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Display GAIA EDR3 data from VizieR in GUIDE planetarium on the fly via a toolbar button

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#1 Guest_346229

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Posted 03 December 2020 - 10:00 AM

Are you sitting comfortably?  Then I’ll begin...

 

GAIA EDR3 has been released.  Below is how to fetch that data from VizieR on the fly with GUIDE planetarium software and display the stars, with a guess to colour from RP and BP (stars will be white if both of those don’t exist) and help on position, parallax and proper motions as well as including the GAIA DR2 ported over radial velocities (there are no new ones in EDR3).  Just about the rest of the data in EDR3 is cross identifications to other big surveys and technical data.  Note I’ve also not included error values, the general level of accuracy in GAIA is such that the vast majority of errors are negligible compared to what the vast majority of people need as long as you don’t go down to the faint ends of below 17th magnitude and even lower.  The faintest end of any survey is always suspect, but those objects are at the system’s absolute limit.

 

IMPORTANT :-  Guide downloads objects based on the area of the field at the LEVEL you are currently displaying.  If you use too big a level the sheer amount of data in EDR3 will lead to an immense file, a potential slowdown of either the internet during data retrieval or in GUIDE as it tries to plot them all, so be careful and rarely if ever go above a 1 degree field.  You’ll also be needlessly thrashing the VizieR servers, which is impolite.  I’ve set the TDF that it will only display at fields of one degree or less anyway.

 

Now, how to do it.

 

In your GUIDE directory you will find the following two files, download.txt and toolbar.dat.  There were slight changes to how the latter worked over time but I believe it remained backwardly compatible.  I run Guide 8 under Guide 9.0 software, as you could update Guide 8 with Guide 9 simply by copying the software over it, even though the data disks differed.

You load download.txt into a text editor.  To keep it simple we will replace a needless entry.  There should be one starting with the number 2799  for SDSS5 data, that is now out of date and much superseded, so it can harmlessly be replaced, it is doubtful anyone is using it.  With the editor change that line for this one :-

 

2799 -cI/350/gaiaedr3&-out=RA_ICRS,DE_ICRS,Plx,pmRA,pmDE,Gmag,BPmag,RPmag,RVDR2 g.dat

 

which is one line.  Check the column line up with other entries in the file.  Deactivated lines start with a # symbol, so those are offset by one column.  You need to ensure this one is activated so ensure the lined doesn’t start with a # symbol.

 

Now save the file back into the guide directory and ensure it has gone there and stayed as “download.txt” and not something daft like “download.txt.txt”, just pressing save instead of save_as should be fine, that’s it, that’s all that’s needed for that bit.  If there is no 2799 entry, pick another on the list starting with a # symbol that you don’t use, just remember the number at the beginning of the line as it will be needed again in toolbar.dat.

 

Now, how toolbar.dat works is documented here https://www.projectp...com/toolbar.htm but the basic principal is the number at the beginning of the line should match the number in download.txt.  So load toolbar.dat and search for 2799, when you at the line change it so it reads like this

 

   2799  !gaia3.bmp        GAIA EDR 3 data from Vizier

 

notice that there are three preceding spaces and it does NOT start with a #, which again would deactivate it.  All you’ll really be doing is changing the .bmp name and the English description.

 

If you had to use another number from download.txt search for that entry instead.  You can add lines but then you have to adjust an incremental number and you may also end up choosing a number that already exists so it is far, far easier to replace one that already exists in download.txt but isn’t needed.

 

You need a toolbar button image, so in the spirit of xmas come early, I’ll attach a simple .bmp file which must be saved into the GUIDE directory as “gaia3.bmp” and only that else it won’t be found.  There is no large button, you’ll have to make your own, and it simply says GAIA3 as there is no room to pixel edit in all the letters for GAIAEDR3.

 

Now for the tdf, cut and paste the following in a text editor and ensure it is saved in the Guide directory as “GAIAEDR3.tdf” and not GAIAEDR3.tdf.txt or any other daft variation winblows might try to force on you in default mode in later versions.

