Increase the size of galactic and star bases

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LukeCEL
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Post #21by LukeCEL » 26.03.2019, 06:24

The main source, Steinicke's NGC/IC catalog, is probably fine. However, I'm having trouble tracking down the supplementary sources. There might also be newer sources for nearby galaxies.

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Art Blos M
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Post #22by Art Blos » 26.03.2019, 06:40

LukeCEL wrote:The main source, Steinicke's NGC/IC catalog, is probably fine. However, I'm having trouble tracking down the supplementary sources. There might also be newer sources for nearby galaxies.
I am very worried about how the tool calculates the orientation of the galaxy relative to the Earth. Or was the necessary information in the source?
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Post #23by LukeCEL » 27.03.2019, 20:01

Art Blos wrote:I am very worried about how the tool calculates the orientation of the galaxy relative to the Earth. Or was the necessary information in the source?

The tool takes the inclination and position angle of the galaxy. Those two are enough to position the plane of the galaxy, but you need a third parameter so the individual arms are in the right position. I don't think there is a standardized way to note this.

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Post #24by Art Blos » 28.03.2019, 07:32

LukeCEL < I discovered the current location of the base from which our 10 thousand galaxies were taken. The old address is unavailable since 2007. May be helpful.
https://ngcicproject.org/
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Post #25by LukeCEL » 28.03.2019, 21:17

Not sure if this is the right link, I found http://www.klima-luft.de/steinicke/ngcic/ngcic_e.htm which has a download link for an XLS file. But I'll still look for more sources, especially related to distances and other properties.

Also, a bit off-topic, but a bunch of my add-ons finally got updated at the Motherlode! (See this page)

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Post #26by Art Blos » 29.03.2019, 05:18

LukeCEL wrote:Not sure if this is the right link
This is the same site that was listed in the original file with the galaxies. The old one is accessible only from the web archive, and by the name of the project I managed to find out where it moved. The appearance of the main page has not changed since.
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Post #27by norinonoroi » 07.06.2020, 01:12

I'm new here (just made an account), but I have experience working with the Gaia DR1 and DR2 data releases. What kind of information do you need to include a star? Right Ascension, Declination, distance (from parallax), magnitude, etc? And what kind of limits would you think are reasonable for including a star? distance, magnitude, absolute magnitude? Gaia DR2 has 1.1 billion stars with distances that can be calculated (though large error bounds), I doubt you want them all.

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Post #28by SevenSpheres » 07.06.2020, 02:11

norinonoroi wrote:What kind of information do you need to include a star? Right Ascension, Declination, distance (from parallax), magnitude, etc?

Yes, those and spectral type. The issue though isn't getting the data into a file, but that Celestia only supports HIP and TYC catalog numbers and has issues with loading very large star databases. One of the developers, pirogronian, has been doing some work toward supporting more and larger star catalogs in Celestia (relevant thread); if you know C++ programming we'd be glad to have you help!
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Post #29by Joey P. » 07.06.2020, 02:48

If you aren't aware, we've got a new largest star now, Stephenson 2-18 with a diameter of over 3 billion kilometers. You might want to consider adding it to databases that don't include it yet.
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Post #30by Eric Nelson » 07.06.2021, 04:27

Lafuente_Astronomy wrote:As you can see, its Radius size is at an impossible 3900 Rsun! If I remember, the actual largest discovered star, UY Scuti, only has a radi of 1800+Rsun. So, this one had to be the wrong size for the star.
UY Scuti's currently estimated to be 1708 Rsun actually, which's a bit smaller than 1800, though if you add the 192 Rsol margin of error, that adds up to 1900 Rsol.

Plus I actually made a file for Stephenson 2-18 via: viewtopic.php?f=6&t=20398&p=153995&hilit=red+supergiant#p153995

Eric Nelson wrote:"Stephenson 2-18:St2-18:Stephenson 2 DKF 1:RSG2-18"
{
RA 278.61981743236
Dec -6.51053569661
Distance 18900
SpectralType "M6"
AppMag 7.150
Radius 1496400000
UniformRotation
{
Period 30360
}
InfoURL "https://en.wikipedia.org/wiki/Stephenson_2-18"
}

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Post #31by Lafuente_Astronomy » 09.06.2021, 14:23

Eric Nelson wrote:UY Scuti's currently estimated to be 1708 Rsun actually, which's a bit smaller than 1800, though if you add the 192 Rsol margin of error, that adds up to 1900 Rsol.

Plus I actually made a file for Stephenson 2-18 via: viewtopic.php?f=6&t=20398&p=153995&hilit=red+supergiant#p153995

That comment was made back when UY Scuti's size was still at the old one. Now I know that it has been heavily reduced thanks to more accurate measurements courtesy of GAIA.

