Where is VY Canis Majoris?

[chris]

don't worry, our "physics expert" Hank knows the answer

This condescending tone adds nothing to the discussion. One doesn't have to be a practicing physicist to understand this issue.

--Chris

[t00fri]

One doesn't have to be a practicing physicist to understand this issue.

--Chris

With that I certainly agree. But you must also grant me the professional ability to judge when someone has NOT understood this physics issue and YET continues to produce "hot air" posts. This was not the first time and at some point my patience is simply exhausted. Sorry for this.

Presumably the values used would have a reasonable scientific basis, which would be clearly documented.
....
Variable stars in general is an area where Celestia might be improved.
...

From what I could read from Hank so far, I have serious doubts that he has deeper insight into stellar evolution theory. Despite his many posts, I think he is indeed unable to constructively contribute to the ongoing /physics/ discussion, whether or to which extent a "jigger factor" approach could be justified on a more or less scientific basis.

Bye Fridger

[ajtribick]

Well, since no-one's definitively come out and stated that there are no simple relationships between the empirical radius (e.g. as provided in the CHARM catalogue) and blackbody radius, I don't see what's wrong with Hank suggesting that there might be one.

All we've had so far is Grant saying he personally doubts one exists. That's a lot different from saying there isn't one, so I really don't see why the attack on Hank is justified AT ALL.

---

Going to what is hopefully a more constructive suggestion than all this tedious ad hominem stuff: Maybe Celestia could implement the angular diameters from, say, the CHARM catalogue? That way we're using actual measured radii rather than "fudge factors".

[selden]

I think perhaps the problem is a misunderstanding of the meaning of a phrase of not-quite colloquial English. "Presumably..." means that Hank has been persuaded by past experience that there would be some astrophysical justification for whatever tabular values are provided for use in Celestia. It would be inappropriate to call them "jigger" values, for example, because they would be lookup tables with entries corresponding to appropriate (documented) fits to the published data.

STC catalogs with explicit Radius values for many of the stars known to be problematic seems like it could be a reasonable solution: the CHARM catalog only lists about 200 stars, for example, so it wouldn't introduce a significant increase in startup time. A "reliability" indicator could be incorporated in the Stellar Class display of those stars, with no need to modify Celestia.

And I think he's right about the need for support for variable stars. If some underlying mechanism is not available, whether or not it's actually used or efficient, that lack will continue to be used as excuse not to create the catalogs for Celestia.

One possible solution to the octree reorganization problem caused by varying visibility might be to store them as if they always had their brightest values. It's not as if there would be a large number of variable stars or supernovae introduced at any particular level. The largest catalog of Cepheids found during a very quick search of Vizier had only slightly more than 1000 entries, which surprised me. I'm sure I must have overlooked some larger catalogs.

p.s. The AAVSO claims that there are somewhat more than 30,000 variable stars known. Presumably the number with known distances is much smaller.

[t00fri]

Well, since no-one's definitively come out and stated that there are no simple relationships between the empirical radius (e.g. as provided in the CHARM catalogue) and blackbody radius, I don't see what's wrong with Hank suggesting that there might be one.

But without presenting any physics arguments for such a suggestion, it's "hot air" isn't it? By merely arguing with "numbers of users",

I think many users would find that approach preferable to the simple black-body calculation currently employed.

we can't reinforce any physics issue, can we?

Since I know about Grant's remarkable background in these matters, a corresponding global statement by him about the relevant problematics is on a quite different footing. Similarly with Cham and others like yourself.

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However, if --as Selden analysed above-- the misunderstanding is again due to subtle facets of English ("presumably") then I certainly apologize!
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The underlying physics problem is that according to stellar evolution theory, stellar properties depend on a variety of important parameters while the blackbody stars do NOT. Examples are e.g. metallicity, which is related to the "generation" of the star wrto its formation history. So the proposed "jigger factor" approach for star radii necessarily must assume a considerable independence from such characteristics like metallicity etc. Of course, it is known that e.g. metallicity is rather similar for Main Sequence stars. But what about all the others??

That's where I would have liked to read more constructive input/proposals from knowledgeable people...

Bye Fridger

[t00fri]

Here is just one paper that I am aware of, which presents analytical formulae for the characteristic star properties including Radius, as functions of Mass M and Metallicity Z.

http://www.citebase.org/fulltext?format ... %2F0001295

The discussion in this paper (and many others) could put our task on a somewhat more concrete footing (physicswise!)

