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UXORs vs ISA etc.

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MJB's picture
UXORs vs ISA etc.

VSX lists some stars as UXORs and others as ISAs, each description refering to the other implying they are the same thing.  I think the UXOR description references the ISA as the lable used in the GCVS.  Are they in fact identical classifications and if so why are two different terms used in the VSX?  I think the same thing is going on with the T Tauri stars.  

Sebastian Otero
Sebastian Otero's picture
UXORs and I-types

Hi Bruce, nice question.

If you read the VSX Variability type definitions, you will find that the UXOR class is better defined and that is what we currently use in VSX.
Here it is:

UX Orionis stars, which are collectively known in the literature as UXors. Subgroup of Young Stellar Objects that show irregular variations with a wide range of amplitudes from barely detectable to more than 4 mag in V. Most of them are Herbig Ae/Be stars but there are some T Tauri stars with later spectral types also showing the same behaviour. Large-amplitude variability is confined to stars with spectral types later than B8. There are two principal components: (1) irregular variations on time-scales of days around a mean brightness level that changes on a much longer time-scale (typically years), sometimes in a quasi-cyclic fashion, and (2) occasional episodes of deep minima, occurring at irregular intervals but more frequently near the low points of the brightness cycles. UXors show increased polarization when the optical light of the star becomes fainter (presence of clumps in our line of sight) and redder, while in extreme visual minima there is a color reversal. Currently mixed among the ISA, INA or INSA classes in the GCVS.

So there are UXORs hiding among other GCVS types, not only ISA.
But are all ISA-type stars UXORs? We can't be sure so we are classifying it as UXORs in an individual basis when they show photometric evidence supporting that.
We are not checking all light curves or spectral/color information (that would reveal the UXOR nature) one by one so it sound like a good project for someone who wants to help submitting VSX revisions to confirm these objects when appropriate.
The stars that still carry the I-type classification from the GCVS (in any of its variants) may be considered as objects needing further study or confirmation.

And yes, we are doing the same with the T Tauri stars, classifying them as WTTS or CTTS when that distinction is possible or TTS when not, instead of the IT/INT types in the GCVS.


pox's picture
There's a bit of confusion

There's a bit of confusion here, due largely to the old GCVS classification system, which is going to be with us for a while yet! But there most certainly isn't a 1-to-1 mapping between ISA and UXORs. So while several UXORs are ISA's, not all ISAs are UXORs! Hope that's clear...

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