<p>If you search by position in the <a href="http://simbad.u-strasbg.fr/simbad/" rel="nofollow noreferrer">CDS Simbad</a> database by position it will give you entries in all three of these catalogues. If you search by name, then it will look for matched objects in these three catalogues. I am unsure what the matching algorithm is - it must cross-correlation on the position and look for objects within an appropriate matching radius, taking account of the proper motion of the object and epochs of the various catalogues.</p>

<p>This will not be foolproof, but the density of 13th magnitude objects on the sky is low enough that false matches are highly unlikely.</p>

CC BY-SA 4.0
2018-08-08T07:47:28.160Z
Thanks! To double check that I understand; there are not necessarily pre-existing, hard-wired links between the objects in different catalogues. Matching is an algorithm that is applied at the time of the search. Have I got that right? (within the constraints of the question; roughly +13 magnitude, star-like objects)
uhoh
CC BY-SA 4.0
2018-08-08T08:14:26.343Z
@uhoh AFAIK this is done at the time of search. There are catalogues available where DR2 has been matched against other catalogues (e.g. see http://gaia.ari.uni-heidelberg.de/tap/tables ), but I don't think anybody has created one "supercatalogue" if that is what you are asking.
ProfRob
CC BY-SA 4.0
2018-08-08T09:04:42.627Z
*billions and billions* of hyperlinks ;-)
uhoh
CC BY-SA 4.0
2018-08-08T07:41:24.847Z
2018-08-08T07:41:24.847Z
ProfRob
<p>@MikeG's <a href="https://astronomy.stackexchange.com/a/27277/7982">speedy answer</a> to <em>"What star was the asteroid 2014 MU69 predicted to occult on 2018-08-04?"</em> lists three names for one 13th magnitude star, from three catalogues; 2MASS, UCAC4, and Gaia DR2.</p>

<p>My question could be slightly subjective, but I believe that someone familliar with the topic will be able to provide an authoritative answer.</p>

<p>For stars around 13th magnitude that do appear in all three, are they electronically linked between catalogs in some automated way, or do you pretty much check each of them, decide the objects are the same, and then make note of your conclusions if you are writing something up?</p>

<ul>
<li>2MASS All-Sky Catalog of Point Sources (Cutri+ 2003) </li>
<li>UCAC4 Catalogue (Zacharias+, 2012) </li>
<li>Gaia DR2 (Gaia Collaboration, 2018) </li>
</ul>

CC BY-SA 4.0
2018-08-08T07:34:18.297Z
Not clear what you mean. The three catalogues listed are separate catalogues. You can link them by cross-correlation  by position, taking into account any proper motion. Are you asking if someone has already done this?
ProfRob
CC BY-SA 4.0
2018-08-08T07:41:32.017Z
@RobJeffries I believe that is what I'm asking, but I don't know if "cross-correlation by position" has a deeper meaning than "check each of them, decide the objects are the same" or not.
uhoh
<star-catalogues>
For stars around 13th magnitude, are their entries in various catalogues usually linked, or does one do this manually?
uhoh
# For stars around 13th magnitude, are their entries in various catalogues usually linked, or does one do this manually?

(Asked by: username_0 on 2018-08-08)

@MikeG's [speedy answer](https://astronomy.stackexchange.com/a/27277/7982) to *"What star was the asteroid 2014 MU69 predicted to occult on 2018-08-04?"* lists three names for one 13th magnitude star, from three catalogues; 2MASS, UCAC4, and Gaia DR2.

My question could be slightly subjective, but I believe that someone familliar with the topic will be able to provide an authoritative answer.

For stars around 13th magnitude that do appear in all three, are they electronically linked between catalogs in some automated way, or do you pretty much check each of them, decide the objects are the same, and then make note of your conclusions if you are writing something up?

* 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)
* UCAC4 Catalogue (Zacharias+, 2012)
* Gaia DR2 (Gaia Collaboration, 2018)

**Tags:** star-catalogues

> **Comments:**
> **username_1**: Not clear what you mean. The three catalogues listed are separate catalogues. You can link them by cross-correlation  by position, taking into account any proper motion. Are you asking if someone has already done this?  
> **username_0**: @RobJeffries I believe that is what I'm asking, but I don't know if "cross-correlation by position" has a deeper meaning than "check each of them, decide the objects are the same" or not.  

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## 1 answers

### Answer by username_1 on 2018-08-08. Score: 3 | Accepted answer

If you search by position in the [CDS Simbad](http://simbad.u-strasbg.fr/simbad/) database by position it will give you entries in all three of these catalogues. If you search by name, then it will look for matched objects in these three catalogues. I am unsure what the matching algorithm is - it must cross-correlation on the position and look for objects within an appropriate matching radius, taking account of the proper motion of the object and epochs of the various catalogues.

This will not be foolproof, but the density of 13th magnitude objects on the sky is low enough that false matches are highly unlikely.

> **Comments:**
> **username_0**: Thanks! To double check that I understand; there are not necessarily pre-existing, hard-wired links between the objects in different catalogues. Matching is an algorithm that is applied at the time of the search. Have I got that right? (within the constraints of the question; roughly +13 magnitude, star-like objects)  
> **username_1**: @username_0 AFAIK this is done at the time of search. There are catalogues available where DR2 has been matched against other catalogues (e.g. see http://gaia.ari.uni-heidelberg.de/tap/tables ), but I don't think anybody has created one "supercatalogue" if that is what you are asking.  
> **username_0**: *billions and billions* of hyperlinks ;-)  

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