What's to say that eventually, Stephenson_2-18 might get the same treatment

P.S accidentally edited your comment, having almost forgotten the quotation button. I fixed it to what I remembered I saw, though you can make some edits to it if you think it wasn't fully fixed
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Post #32by Eric Nelson » 09.06.2021, 17:36

Then it was reported the GAIA parallax is unreliable for the measurements due to a very high level of astrometric noise until improvements in observations are made in the future.
More information on the Gaia parallax here: https://doi.org/10.1051%2F0004-6361%2F201833051

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Post #33by Lafuente_Astronomy » 09.06.2021, 21:40

Eric Nelson wrote:Then it was reported the GAIA parallax is unreliable for the measurements due to a very high level of astrometric noise until improvements in observations are made in the future.
More information on the Gaia parallax here: https://doi.org/10.1051/0004-6361/201833051

Maybe that's why GAIA has 4 Data Releases, and would be observing the same objects several times, each time more accurate than the last. And of course, if I remember, ESO has been planning a GAIA successor for sometime now
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Post #34by Eric Nelson » 10.06.2021, 02:43

Yup, and once those GAIA data improvements are made, we can finally analyze the same objects (including UY Scuti) more accurately with a method that doesn't involve too much astrometric noise.
Then we would even measure other stars and such and calculate their sizes and distances with less error.

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Post #35by Sirius_Alpha » 10.06.2021, 20:24

And of course, if I remember, ESO has been planning a GAIA successor for sometime now
There are no firm plans for a Gaia successor as far as I know. The idea has been floated, and I think we would all love to see that, but there might be some benefit to waiting a bit because

a) Astrometric solutions must take into account the orbital motion of Earth and the proper motion of the star. On numerous occasions already, the baseline between the Hipparcos measurements and the Gaia measurements (multiple decades) have allowed for the proper motion to be well-enough constrained to simplify orbit fitting for some known exoplanets - β Pic b comes to mind. A future follow-on mission will be able to take advantage of an extended Hipparcos+Gaia baseline, the further into the past that extends, the more precise the proper motion can be determined with data from a new Gaia-successor.

b) Giving a few decades of technological development can allow a Gaia successor to be as powerful an advance over Gaia as Gaia was over Hipparcos. Gaia is expected to identify tens of thousands of intermediate-period giant planets in the solar neighborhood. Maybe the next all-sky mapping mission can do the same for Earth-mass planets.

c) Funding. Given both (a) and (b), the longer you wait, the better the argument for a follow-on to Gaia becomes to the organizations from whom you would need funding to fly it.

So while there are no firm plans for a Gaia successor at this time, I would be fine with waiting until the 2040s to see one. Tying this back to the purpose of the thread, Gaia will be the standard for the foreseeable future, so we should be content to base our star catalogues off of either Gaia, or Gaia-corrected TYC+HIP database (as our wonderful A. J. Tribick is doing).
Exoplanet nerd. I maintain a monthly-updated exoplanet catalogue here:
https://celestia.space/forum/viewtopic.php?f=23&t=18705

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Post #36by Eric Nelson » 18.06.2021, 05:23

Now remember aside from UY Scuti whose parallax values of 0.6433 +/- 0.1059 mas (milliarcseconds) by GAIA 2 as the extreme astrometric noise took over, while other stars are given highly constrained parallax measurements by GAIA, stars like VY Canis Majoris were given meaningless values by the same tool such as −5.92 +/- 0.83 mas which's meaningless as opposed to the reliable measurements of 11.3 +/- 0.3 mas (implying a distance of approximately 3,82 kpc/kiloparsecs, a radius of at least 1,420 +/- 120 x Sol's and a luminosity of 270,000 +/- 40,000 x Sol's) as measured by the VLT (Very Large Telescope).

Yet NML Cygni was also given a GAIA 2 measurement of 1.5259 +/- 0.5677 mas as a result of the extreme data noise unlike SIMBAD's parallax measurement of 0.620 +/- 0.047 mas which indicates a distance of 1.61 kpc.

MY Cephei's generally measured to this day at 3 kpc (parsecs) from Sol, implying a luminosity of at least 129,000 x Sol's and a radius of at least 1,134 x Sol's radius whereas GAIA 2 gave it a "measurement" of 0.9284 +/- 0.1404 mas, meaning a distance of 1.071 kpc, a luminosity of at least 10,000 x Sol's and a radius of 363 x Sol's based on a temperature of 3.025 +/- 213 K.

