ID puzzle = A wrong chart in Terzan & Ounnas (1988A&AS...76..205T)

American Association of Variable Star Observers (AAVSO)
Fri, 01/27/2023 - 21:49

I have an identification puzzle for any of you who like this kind of research.

I am in the final stages of processing a list of 66,000 miras from the OGLE Team for VSX.
In this kind of work, it is pretty common to end up with lots of cross-identifications between the objects in the papers and stars already listed in VSX. But a number of those turn out to be wrong identifications in old catalogues and thus checking charts and catalogue data (colours, photometry, etc.) is required.

A large fraction of miras in this list (in the Sco/Oph/Sgr area) had been already discovered by A. Terzan et al. and published in a series of papers:


Some of the objects in the 1966 paper were included in the NSV catalogue by the GCVS Team.
Some of the objects in the subsequent papers were included in the NSV supplement.

The stars in the first paper have a different naming system.
SIMBAD adopts [T66b] NNN as the format identifier for the 271 stars in 1966JO.....49..258N.

The stars in the 1982, 1988 and 1991 papers have a running number from 1 to 3379.
The ID format is Terz V NNNN.
Some stars in the 1966 paper were included in the more recent papers and then have also Terz V identifiers.
So one should be careful not to append numbers 1 to 271 in 1966JO.....49..258N to the Terz V identifiers that started being used in 1982.

E.g.: [T66b] 57 is not Terz V 57.

All papers have finding charts. Hundreds of them.
Sometimes more than one variable is included in a single chart.
I already found a chart that was wrong. It is the one including Terz V 1648 and Terz V 1649. Their IDs are interchanged.

But now I found an interesting puzzle.
It involves two stars labelled as Terz V 1725 and Terz V 1728 in the finding charts published in 1988A&AS...76..205T.

The chart and the tables are inconsistent.

Terz V 1725 is cross-identified as [T66b] 57, which had got the designation NSV 9024 in the NSV catalogue (DR2, 2022).
Terz V 1728 is cross-identified as [T66b] 145, which had got the designation NSV 9031 in the NSV catalogue (DR2, 2022).

However, the two variables included in the chart have nothing to do with the actual positions of [T66b] 57 and [T66b] 145.

These two variables may be completely different and maybe they are already known, but up to now I haven't been able to identify them.

Let's review the information on the two original objects in order to clarify things a bit before starting the chase after Terz V 1725 and Terz V 1728.
Due to the ID problem, I will not use the Terz V identifiers for NSV 9024 and NSV 9031 anymore.


NSV 9024 comes with an additional problem.

[T66b] 57 is at 17 31 21.75 -30 06 00.5 (J2000.0) as computed per VizieR, based on 1988A&AS...76..205T.
SIMBAD gives the following coordinates, based on Gaia DR3: 17 31 21.80 -30 06 01.0 (J2000.0).
Finally the NSV DR2 catalogue gives the star position as 17 31 21.81 -30 06 01.0 (J2000.0).

However, they are all wrong.
The OGLE catalogue recently published shows there is a redder object which is a mira, 10" to the ENE of that brighter and bluer (although also a red giant) star.
We have Gaia DR3 data for both. The star at 17 31 21.80 -30 06 01.0 is Gaia DR3 4058632322491344384 and only varies from G= 14.33 to 14.60 (r= 16.19 - 16.48 in VPHAS+ DR2). While the mira is OGLE-BLG-LPV-240395 = Gaia DR3 4058632326899613696 and has observations ranging from G= 13.98 to 16.92 (r= 17.7 - 20.9 from ATLAS-REFCAT2 and VPHAS+ DR2). OGLE lists it as a mira with a period of 396.1 d., mean Ic= 14.83 and amplitude 2.79.

Charts in 1966JO.....49..258N have a much smaller resolution than the other charts so one has to be careful in assuming IDs in these extremely crowded fields.
Careful examination shows that -indeed- the lines pointing to the variable star position, place it slightly to the E of the brighter object.
One thing that happens with these Terzan charts is that they sometimes point to the variable star location but, if the star is faint, there isn't any dot drawn in the chart (!). Thus, if there is a close companion, you have to learn to ignore it and give more weight to the actual position the lines are pointing to.


NSV 9031 is the 325.6 d. mira OGLE-BLG-LPV-240441 = [T66b] 145, at 17 31 27.07 -30 06 29.4 (J2000.0).
The NSV identification is correct in this case.


So, now that NSV 9024 and NSV 9031 are correctly sorted out in VSX, in agreement with the charts in 1966JO.....49..258N and the current data from the OGLE mira paper and Gaia DR3, we need to find out what Terz V 1725 and Terz V 1728 actually are.
The chart is on page 243 on 1988A&AS...76..205T (links to the papers above).

Checking other Terzan charts of nearby variables to get familiar with their scale is a good starting point.
Searching SIMBAD using the Terz V identifiers to find the coordinates will work (assuming the only chart in error is this one!!).
And then comparing them with sky images to see if the star patterns are recognizable.
Using Aladin and the DECaPS colour images is currently the better choice. Red objects stand out easily and I have found that Terzan charts can be checked easily against these images.

We can't be sure if the actual variables shown in the chart will be close to the current positions or not. It doesn't seem to be the case, because sweeping DECaPS images around that area did not show any recognizable similar pattern.
If you want to give it a try and see if you can find where these two objects actually lie, you are welcomed to do so!
And maybe you have a different idea on how to recover them.

Good luck!