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Irregular To Semi-Regular "Variable Type" Changes

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rglassner
Irregular To Semi-Regular "Variable Type" Changes

 

I have recently started observing variable stars and have mostly used the AAVSO Binocular Program to find bright variables suitable for my situation.  I have compared information about these long period variables from several sources that include the AAVSO Binocular Program list, VSX, my AAVSO Star Atlas (Rev. 2, 1990), and my Norton Star Atlas (17th Edition, 1978).  Five of the thirteen stars that I have observed (miu cep, bu gem, xy lyr, bl ori, and vy uma) have had "Variable Type" changes from the earlier AAVSO Star Atlas or Norton Star Atlas when compared to the current AAVSO Binocular Program list and/or VSX.  All five of these stars were listed as either "L" type, "Irregular", or "Type Unknown" in the two earlier books.  The binocular program list and/or VSX show them as either SRB or SRC. 

I would like to better understand how these changes were made.  The questions that seem appropriate to better understand this change process include:

1)  What standard or acceptance criteria was used to decide that there was a need to recommend a "Variable Type" change?

2)  What organization determined that the recommended changes were appropriate?

3)  Did this organization receive input from other organizations in determining that there were recommended changes to be made? 

4)  Once the change was recommended, what organizations were involved in the process to approve the recommended changes? 

5)  Is the process including the acceptance criteria that was used to make these changes described on a website or in some document? 

6)  Were all of the organizations that were involved in the change process also approvers of the standard/document that described the change process that was used?

Can anyone shed some light on the process that was used in making these "Variable Type" changes? 

I was surprised to see that a number of long period variables that I have observed have had Variable Type changes in recent years.  I am assuming that these changes are based on the availability of more information (e.g. observations) and not as a result of stellar evolution.

Thanks,

Rich

 

 

 

 

 

    

LKR
LKR's picture
This sounds like a job for Sebastian!

 Sebastian (the VSX guru) or one of his associates would be the one to answer this.

 

KL
 

Sebastian Otero
Sebastian Otero's picture
Classification changes

Hello Rich,

You already mentioned yourself the main answer to your questions: "I am assuming that these changes are based on the availability of more information (e.g. observations) and not as a result of stellar evolution."

Starting from that, I will try to answer all of your questions:

1)  What standard or acceptance criteria was used to decide that there was a need to recommend a "Variable Type" change?

Some of the points addressed here will probably be the answers to some of your other questions.

Each variability type has a definition based on several parameters, mainly: light curve shape, amplitude of the variations, period range, evolutionary stage of the object (position in the H-R diagram, color, spectral type, absolute magnitude). So, in principle, with enough information, it is not so difficult to classify a star into one of the known variability types.
You can take a look at the variability types document in VSX to learn more about each of them.

There will always be tough cases, for instance when the object has a weird nature or when the information available is not enough to classify it properly. E.g.: a very symmetric RRC-type star that can be confused with an EW-type binary if the light curve is not of a good quality (and even if it is...) and if we don't have color information or spectroscopic observations.
But nowadays we have more and more resources available (e.g. sky surveys) so classifying variables is becoming easier.
However, the number of variable stars discovered by surveys is large and they usually classify their stars automatically without human intervention, and that may end up with wrong classifications. So one tip: don't blindly trust the published information.
In VSX we try to correct what is wrong and be as up-to-date as possible but we also trust in the VSO community to help us with that task. This also answers some of your other questions:

2)  What organization determined that the recommended changes were appropriate?

That is one of the purposes of VSX. We receive new variable stars discoveries and also revisions to already known variables. Those revisions may include changes in the published variability type. We have the criteria (mentioned above) to distinguish among the different variability types so the submitters attach supporting evidence for the changes they are proposing and we confirm or reject those changes (e.g. suggesting a proper type if it can be determined from the data).
We also include revisions to variability types coming from the literature (published papers).
So, in short, the main source for the changes are the researchers, they take or analyze data for some object, determine a classification and submit it to VSX or publish it elsewhere. Then we adopt it in VSX after some feedback (if needed).

3)  Did this organization receive input from other organizations in determining that there were recommended changes to be made? 

As mentioned above the number of stars, revisions and information available does not require such input. Each day several new stars are classified/reclassified. This is daily routine now. There are objective criteria that -if met- are enough to correct classifications. We currently try to be such central repository of variable stars and to improve the available classifications.

4) has already been answered

5)  Is the process including the acceptance criteria that was used to make these changes described on a website or in some document? 

You can read the VSX guidelines to know more about how a revision should be made but basically, it has already been described above: we know the properties of each variability type and the proposed changes have to fit those properties, something that has to be proven with supporting evidence, mainly light curves.

6)  Were all of the organizations that were involved in the change process also approvers of the standard/document that described the change process that was used?

We could say that we do both things but I think you probably give too much importance to something that has now become routinary.
To mention your examples, most L-type stars (variable red giants) are actually SRB variables, that is, semiregular red giants with vague periodicity, usually with several periods beating against each other causing periods of irregularity in their light curves.
Decades ago we did not have enough data to be able to find any periodicity. Now with years of survey data available we can find it so the star meets the definition of an SR variable and the classification is changed.

In short, you will see reclassifications every day as part of our VSX work.
At the same time, papers are being published everywhere all the time with new classifications based on the known properties of the different variabilty types. And you and anyone interested can be part of this constantly changing knowledge too.

Cheers,
Sebastian

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Sebastian Otero

VSX Team

American Association of Variable Star Observers 

rglassner
Classification Changes

 

Thank you Kristine for the prompt response and thank you Sebastian for the very thorough explanation of how the VSX Team does their work.  I appreciate all that you both do in support of AAVSO. 

As a new observer of variable stars I am trying to learn all that I can about how things work.  The detailed explanation of the VSX Team activities helps to better understand the process that is used to make VSX classification changes.

Thanks again,

Rich  

 

 

 

 

LKR
LKR's picture
Kudos and THANKS to Sebastian & everyone else who works on VSX!

Thanks Sebastian for your thorough explanation! I don't think enough people realize how much work you and others do to update this valuable resource. A very big public THANK YOU!!!!!

 

KL
 

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