 

-----------copy and paste from next line--------------------
file g.dat
title GAIA EDR3 from VizieR
RA H  5 11
units0 -2
de d 22 11
mag  73  8
photo B:84,6 V:73,6
~b  2   1 GAIA EDR3\n
~r  5  10 \nRA  2000  %s   Dec2000  %[22,10]\n\n
~b 73   8 Gmag    %s\n
~b 84   8 BPmag  %s\n
~b 95   8 RPmag  %s\n
~b 40  11 \nPlx  %s  mas\n
~b 51  11 \npmRA  %s  mas/y\n
~b 62  11 pmDE  %s  mas/y\n
~b106   8 \nRadVel  %s  km/s\n
~r  2   1 \n^GAIA EDR3//xh ttp://vizier.u-strasbg.fr/viz-bin/VizieR-5?&-source=I/350/gaiaedr3&-c=%[5,9]%%20%[22,9]&&-c.eq=J2000.0&-oc.form=deg&-c.r=0.05&-c.u=arcmin&-c.geom=r&-sort=_r&!-4c=Find%%20Data^\n

 

epoch 2000
type 6
field 0.00 1.00
mag lim -29
shown 7
end
--------------------------------------copy and past only to the line previous------------------

 

Please note that the line beginning ~r  2   1 and ending in \n is all on just one line, in case of wordwrap, and is followed by a blank line which itself is followed by the line epoch 2000, so correct that if needs be.  Also I had to add a space in http (so it reads h ttp instead of http) to stop the editor forcing it to be a compressed actual link instead of text, so that superfluous space will also need to be deleted after you've pasted into a text editor.

 

Launch Guide.  Find a field of interest and zoom into a 1 degree or less field size.

 

Your toolbar button should have appear for use, if you can't read the details on it hovering overthem should popup a tooltip with their descriptions from toolbar.dat.

 

Click on the GAIA3 one (ensuring you’re connected to the internet of course...).  It should go fetch the data from the internet, if vizier is up.  A file called g.dat will be generated in Guide if it works, and if that is there have a look at it in a text editor to ensure it is not an empty file, that there is tabular data in it.  If it isn’t there check your download.txt and toolbar.dat.  Also, whether or not it downloads from VizieR may very well depend on your system and how GUIDE uses inbuilt aspects of winblows to retrieve the data from the internet, and also as versions of winblows progress you can end up stymied by permissions and firewalls that weren’t an issue in earlier incarnations, so if the download and toolbar files are correct and it hasn’t worked it may be due to your specific setup, and I’m not a computer guru so I won’t be any help.  If you get a file in the GUIDE directory called g.dat then something went to the internet, as long as it is not 0 bytes big (of course you have to make sure you are in a field with stars in them before you download)!

 

Goto ‘Toggle User Datasets’ via the menu, it’s under EXTRAS.  Scroll down to the GAIA EDR3 from VizieR entry (alphabetical listing) and double click on in it and then turn it on, even if it already is asterixed to say it is on.  Some tdf files work automatically in Guide, some don’t.  In this instance when you first use it there is no g.dat until you have pressed a toobar button, so it may be on but not aware there is any data until you double click it on again.  Or try just relaunching after downloading the data as that sometimes fixes it.  There has to be stuff to find for it to find it...

 

You will get stars of attempted colour (sometimes overlying almost exactly stars already plotted in Guide, so you might have to press NEXT in on right click to get at the EDR3 info).  Right clicking and clicking on More Info gives magnitudes, parallax, proper motions (I’ve not included “total proper motion”, there are limitations on line length in download.txt and anyway it’s useless without Position Angle) and DR2 radial velocity if any.  If RP and BP exist Guide will guess a colour to plot the star as, it’s a guess but not exact, pale yellow might actually be yellow, and sometimes you’ll get an orange hue for a yellow or red hue for an orange, due to the borders of the numbers as that GUIDE feature was originally set up for the B-V system, not BP-RP, but it works to some extent.  If there is no RP and/or BP magnitudes the star is plotted white.  If nothing is plotted there is no Gmag.  The data are there and right click on the position would show then, but the star isn’t displayed as there is no Gmag to plot to.

