Show UCAC4 stars in the Deep Sky Annotation

[admin]

Hi folks,

out of interest, when showing these additional stars, how much value is in having the magnitude visible and how much in the stars ID?

I have been looking at the possibility of storing magnitude data inside the SharpCap plate solve index - because of the way the index is stored, I can store the magnitude of each star to (say) an accuracy of 0.05 mag for very little additional storage cost - about 0.5% increase in the size of the index. Unfortunately there is no such clever way to store an ID without increasing the size of the index by maybe a factor of 2.

Having magnitude data available would mean that SharpCap could display positions and magnitudes of about 10 million stars in deep sky annotation - would this be useful from the point of view of having known magnitude stars labelled?

cheers,

Robin

[Jean-Francois]

Hello Robin,

The star magnitude depends on a lot of parameters.
The spectral band, the catalogue and the time if the star is variable.

For scientific work, the people search the information in the CDS database (with Simbad, Aladin or Vizier).
For a quick view of the stars magnitude (note I guess that an accuracy of 0.1 mag would be sufficient), the star magnitude would be an interesting information.

You mention that you have about 10 million stars in the Deep Sky Annotation tool.
That is a lot and it means that a lot of stars are in different catalogues: Tycho, UCAC4, USNO, GAIA. So which ID will you use ?
Try this for the HD123456 star : https://simbad.cds.unistra.fr/simbad/si ... BAD+search

Do you try my script for the view of the UCAC4 stars ?
You will see that the binary search of the stars in the 4GB UCAC4 data is very quick (thanks the compiled C-code).
I was thinking to add the HD star catalogue (but the coordinates are still a mystery) or to add the GAIA stars.
So my goal is to upgrade my script with 2 additional catalogues (HD and GAIA).

What about the position ? ... which accuracy ? Ideally rounded at 1 arcsec, top would be 0.1 arcsec.

Regards,
Jean-Francois

[admin]

Hi Jean-Francois,

this is all based on the data used for the SharpSolve plate solving index. The default index contains about 10 million stars distributed over about 400 tiles covering the sky. There is some overlap, so there are probably only 7 or 8 million distinct stars. Positional accuracy is approximately 1 arc second and the file is packed at roughly 4 bytes per star to store the positional information. The data is sourced from GAIA DR3 with the addition of the few hundred bright stars that are missing from Gaia. The data does not go to a uniform magnitude depth, since it is designed to have a roughly uniform star density across the sky, rather than include all stars above magnitude X.

I don't store any star ID information and I'm not intending to add it, since it would require a minimum of 4 bytes per star, doubling the file size. That's too much cost for the amount of utility this would have, remembering that the primary use of that data is plate solving. However, because I store the stars in each tile in descending order of (visual) magnitude, I can add magnitude data at a storage cost of approx 0.02 bytes per star on average.

I will have to have a look at your UCAC4 scripts - I haven't so far. As a result of playing around with the extra few million stars from my plate solving index, I have made some performance optimizations to annoation this week, including not recalculating the list of objects in (or close to) view unless the mount co-ordinates move of catalog data or selections are changed.

cheers,

Robin

[Jean-Francois]

Hello Robin,

The view of the "Plate Solve Index Stars" works good.

It is interesting to see the magnitude difference (up to around 0.3 mag) with the UCAC4 stars.

But, the behaviour of the "Clear" button is changed now.
In the past, the objects from the Pasted from Clipboard were disappearing after a click on the Clear button.

Now, the objects annotation stay visible until the box is unchecked or a different catalogue is selected.

Regards,
Jean-Francois

[admin]

Hi Jean-Francois,

Ah, the failure of the clear button is because I forgot to make it clear the new cache of 'near view' items. I will fix that (one line).

I tried to estimate V magnitudes for stars for the plate solve index from G and Bp-Rp according to the relationships given here - https://gea.esac.esa.int/archive/docume ... tml#Ch5.T8 . In some cases in Gaia the Bp-Rp is not available, so the G magnitude gets used unaltered. For the plate solving side of things all I need is that the stars are fairly well sorted in order of decreasing brightness, so the approximation is good enough, but the sigma shown is 0.046, so it's not surprising that there are differences of several sigma in places.

cheers,

Robin

[Jean-Francois]

Hello Robin,

For general use, the actual magnitudes are OK.
Thank for fixing the "clear" button.

Regards,
Jean-Francois

[Jean-Francois]

Hello Robin,

The "Clear" button works, but one star or target stays all the time visible.

That is the last "selected" target from the "Objects In View" ... visible in yellow on the image.

Regards,
Jean-Francois

[admin]

Hi Jean-Francois,

I think I can see why that might happen - will have a look at fixing it for the next update.

thanks,

Robin

[astrocalina]

Hello,
I've tried the script (version 1.4) but I will receive as answer "No star found below the magnitude limit". I'm quite sure that a lot of stars are below magnitude 16 (I've checked with ASTAP too and for sure I've have stars with magnitude 10 or 11), and I set the limit from 8 to 16.
I'm sure that I made some mistake somewhere but I don't know where.

Thank you

[Jean-Francois]

Hello astrocalina,

Do you install the script from this ZIP file ? viewtopic.php?p=43503#p43503
It should be the version 1.6.

Modification: for the last version, please download the file from here: viewtopic.php?t=8255
Ignore the attachments of this message !

Regards,
Jean-Francois