An entire class of variables may be misclassified

Tue, 11/08/2016 - 15:33

Recently it was suggested that I use BL Cam as a "First Star" attempt at variable star photometry. I am told that BL Cam is a SXPHE (SX Phoenicis variable) star which show several simultaneous periods of oscillation and variable amplitude light changes. Upon closer examination of BL Cam using TheSkyX star database add-on, the "star" appears to actually be three stars (topographic coordinates):

NOMAD (03h 48m 52.12s , +63d 25m 37.16s)
GSC 4067:471 (03h 48m 52s , +63d 25m 38s)
NOMAD (03h 48m 51.34s , +63d 25m 38.83s)

Screen prints of these are attached. The the simultaneous periods of oscillation and variable amplitude light changes of BL Cam may be the result of more than one of these stars varying sanctimoniously. My telescope cannot resolve each star individually and I suspect that most earth based telescopes would not be able to resolve these as individual stars, thus the mis-classification. Something like the Hubble might be able to study these stars individually.

Does anyone know if there exists somewhere a database of stars with which I can sort based on "type" in order to identify all SXPHE stars for similar examination? I would like to make a list of all such "stars" that might have been mis-classified for further examination.

Ed

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Affiliation
American Association of Variable Star Observers (AAVSO)
SUre looks like progression

SUre looks like progression of the star over the time period these measurements were taken.  In the digital sky survey there is only one star at the center of these coordinates.

Mis-classification of variable stars

I don't believe the DSS had the resolution to separate out these stars. I don't know that any earth based telescope can, unless possibly by using adaptive optics. Based on the coordinates these stars are extremely close, sub-one second arc between them. The HST could separate them easily.

Thank you for that reference.

Thank you for that reference. The photos appear to have about the the resolution of my telescope and at that resolution it does indeed appear to show one star. However as I zoomed in on it the images began to pixelate. I checked all the sources listed. I was not able to find a source with sub-arc second resolution. Did you find one? I am not familiar with the site and may not know how to use it properly. So it is possible there is a sub arc second resolution image there that I missed.

It is also certainly possible that TheSkyX Database addon is faulty. Based on what I have seen so far, however, I cannot determine which possibility is the case. I suppose the the bottom line is that I have yet to be convinced this is a single star based upon what I have seen.

Ed

Affiliation
American Association of Variable Star Observers (AAVSO)
One star, different catalogues

As others have expressed in this thread, what you are seeing is just the same star with slightly different positions in each catalogue due to different astrometric accuracy.
You will never find exactly the same position in all the astrometric catalogues, the only exceptions being HIPPARCOS and Gaia.
The differences you have found are pretty standard for the different catalogues.

Best wishes,
Sebastian

Affiliation
American Association of Variable Star Observers (AAVSO)
one star?

I would say that there is a high likelihood of these 3 separate sets of figures actually referring to one star, having come across this sort of thing several times before when making sequences. Not all catalogues are equally precise in every parameter, whether the stars are varying sanctimoniously or otherwise "Hah! You're not a proper variable star like I am..."

That is probably correct. I

That is probably correct. The GSC object could easily be a duplicate of one of the NOMAD objects. I do want to track down where that second NOMAD object comes from. It could be a problem with the software or a problem with the catalog. I am working with Software Bisque now to get their take on it.

Ed

Affiliation
American Association of Variable Star Observers (AAVSO)
companion stars

Hi Ed,

The first question, especially with NOMAD that goes to 21st magnitude, is how bright are the various entries that you list?  It is easy to have a 12th magnitude star (BL Cam) next to an 18th magnitude star (a companion), where the companion/neighbor is irrelevant.

Don't assume that any entry in any catalog is the absolute truth.  You have to look at the uncertainty on everything, including position and brightness.

I strongly recommend reading the AAVSO CCD Manual as your first exercise.  We're here to help!

Arne