Mu Cephei's was claimed by GAIA 2 to be 940 pc while the spectral energy distribution (SED) measurement in 2019 estimated a distance of 641 + 148 - 144 pc (implying a luminosity below 140,000 x Sol's and a radius of 972 +/- 228 x Sol's). Yet the bolometric luminosity summoned by all wavelengths is calculated by SED at 269,000 x Sol's on average also came with a radius value of at least 1,259 x Sol's though an estimate based on its angular diameter and assumed distance of nearly 736 pc indicated a radius up to 1,650 x Sol's.

The angular diameter from VV Cephei A (at the VV Cephei binary system) was measured with photometric methods calculated at 0.00638 arcseconds, indicating up to 1,050 x Sol's radius based on orbital timings, through earlier analysis from eclipses with VV Cephei B which currently measures up to 25 x Sol's radius.
Though much older analysis estimated it to be between 1,200 and 1,900 x Sol's radius.
Yet many techniques to this day measured the distance of its barycenter to be 1.5 kpc from Sol though both the Hipparcos and Gaia 2 parallax measurements claimed its distance to be under 1 kpc.

All this shows us how things like astrometric noise and other stuff have profound effects on data and measurements in general and some instruments have too much noise to be considered reliable even to this day.
The amount of astrometric noise in data shouldn't go past a certain level and GAIA 2's data is such a case of methods with noise levels beyond limits.

Besides Celestia also bases its stellar data from many sources.

Hope I didn't rain too much on anyone's parade with this.
Last edited by Eric Nelson on 30.07.2021, 21:11, edited 2 times in total.

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Post #37by Eric Nelson » 28.07.2021, 23:50

So here's the thing: all this implies that our observations of stars and their radii and distances are very limited and there's so much more than we ever found.
Plus think of how hard it can be to measure a star's true size especially when it's so far away.
We base our best calculations from our best instruments regardless of date.

Remember Betelgeuse at times was once estimated to be 955 or even 1,021 x Sol's radius, though late 2020 observations from the Solar Mass Ejection Imager (SMEI) aboard the Corolis satellite put its radius measurement at 764 +116 -62 x Sol's radius (and a consequently closer distance of 547.9+ +90 - 49 ly or 168.1 +27.5 - 14.9 pc distance from Sol), and that's a massive improvement over the previous calculations.

VY Canis Majoris's 1,420 +/- 120 x Sol's radius from the VLT's 11.3 +/1 0.3 mas parallax measurements between 2011 and 2012 (which puts it near the modelled maximum for stars - the theoretical Hayashi limit - which's 1,500 x Sol's radius), and ​late 2013 measurements by Matsuura and others of the star estimated at a vague 2,069 x that of Sol's (beyond the Hayashi limit) makes it 1 of the well-known stars to exceed 1,000 x Sol's in radius. https://doi.org/10.1093%2Fmnras%2Fstt1906
Some of the stars we found are currently estimated to be larger, like HR 5171 Aa (at no more than 1,575 X Sol's radius though at least 1,060 x Sol's), WOH G 64 (at 1,540+ x Sol's radius), and Stephenson 2-18 (at approx 2,150 x Sol's radius) for example, though the radii values for stars like Betelgeuse and VY Canis Majoris for example are better-characterized, therefore VY Canis Majoris is technically the largest star we found that's well-characterized (at least 1,300 x Sol's, but most likely 1,420 x Sol's, though no way over 2,069 x Sol's).
https://www.aanda.org/articles/aa/full_html/2013/11/aa21683-13/aa21683-13.html
Plus it's a pulsating variable, meaning its maximum and minimum semi axes keep changing over periods (whether its for radial or non-radial pulsating stars).
Yet it's only 1,170 +80 -70 pc (3,816.03 +260 -230 ly) from Sol whereas Stephenson 2-18's currently said to be no closer to us than 5.8 kpc (18,917.07 ly) from Sol while the HR 5171 stars are anywhere between 4,900 (1.502347 kpc) and 11,700 ly (3.587236 kpc) from Sol, and WOH G 64's 49.877 kpc (162,677.02 ly) from Sol.
I know the URLs are 2012 and 2013 dated, but that's what's said about VY Canis Majoris to this very day.

There may be stars out there larger than VY Canis Majoris or some of the others we found (whether by reality or by estimates), but we have to look farther than we ever did before with very good technology.
And it would take highly advanced technology to accurately measure stars in other galaxies (as they're so much farther away from us than any star in our Milky Way).

Hopefully the JWST and its successors along with the telescopes of the 2040's give us very proper measurements of stars at such far distances.
We'll wait and see.


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