 

The stars are plotted to Equinox J2000 BUT to the 2016.0 epoch of EDR3, and not to the epoch of J2000, so they may not exactly match any field star from any another source that is plotted to Epoch and Equinox J2000 in GUIDE.  If you don’t understand that, don’t worry, just realise that if a star has high enough proper motion when it is plotted in GUIDE it will have moved on from the GUIDE position due to that proper motion.

 

More info includes a link at the bottom which will open a browser window with the full GAIA EDR3 details for that star from VizieR.  Actually you might get more than one star at times as the search has an arbitrary 3 arcseconds radius.

 

Finally, every time you do this the file g.dat in the guide directory gets more data added to it.  You can simply delete this file to start from fresh.  Or alternatively, though a little tedious, if there are fields you want to keep then you have to look for their RA and Dec in degrees and delete all the entries with different coordinates.  A new g.dat, or further g.dat appendments, will occur next time you push the toolbar button.

 

Is a double star is of reasonably high common proper motion or optical, you may ask?  Well, if you have Guide and the internet you can ask EDR3 what the parallax and proper motions are and make your own mind up, or if you want to check the brightness and colours via it (remember, Gmag is a red colour, so near visual when the star is white but progressively brighter than visual the redder the star is, and BP and RP are a blue and a red, not Blue and Red).

 

This was far quicker to actually do, test and setup as a feature for GUIDE that it was to write this up!  I’ve played with it a couple of times, it works, at least on my machine.

And they all lived happily ever after, exclusions apply, warranty limited to 0 years.

 

[attachment=1656861:gaia3.bmp]


Edited by wdstdf, 03 December 2020 - 10:04 AM.

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#2 sg6

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Posted 03 December 2020 - 10:06 AM

Tell Gerry to get his finger out and make it easy.

Professor Gilmore if you want his full title.



#3 Guest_346229

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Posted 03 December 2020 - 10:24 AM

Tell Gerry to get his finger out and make it easy.

Professor Gilmore if you want his full title.

It is easy if you just use VizieR, the above is only for folk who like to plot there stuff in their planetarium software.  There are also cone search features at several sites listed as 'partners' by the gaia website.

 

ESASKY, whatever that is, will also give plots of it apparently in an online interface, I think it's rather like the online google telescope or things that plot up dss images.  Aladin will no doubt have it integrated already if it is in VizieR.

 

TopCat is really good at getting at things like this but has a learning curve, and needs java.

 

You'll find most of the apps and software around, like astrometrica and skyplotting software and other things, actually source their data via the VizieR pages in the background for large datasets.

 

Most of the EDR3 is wasted on thoroughly pointless XID entries, even thoroughly pointless for astrophysicists, you should always do your own cross ID so you now its quality.

 

The above is also for if you want stuff locally on your computer, ready for if you are going somewhere without 'net access.

 

If you ask a professional they'll either give you a link to a python script on github, or tell you of some ADQL server, or worst of all tell you of a jupyter notebook that does everything they think is useful but nothing an observer needs, probably some model to do exoplanet stuff or stellar evolution stuff or something.  We're lucky they still use RA and Dec instead of this heapix thing taking over.


Edited by wdstdf, 03 December 2020 - 11:00 AM.