Bye Fridger

[ajtribick]

Problem is, the models of stellar evolution aren't particularly good for red dwarfs, e.g. from the abstract of this paper about Gliese 436:

the radius is 10% larger than predicted by the standard models, in agreement with previous results from well studied double-lined eclipsing binaries.

Therefore if we tweak the radii we can't rely on theoretical models at the lower end of the main sequence, and as you said there are other parameters to take into account. (Furthermore, doesn't the bolometric correction itself depend on metallicity?)

This is why I suggested using CHARM (and/or other such sources) - it sidesteps the whole issue of just how to incorporate all these factors into a model (which seems to require detailed stellar evolution simulations) and gives measured radii.

[hank]

One doesn't have to be a practicing physicist to understand this issue.

With that I certainly agree. But you must also grant me the professional ability to judge when someone has NOT understood this physics issue and YET continues to produce "hot air" posts. This was not the first time and at some point my patience is simply exhausted. Sorry for this.
...
From what I could read from Hank so far, I have serious doubts that he has deeper insight into stellar evolution theory. Despite his many posts, I think he is indeed unable to constructively contribute to the ongoing /physics/ discussion, whether or to which extent a "jigger factor" approach could be justified on a more or less scientific basis.

Fridger,

It is not for you to judge who can contribute constructively to the discussion here. Your continual personal attacks on other forum members are not helpful. Please refrain.

- Hank

[Fenerit]

Just my one cent in this debate. Be caution with the simbol "?" because I've read in some posts how does shows itself in the descriptions when someone compile the program from CVS and the things goes wrong, so it could be matter of confusion to distinguish the good from the bad without a very visible explanation about of it.


"Presumably" in Italian is "Presumibilmente" (note the affinity) and mean "with a good probability" or "what of which is suppose that...".

[Joey P.]

Here is an addon that actually includes this star along with several larger and smaller ones (It is now 1,420 solar radii):

[Danny Lorraine]

well , there is an addon in the celestia motherlode that includes VY Canis Majoris but it ' s radius is short by 100 solar radii .
is there any way the radius can be increased ? thanks .

[FarGetaNik]

Danny Lorraine, as far as I know Celestia calculated stellar radii by itself out of luminosity and spectral type. You can manually edit the .stc of the addon and include the command

Code: Select all

Radius <km>


[Danny Lorraine]

oh really? that's how 2100 for VY Canis Majoris was calulctaed

Added after 5 minutes 26 seconds:
hey , look at this video :

phpBB [media]

it shows mu cephei to be 3870 solar radii, which is too big . mu cephei is 1420 solar radii
also it shows a star called "vv canis majoris" which is 7720 solar radii.
now celestia has even more errors

Added after 1 hour 58 minutes:
@FarGetaNik but how can i edit the sizes of existing stars ? betelgeuse antares and vv cephei a are too small, and mu cephei is too big. thanks

[FarGetaNik]

Danny Lorraine, I've never worked with star catalogues in Celestia so I'm not exactly sure how to edit star sizes. Celestia differenciates between solar system catalogues (.ssc) and star catalogues (.stc). I hope this unnecessary complication gets removed at some point since Celestia tends to ignore commands that are ussually asssiated with one catalogue type in the other one.

Usually I would use this in a .ssc file to edit a planets parameter, i. e. its radius:

Code: Select all

Modify "Planet" "Star"
{
   Radius   <km>
}


I have no idea how Celestia wants an stc file to me modified, you may just try an analogous definition in an .stc file specifying only the star

Code: Select all

Modify "Star"
...


[selden]

There are two separate threads about this same topic, which seems to be causing some confusion. Please see the post at viewtopic.php?p=138578#p138578 It explains how to use Modify to specify an updated Radius for any Star.

[Danny Lorraine II]

anyway, right now i am focusing on making textures for the largest known stars addon, as they appear in this animation :

phpBB [media]

[Gurren Lagann]

Your sources are from 2009-2012, now they had been disproven.

[Danny Lorraine II]

@Gurren Lagann
no. VY Canis Majoris is much larger . uy scuti does not exist and VY Canis Majoris is 2.924.000.000 k m s

[Gurren Lagann]

You are absurdly wrong!

http://its740.blogspot.com.br/2018/02/uy-scuti-biggest-star-in-universe.html - February 2018 source for UY Scuti
https://upcosmos.com/vy-canis-majoris/ - April 2018 source for VY CMa

[Danny Lorraine II]

uy scuti doesn't exist . now be quiet !

Added after 1 hour 20 minutes:
even if uy scuti exists , 1.708 < 2.100 .