Create Observing List of Selected GAIA DR3 Objects

[aggregory]

I have a personal spectroscopy project I want to conduct using objects (stars) from GAIA DR3. I can create a CSV file with my selected stars that includes the GAIA source_id, ra, dec, and magnitude. Is there a simple way to create an observing list from a csv file. I know that I can import object designations and that ST4 will attempt to match them with the included catalogs, but that seems to be a one-at-a-time process and I don't think it is posible to match GAIA source_id's. And I don't need to match these stars with other catalogs. I can work with the GAIA source_id as the ST4 Primary ID in the list. Is my objective clear? Am I phrasing this question correctly?

Antone

[razvan]

Until Greg answers, my quick take:

You can import an observing list in exactly the format you mentioned. See the help page entitled "Create Observing List From File". According to it, "The objects in the file are matched to objects in the SkyTools database. There are no clear standards for designation formats, so this will sometimes fail. If an object is not recognized, you are given the opportunity to cross reference it to an object in the SkyTools database by hand or to create a supplemental database object for it."

You can do what is in bold text above.

Razvan

[theskyhound]

Hello,

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.

[aggregory]

Hello,

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.

Hello Greg,

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

[theskyhound]

I'm pretty good at star matching. Csv attachments have been enabled. Being the boss has its advantages. If you could pass on a list of your objects, I would be happy try importing them, but it would be best if they were more than just a sample.

[aggregory]

I'm not sure how many stars makes "more than just a sample". My original query produced 250,000 targets. (I suspect that is too many.) Since my interest is comparing disk M-dwarfs (low tangential velocity) with halo M-dwarfs (high tangential velocity) I trimmed off one group of stars from each end of the velocity distribution. For high velocity, I asked for those greater than 300 km/s. This list has 408 stars. For low velocity the limit was for stars less than 2 km/s and there are 523 stars. I attached a histogram of the velocity distribution for the orginal 250,000 stars so you can have some idea why I chose these limits.

I also created an HR diagram using the calculated absolute magnitude and color. There is clear difference in the magnitudes of the two groups for early M-dwarfs. Finally, I compared the photometrically calculated metallicity of the two groups in a second histogram and the halo stars seem to have less metal and are therefore older. The HR diagram and this histogram are attached.

I'm providing this background information simply because I think it is interesting and I want to see if I can detect differences in the two groups using low resolution spectroscopy. Perhaps I won't be able to, but it will be fun trying.

So, there are two CSV files attached. Both include all of the Gaia DR3 parameters I downloaded and the RA and DEC are in the Gaia J2016.0 epoch.

Thanks and Clear Skies,
Antone

[theskyhound]

Hello,

The stars in your list appear to be petty faint, and I'm surprised that you can do spectroscopy on such faint stars. Is your intent to measure radial velocities?

I should be able to look at this over the weekend.

[aggregory]

Yes you are correct, the vast majority of these stars are too faint, so yesterday I did another cut using the Gaia phot_mean_g_mag parameter. For the high velocity stars, there are eight that are between 11 and 13 magnitude. But I also have an 18-inch telescope that many have told me is unsuitable for spectroscopy, but it seems to work just fine. For the low velocity stars there are several dozen stars bright enough for my 8-inch telescope. I use a difraction grating for my low resolution spectroscopy, so I can go a bit deeper than it is possible with a slit spectrometer. 

Yesterday, I tried feeding my lists to the CDS X-match service. The WISE and 2MASS calatogs seemed to give the most matches. I also matched my lists against the GAIA DR3 catalog just to check that all the ID's and locations were valid and that there aren't some other problems with my lists. The GAIA DR3 matched perfectly, as it should since that is where the list originated. The eight stars from the high velocity list I tried to match individually. I first entered the GAIA source_id into the CDS Portal, then checked all of the alternative ID's given in SIMBAD. Then I tried those ID's in ST4. Some matched and some did not. I also tried entering coordinates to see if ST4 has a star within a few arcsecs. I'm still working on this.

Anyway, if you want to shorten the lists I sent, cut off the phot_mean_g_mag at about 12 or 13. In any case, for now it is the matching that is a challenge. I can work out specific targets later. I just need a more effective method for matching GAIA DR3 source_id's with other catologs and with ST4.

Thanks again,
Antone

[theskyhound]

Antone,

Have you looked for published cross reference data from the Gaia team? Usually catalogs include such cross references, especially for the brighter stars that you are likely interested in. With a cross reference from Gaia ID to a more tradition designation, such as HD or even Tycho-2, this would be much simplified.

[PMSchu]

Hi Antone,

Since the Gaia team is using epoch J2016 for their coordinates, could you set the date in SkyTools to that date, then look in the Interactive Atlas for stars at/near the published coordinates? This could reduce the effects of proper motion on the positions of the stars. Perhaps you've already tried this  .

I thought that you might ask SkyTools to do a 'Nearby Objects'  search around your M-dwarfs, but unfortunately that only appears to search for double stars not any type of star. The 'Nearby Objects' search is a feature of ST4 Visual, but isn't available in ST4 Imaging.

You have an interesting project.

Phil S.