#4 Guest_346229

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Posted 03 December 2020 - 11:10 AM

Fair enough, because I've done a step by step thing to cover it as simply as possible it's got very longwinded and more which makes it look complicated, but it is in fact simple.  Here's a concise version :-

 

Guide users, in your Guide directory replace the line starting 2799 in download.txt with this one

 

2799 -cI/350/gaiaedr3&-out=RA_ICRS,DE_ICRS,Plx,pmRA,pmDE,Gmag,BPmag,RPmag,RVDR2 g.dat

 

replace the line with 2799 in it in toolbar.dat with this one

 

   2799  !gaia3.bmp        GAIA EDR 3 data from Vizier

 

Extract the two files from the attachment into your guide directory (the forum won't let me attach a .tdf file), virus checking first if you wish via jotti.org

 

Ensure you're connected to the internet and test the toolbar button.  If it doesn't work, relaunch Guide a coupla times and toggle the dataset on via menu, if it still doesn't work it's probably specific to your setup.

 

[attachment=1656926:gaiaedr3.zip]



#5 fred1871

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Posted 03 December 2020 - 07:16 PM

I think the most useful comment thus far on GAIA EDR3 is by WRAK (#27) in the thread Gaia - the demise of amateur double star measures?

Quote: My post was premature like a grade 5 orbit. Data model for DR3 is still an announcement not met by EDR3, sorry



#6 Guest_346229

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Posted 03 December 2020 - 08:45 PM

Well what wrak said will still be somewhat true even after final release.

 

I've been predicting for ages that some variables and binaries from gaia will be as spurious as a lot of the Hipparcos ones were, and probably just as unconfirmable.

 

I wonder if anyone will revisit all the HDS unconfirmed doubles using GAIA?  It will be the first time anyone has had a chance to with better data in bulk terms.  Granted some are confirmed, The 6th orbital catalogue has a bucketload of them included nowadays, though I've never checked the grades of those orbits some will have short enough orbits of only a few years but likely not many observations and probably often interferometric ones.  The defining of all these new 'streams' from parallaxes that are going to be < to << 0.1 mas in GAIA is a bit of an eyebrow raiser too.  I noticed one youtube video they released said "improved precision" in its narration, without any mention of improved accuracy.

 

I always used to pronounce HDS double as hideous and TDS ones as tedious by running the pronunciation of the capitals together.  Can't play them games if they use GDS at all.  It's available in WDS.  If any do eventually appear they are more likely to end up in WDSS, if not already there seeing one professional paper found 850,000+ cpm pairs in DR2 and they were imported I believe.

 

I've just set up a count in TAP VizieR to see how many negative parallaxes there are in EDR3 (there were a lot in DR2), it'll probably time out before it finishes or take days though.

 

GAIA dr2 has been very useful in providing lots and lots of doubles with measures for epoch 2015.5 though, and that in itself will likely not be improved upon by later releases as the epoch won't change that much.  I think the last allsky big batch of measures included in WDS was from 2MASS, done by the WDS team themselves.

 

On the other hand, EDR3 does hint that STF 391 might be a valid pair given the new parallax and pm values, whereas DR2 didn't, but on the other other hand final dr might say something else all over again.

 

You don't really get the hang of a dataset until you've played with it a long time, irrespective of the claims upon it or the models used for it, you get a feel for inconsistencies if you use it a lot for any projects or research.



#7 c2m2t

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Posted 03 December 2020 - 10:02 PM

Hi wdstdf!

On a subject totally unrelated to the topic (I apologize) but pertinent to information within your post and that is:  

 

I have been trying to contact the developers of Guide to acquire a copy of the software and the most recent update that I have been able to track of their website is from 2016. Are you or anyone reading this topic able to direct me to the developers? That would be greatly appreciated!!

 

Cheers, Chris.



#8 Guest_346229

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Posted 04 December 2020 - 09:28 AM

c2m2t

 

Hiya

 

I had a quick look at the website and this was there :-

 

https://www.projectp...com/update9.htm

 

that looks to be the last one, May just gone.  There's still a mailing list you can look at the public archives for but Guide is barely supported nowadays, with some basic support, he made it public domain under GPL some time back.  That may even mean it's okay to copy the DVDs if you know anyone who has one and haven't got 9.1.  I'm still on updated to 9 software from 8's CDs because of a lot of tweakings I've done over the years that I don't want to lose.  If you have 8 go to the bottom of this link as it is a different update compared to updating 9, after all there is far more data on DVD than on a couple of CDs.

