2024-04-30, 06:40 PM
(2024-04-30, 04:01 PM)theskyhound Wrote: Hello,Hello Greg,
rasvan, thanks for chiming in. But... let me suggest that one should not be making supplemental database objects for objects that are already in the database. This creates unnecessary overlap and confusion, and you give up the connection to all of the associated data in the SkyTools database for your star. Given that most every star down to magnitude 20 is already in the SkyTools database, it is pretty much a given that these stars are already there.
So, this is not a matter of adding objects but matching them. The problem is that with every major new survey, such as Gaia, new designations are created when they publish a catalog. Before Gaia it was IRAS, and before that Tycho-2 and before that it was HIPPARCOS. At some point astronomers are going to have to stop doing this, because we add yet another designation for a star that already has 10 of them, and they become more arcane over time. In the future I am going to fold Gaia data into the SkyTools database, and at that time I may add a cross reference as well. But that day is not today.
Antone- you are using Gaia-3 as your source, so it is natural to want to use those in SkyTools, but given that your stars must be relatively bright, or you wouldn't be able to do spectroscopy, I think the best thing to do is to use the existing designations that have been with us for decades or even longer. I suggest identifying the stars by the better-known designations and adding them to a list in SkyTools, but also adding the Gaia-3 designations as a note & headline so that it can be referred to when needed. This also has the advantage that now you will have all of the cross references available for each star, which makes it easy to look them up elsewhere to see what research has be done, and when you talk about your results with others, they will know what star you are talking about.
That said, there is no simple way to do this. There are two approaches you could use:
1. Find a way to cross reference your list of stars before entering them into SkyTools. Then when you do, SkyTools will recognize them.
2. Track down each star in SkyTools by its position via the atlas, and add that star to an observing list.
I should be able top help you with this. How many stars do you have, and what format is your list in? Feel free to post it here, or email it to me at support, and I will see if I can use one of my private tools to do the cross referencing and add the Gaia designations to a note for each.
Thank you for responding, but first, I also want to thank Rasvan for his suggestions. His approach is what I was considering, but there seemed to be no way to avoid one-at-a-time entry.
So now on to cross-matching. I have some expierence this past year attempting to cross match Gaia objects. I've writen my own Python/Astropy code for cross matching and I've used the CDS X-match service. In most cases, I was trying to match stars to a Gaia object rather than what I'm doing now which is matching Gaia objects to stars with more common designations. These searches have all been cone searches using RA and DEC to find the closest star. The results are generally not good. Specifiying a narrow cone usually comes up empty, and a wide cone may have too many matches. To make matters even more challenging, Gaia DR3 uses J2016.0 rather than J2000. This is a problem because I am interested in finding M-dwarf stars that may be very old halo stars. These have high tangential velocities so their positions can shift by more than 10 arcsec over 16 years. In fact, I am using tangential velocity to separate my M-dwarfs into disk and halo populations. This won't be perfect, but I think it is a reasonable way to start.
My next attempt will be to use the Gaia proper motions in RA and DEC to convert the J2016 cooridnates to J2000 by subtracting off the 16 year cumulative shifts. Then I can load this data into the CDS X-match service for a cone search. But which catalog(s) should I use to attempt the match? Which ones have identifiers that ST4 will recognize? Of course this assumes good matches, and I have not had much luck with that.
Anyway, this is where things stand now. After I post this, I'll go back to my Python coding to make adjustments to RA and DEC and then try another CDS X-Match.
I am open to suggestions.
You also asked about my file format and number of stars. My query to the Gaia data uses a number of qualifers that assure reliable and consistant position and photometry data. Then it uses color, magnitude, and temperature cuts to get M-dwarf stars. It limits absolute magnitiudes to stars bright enough for me to attempt spectroscopy and positional criteria for stars visible in the next few months. Once I have this list, I collect those with very low tangential velocity and those with very high tangential velocity. Each of these groups have 50 to 100 stars. I save these in CSV files that I can load into ST4 or into the CDS X-match service. (You also asked for a sample file, but, this forum will not allow a CSV attachment.)
Last year, I captured spectra for HD143739 and HD143740. These are are close pair of M-dwarfs in Draco. ST4 lists their magnitudes as 8.4 and 9.7 respectively. The calculated mag_abs using Gaia photometry gives 10.1 and 10.8 for these two stars. So this is what I am using as an approximate magnitude cutoff for target stars.
Antone