:CA09:90B6:468C:8E25:8616 (talk) 09:59, 30 September 2021 (UTC)[reply]

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Mass of the star

I noticed that the value for the star's mass, 1.025 ± 0.050, is actually radius in the source.

AstroChara (talk) 14:32, 3 June 2022 (UTC)[reply]

Good catch. I've fixed it with a mass from a different paper. Lithopsian (talk) 16:33, 3 June 2022 (UTC)[reply]

Speaking about that though, I noted that the source you obtained your mass from derived stellar masses from isochrone method. As part of my own project I have plotted the masses of Chara from every paper I could find (usually on SIMBAD), and noticed that the isochrone-derived masses (11 values) are lower (0.96 ± 0.05 solar masses) than masses obtained from spectroscopy (4 values) (1.06 ± 0.05 solar masses) - and I can't help but feel that this points to some fundamental error in the isochrone models and that we should go with one of the papers that used spectroscopy instead.

The papers I have that use spectroscopy for mass are:

- https://ui.adsabs.harvard.edu/abs/1990A%26AS...85.1015M/abstract

- https://ui.adsabs.harvard.edu/abs/2005ApJS..159..141V/abstract

- https://iopscience.iop.org/article/10.3847/0004-637X/826/2/171

- https://iopscience.iop.org/article/10.3847/1538-4365/aa6d5a AstroChara (talk) 15:33, 16 March 2023 (UTC)[reply]

Well done. You've just re-derived a known astrophysics dilemma, that masses derived by different methods are inconsistent, although your numbers are statistically identical so it would be premature to throw away every evolutionary model. Masses derived from orbital dynamics are frequently even more out of step, particularly for the more massive stars, and that really is a problem. Evolutionary models obviously are models, and they are models that are not 100% based on hard physics, but include some empirical assumptions or "adjustments". Spectroscopic masses on the other hand are potentially pure observations, but they require some inputs that are not always accurately known. The radius is an obvious problem, very rarely known with real precision, but the surface gravity itself is not so much observed as calculated from its effect on spectral line shapes which is another step that risks losing accuracy. Lithopsian (talk) 15:50, 16 March 2023 (UTC)[reply]

Sounds like a good time for me to dive into these papers then. I’d like to see what different papers get for stellar radius and surface gravity, and see how much spread there is. Unless the majority of the papers have the same systematic problems, the spread could probably help me judge how accurate the spectroscopic mass is…I hope. AstroChara (talk) 16:59, 16 March 2023 (UTC)[reply]

From the papers I have, 20 of them were noted to contain information about Chara's surface gravity. Plotting them, there appears to be strong clustering among most papers around log_g = ~4.4, with 5 outliers finding way too low gravities - removing those papers cause the standard deviation to go from 0.087 to 0.032. That said, log_g = 4.4 would still result in mass consistent with the isochrone value listed in the page right now. Chara isn't a particularly old nor metal poor star - I wonder what's up here. AstroChara (talk) 02:41, 17 March 2023 (UTC)[reply]

Might be worth checking whether the "spectroscopic" masses are calculated from the radius and surface gravity or just lookups based on the spectral class. All sources should be agreed on a class of G0V, but looking at that and nothing else you'd expect a mass slightly higher than the Sun.

Looking at the four papers you list, two of them derive the mass using isochrones. A third compares masses derived purely spectroscopically and masses from isochrones and finds a 10% discrepancy! For this star, it lists a spectroscopic mass of 1.05±0.14 M_☉ vs an isochrone (evolutionary) mass of 1.00+0.05
−0.04 M_☉. That's not really statistically significant, but the overall results from over a thousand stars are significant. Like I said, old news. Lithopsian (talk) 15:44, 17 March 2023 (UTC)[reply]