 

Also notice that as there aren't that many updates nowadays (apparently it is barely ordered nowadays, most folk who want it have it, and he still has to make a living writing code so Guide doesn't get much time, although the website suggests you can still purchase the DVDs) he has been known to forget to not only update the date on the update page screen but on occassions has also forgotten to update the date when you check the version number with HELP->ABOUT !

 

 

 

It is strange how we all get loyal to our favourite package.  I noticed when looking into the news about Wilman-Bells close down that they still sold MegaStar and to my knowledge that hasn't been updated in years, because really unless there's new data or bug fixes the ability to generate stuff for observers stays much the same, just people have different preferences and different packages have different little bits.  I've tried some of the current new ones, the fully public domain ones and the ones with a 'lite' version and despite clever things like simulation real views with stars looking like stars through a telescope etc I find there functionality poor.  However, that might just be because I am used to something else.  I think it was the sky, way toooo expensive, megastar and guide when I first looked all that time ago, and I chose guide.  They all had an added expense because I'd also to purchase a CD drive and they were about ten times more expensive than they are now (and that's not including adjustment for inflation and money depreciation).  Boxes were harder to put new hardware into too then, solid heavy steel things with next to no room in them and I always grazed or cut myself whenever I did an upgrade!



#9 c2m2t

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Posted 04 December 2020 - 11:37 AM

Hi Wdstdf!

 

Many thanks for that link. I have ordered a copy of V9.1. A number of years back I purchased a new controller and motor package, an FS2 unit from Michael Koch in Germany, for my AP 600E gem. I have been looking for solutions/software that would allow this mount to be controlled with a computer. Guide is one of the 2 softwares that are named as recommended software, the other is SKY. A small number of FS2 users have indicated that they have been able to control their mounts using Sky Safari, but I have had no such luck. Sky Safari does a wonderful job on my other mounts and has a great inventory of double stars. The FS2 unit is a bit cumbersome when scrolling through the ra/dec mode...you can't enter data, you can only scroll to it...hence the hope to get more control with the Guide software. I look forward to its arrival in the mail!

 

Cheers, Chris. 



#10 Inkswitch

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Posted 04 December 2020 - 12:50 PM

Hi wdstdf!

On a subject totally unrelated to the topic (I apologize) but pertinent to information within your post and that is:  

 

I have been trying to contact the developers of Guide to acquire a copy of the software and the most recent update that I have been able to track of their website is from 2016. Are you or anyone reading this topic able to direct me to the developers? That would be greatly appreciated!!

 

Cheers, Chris.

Hi Chris,

 

Presumably you have tried email, in case you haven't the address is pluto@projectpluto.com.  I recently purchased Guide 9.1 and had an issue with the disk they sent me.  I emailed them and got a prompt response with the result that the issue has been rectified.


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#11 Guest_346229

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Posted 04 December 2020 - 01:14 PM

Hi Chris,

 

Presumably you have tried email, in case you haven't the address is pluto@projectpluto.com.  I recently purchased Guide 9.1 and had an issue with the disk they sent me.  I emailed them and got a prompt response with the result that the issue has been rectified.

Interesting point, I did once get a late email response from projectpluto telling me my mail was found in a spam folder and not recognised at first, I was using a new one at that time.  The spam folder apparently didn't get looked at regularly and probably if like the rest of us only gets a quick cursory glance at every now and again any legitimate emails might get missed.  I think their email provider probably didn't like my obscure sounding email provider for some reason, so that could have happened especially if you're c2m2t@obscurename.org or similar.  That doesn't mean they haven't got a sensible set up at projectpluto, I know from experience that from time to time quite legitimate emails from legitimate addresses have ended up in my spam folder even though ALL junk and spam rules are deactivated on my account!  Evidently my email provider doesn't trust .edu addresses because I haven't made any rules against them.  It let's real spam through at times though...

