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11.5 V transient observed near WW Cyg -- need help explaining!

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spcook
11.5 V transient observed near WW Cyg -- need help explaining!

During the middle of a three hour observing run last night Aug 12-13 2019 on EB star WW Cyg (with my 130 mm f/5 reflector ST6 CCD imager with V filter from Prescott, AZ site) I have one image (screen shot of 12 sec exposure taken with my iPhone attached) that shows a roughly 11.5 V object that looks like the other stars.

The image taken at 10:12 MST shows WW Cyg (very near center of image) at its min brightness around 13.2 V mag and roughly 60 arc sec to its slight upper left is the bright interloper. This image shows stars not round but slighly elongated east--west indicative of tracking error. That, and close inspection of pixel distribution for this object, rules out cosmic ray explanation and probably hot pixels.  

Quick inspection of a better image (with more rounded star images) taken 4 minutes earlier shows no obvious star in the subsequent bright interpolator position--nor do subsequent images 4, 6, 8 etc

Rough 2000 epoch co-ord of this transient are:

RA = 20 04 15

DEC = +41 36 16

Palomar sky survey visual image puts a very faint (mag 19-20) star close to this location.

If someone else happened to observe WW Cyg last night please come forward!

Likewise anyone with ideas / relevant experience as to how to account for this ? Most of the ones I can come up with seem far-fetched...

 

 

 

 

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spp
spp's picture
11.5 V transient

Could you please post the original FITS image which shows the transient but without the +.  The forums don't accept FITS images,  so just zip compress the FITS and attach the zip file.

spcook
11.5 V transient in WW Cyg two zipped FITS image files attached

Archive.zip contains two 81 KB two zipped FITS image files.  WW010 file image was taken four minutes earlier shows no trace of 11.5 V mag interloper that appears four minutes later in WW012 file

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pox
pox's picture
Well, we are in Perseid

Well, we are in Perseid season, so how about a face-on meteor?

spcook
Face on Meteor Perhaps Less Farfetched Than Other Explanations?

If I was teaching spherical astronomy I think I'd throw out the problem to students of whether a meteor originating from the Perseid radiant could have entered my telescope  pointing in the direction noted at the time noted to cause the transient interloper.  Without doing the math my gut assessment makes me  think it's possible! After years of seeing telescopic meteors and capturing many streaks on CCD images suggestive of them, if this CCD  image interloper is a face on meteor it would be a first! Thanks for the intriguing suggestion --- any spherical astronomy math / celestial mechanics whiz kids out there who want to take this problem? If not, perhaps I'll eventually dust off the old textbooks and tackle it myself!

spp
spp's picture
11.5 V transient

I've attached a screen shot of both images displayed in ds9.  The image with the "transient" is on the right.  The images are inverted (N down, E on the right).  I couldn't figure out how to annotate the image in ds9 to mark the transient.  It's near the lower right corner of the image.   The box at the upper right is zoomed in on the transient. The x,y pixel address of the single central pixel in the zoom box is shown in the table, so you can find the ROI easily if you open the ww.012 image.

Phil

daj
daj's picture
dumb question from me...

Cosmic ray hit?

spcook
Face on Meteor or Cosmic Ray or flare star?

My experience with cosmic ray produced additions  to CCD images is, on closer inspection, they don't look like stars. This interloper looks star-like including east-west elongation of shape due to poor tracking. I've thought typical cosmic ray impacts affect just one CCD pixel--although not necessarily especially energetic ones...As for a face on Perseid meteor: I'm now thinking, given the uncertain dust distribution spread out along orbit of comet Swift, etc  this is too complicated for some celestial mechanics based calculation to definitively establish.  And if the Earth is right there in the middle of max. dust concentration the Perseid radiant direction connection breaks down and meteors won't necessarily move in parallel paths that trace back to a point, but at least for a brief time appear more randomly? Anyway, although I'd like to think that's a star (maybe UV Ceti type?) far out there in space that produced a rare extremely bright flare my image caught, more likely is something going on right there on the CCD chip! I'm leaning toward a face on meteor and the fact this happened at a time close to the Earth's passing through the max. dust concentration related to comet Swift / Perseids suggests a Perseid connection. I'd say cosmic ray or hot pixel origins are much less likely. But I may never know for sure---unless during my next run on the eclipsing binary star WW Cyg I happen to see an event like this again in the very same spot!

Eric Dose
Eric Dose's picture
A cosmic ray artifact is best

Yes, a cosmic ray artifact is best identified by the sharpness of its edges, not by the number of its lit pixels.

The cosmic ray signal will go from high flux to zero net flux within one pixel edge, all around the artifact or almost so, whether it comprises one pixel or twenty; whereas a star will have visibly softer edges all around it (unless the image is woefully undersampled--very unusual for ground-based scopes).

SHA
SHA's picture
Satellite flash?

Is a flash from a satellite possible?  I've seen some quick ones that may not leave much of a trail.

spp
spp's picture
Image scale

I agree with the cosmic ray hit theory. 

At first glance, it seems unlikely that a random cosmic ray hit would line up so well with the star trails, leading us to look for other explanations.  But the image scale is about 7.9 arcsec/pixel.  With this image scale I think a cosmic ray arriving at an angle to the star trails could still produce an apparent path on the image which looks like a star trail.

Phil

Eric Dose
Eric Dose's picture
I don't think image scale

I don't think image scale (arcsec/pixel) in itself affects the size of artifacts from cosmic rays, as they are not focused by the optical path. Absolute pixel size (in microns) may well matter.

spp
spp's picture
image scale

Eric,

I was referring to the ability of an undersampled image to resolve a difference in direction between a short path (in this case 3 pixels long) of a cosmic particle travelling, with respect to the surface of the CCD chip at, say, 200 degrees as apposed to 160 degrees.  Both might look like 180 degrees. 

Phil

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