 

Maybe always make sure you've got a clear capitals subject heading that most certainly doesn't sound like a spam engine generated one.  We used to get "Important - please read!" headed emails from the CEO once upon a time... ...which was doubly ironic when a spoof email managed to slip in from his address once straight through the security!


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#12 fred1871

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Posted 05 December 2020 - 12:22 AM

Quote:  I've been predicting for ages that some variables and binaries from gaia will be as spurious as a lot of the Hipparcos ones were, and probably just as unconfirmable.

 

I wonder if anyone will revisit all the HDS unconfirmed doubles using GAIA?  It will be the first time anyone has had a chance to with better data in bulk terms.  Granted some are confirmed,

 

The big problem is not with HIP (Hipparcos) doubles but Tycho doubles. The HDS doubles are mostly being found to be genuine pairs; a few turned out to have likely short orbital periods, so already have preliminary orbits, sometimes fairly good ones. Usually (unsurprisingly) within reach of the 4-metre scopes using speckle cameras.

 

Tycho is a different story. Different forms of data analysis, and two bites at the job. The original Tycho doubles list (not huge) was extended with a new analysis using different methods and algorithms. The result was a much bigger list, from memory 14,000 or so, most of which when checked have proved to be non-existent in he form described -"bogus" doubles as WRAK calls them, mostly single stars. Professionals who check on them get a high rate of single stars, and as the big scopes can go much closer than Tycho, that will (except for a likely small number that have closed up since ~1991) be the story. The eventual figure seems likely to be 80%-plus bogus. 

 

Even a lot of those listed as 2 arcseconds or more apart by Tycho are bogus. There will not be a high percentage of those at say 0.5" to 1.0" that could "disappear" below 0.04" within a decade or two, so they're beyond 3.5-metre scopes.  Rapid change at that level requires certain astrophysical parameters to be possible, starting with a near-periastron section of orbit. When the details are put together the coincidence of timing becomes infrequently possible. With the wider examples, no real likelihood.

 

So, it's better to not mention Hipparcos doubles as an example of large-scale problematic "discoveries". Tycho doubles are a problem. There are enough to require some attention, not simply ignoring. By the way, WRAK, Wilfried Knapp, published in the JDSO a while ago a long list from computer searching to try separate sheep from goats of the Tycho doubles using Gaia DR2 data. Did Gaia record two stars or one? A very good first sifting to deal with the Tycho problem.


Edited by fred1871, 05 December 2020 - 07:17 PM.

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#13 Guest_346229

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Posted 09 December 2020 - 08:37 PM

 

Did Gaia record two stars or one? A very good first sifting to deal with the Tycho problem

 

I didn't know that he'd done that, I missed that one, although I have had a tendency in the past to dismiss anything to do with Tycho doubles since I first checked into them many years ago, it is only very recently many could be assessed short of a major observing survey with professional level kit.

 

I read some of the EDR 3 blurb over the weekend and have been playing with TDSC since then.  By the way, the astrometry and photometry in EDR3 is it, no use waiting for DR3, it will be the same, so it is stated.  Likely no difference till 4, which could well be half a decade ago.

 

I'm been playing with the tdsc stuff to get some idea of the changes/updates in values in EDR3.  For many close pairs parallaxes now match better.  Since CDS xmatch came out checking against large datasets has become far simpler so I bled the HDS and TDS and TDT ones out of VizieR WDS and kept those with single observations (ie unconfirmed) and separations quoted as 0.6 to 5 arcsecs then xmatched them against EDR3 via CDS xmatch to five arcseconds.  That way you get any pair in GAIA EDR3 that is separated by that or less.  I haven't exactly found a quick and easy way to ditch all the single hits without doing it manually for fear of baby and bathwater scenarios (false negatives are a pain) although ironically I've found out how to do the pairs.  A couple of simple filterings, based on guesstimates (even though passbands between GAIA G mag and BT and VT are different you can cut out all the really faint stuff from GAIA lying within 5 arcsecs of a star easy enough.  BP isn't available for every secondary, sides which the passband ain't anywhere near BT's).  One or two of the hightest proper motion ones might get missed, although I haven't looked into that yet.

 

There's about 11,000+ hits but many of those were lost on filtering down to pairs, still several thousand left.  I decided to check them manually using the TDF and Guide, but far too many, so I did parallax filtering with pairs matched in said and proper motion lower cutoff too.  A set of 'real' objects, so to speak, well, fair confidence cpms.

 

All of the resulting pairs were split with GAIA, down to 0.57 arcsecs in one case, with all pa and sep and delta mag sufficiently close to the Tycho figures, I've confirmed about two dozen so far.  Very few if none of those were split by DR2.

 

EDR3 is a LOT better so far.  If only it had the radial velocity stuff I'd replace by copy of 2 with it, but I'm still doing comparisons.  Besides which it takes ages to download and tweak for use locally format wise, which might take the best part of 2021.  I've also downloaded the 7 million with dr2 radial velocities and formatted it for Guide using the ARI TAP service which was quick, managed to get that down to half a gigabyte for Guide use.

 

It's growing on me.  The unsplit Tycho Double Stars are however not proven single, at least to a certain separation, probably subarcsecond, not sure yet.  Of course with a quarter century epoch gap twixt tycho and edr3 even then you couldn't be sure an orbit hadn't closed it up.  Meanwhile, when first tested before the filtering I found some Tycho Doubles of 2 arcsec or so couldn't be confirmed.  But then you don't know if that is a GAIA issue, even for similar magnitude pairs which can readily be split down to just below 0.6 arcsec.

 

There's some fun there if you like messing with data.  WRAK will probably eventually do a paper or two, he's good at bulk data processing.

 

Incidentally, for double confirmation there are very modern optical and near infrared surveys where you can download small fits cutouts of these stars and use something like aladin to see they are double.  Many are about 1 arcsec resolution, ish, and if not too bright figure 8's can usually be cleanly distinguished, although not always safely measurably so in terms of separation as at times you have to mess with the pixel histogram so much you aren't going to find photocentres to measure from readily.  Or, I don't know how you'd do that.  Or both.


Edited by wdstdf, 09 December 2020 - 08:38 PM.


#14 fred1871

fred1871

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Posted 09 December 2020 - 09:10 PM

I'll repeat a simple point (or two, in different words). The vast majority of Tycho doubles that have listed separations wider than 1 acsecond could not have closed beyond reach of large scopes during the epoch difference from Tycho to Gaia. A small subset could. In the case of checks before Gaia, the possibility diminishes.

 

At one time I evaluated Tycho doubles images from the 2MASS survey. A high proportion of the pairs I looked at, all supposedly 1.5" apart or wider, *were single on the 2MASS images which were made in the late 1990s, so there was little epoch difference. Known doubles of similar magnitude and separation, measured a number of times over the years, in every case showed clear elongated or doubled images of the expected separation and angle.

 

It would be too tedious to go through in this way the many Tycho pairs that were in this wider category. And there was no good reason to think closer pairs would do better. Some of those closer pairs had been found single already by professionals with large scopes.

 

Conclusion was that the analytic treatment and algorithms used were far too capable of producing false positives.

 

*spelling it out - the 2MASS plates were nearly always good for indicating elongated images down to 1.5" separation - established from genuine doubles. The generally dimmer magnitudes of Tycho doubles reduced image spread, helped by 2MASS not being nearly as deep as the general surveys that go to 20th mag or so. A few pairs to 1.3" showed elongated on 2MASS.

 

I've not yet spent enough time with the Gaia EDR3 to comment on it yet.


Edited by fred1871, 10 December 2020 - 08:19 AM.



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