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V742 Lyr fading

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ThomasK's picture
V742 Lyr fading

RCB star V742 Lyr, former NSV 11154, seems to be fading. I measured it to 12.0 V in June. In mid August it had faded slightly to 12.4 V, but have since dropped to 13.8 V today (Sept 6). There have been some visual estimates since the fade started, but the visual observers seems not to have noticed any change. Maybe some more should have a look on this star.

Thomas Karlsson

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BRJ's picture
V742 Lyr Fade

My first impression after looking at the AAVSO's B and D charts for the variable, together with its lightcurve and the very recent divergence between visual and CCD determinations, suggest to me that visual observers may have been using too low a magnification to put broad separatition between the variable and its 12.9 magnitude companion. Failing to do so can often seem to  enhance the brightness of the former during the earliest stages of decline. I've seen this scenario played out multiple times over the years. Had it not been for the interruption from the moon nearing full, I would think that the visual observers would have taken notice of the decline right about the time of the last posted  "v" observation (obviously made under strong moonlight interference). Watch to see if things don't change by next week, when the moon is gone.

J.Bortle   (BRJ)


lmk's picture
Which companions?

John, the recent VSP chart I printed shows a 129 about 1.5 arcmin to the W, and a 131 abt the same distance to the NNW. Generally, "close companions" would be arcseconds away, and then may cause a problem with combined magnitudes, so I am not sure if these are the comps you are talking about or something else? (1.5 arcmin may cause problems for simple binoculars, but you can't estimate 13th mag with simple binoculars!)


ThomasK's picture
V742 Lyr fade

V742 Lyr fade continue, I measured it to 14.78 V last night. This is only the second fading of this star since it was re-classified as a RCB-star in 2011. In 2015 it reached 15.5, should it reach lower this time? Historically, it has reached magnitude less than 17 on plates from Harvard and Sonneberg.

spp's picture
New Ic magnitudes for V742 Lyr Comps

The Sequence Team has recently augmented the comp sequence for V742 Lyr with R and I standard magnitudes.  Now, 15 of the 16 comps have these, just in time for this dimming.  (Previously, only the three brightest AAVSO comps had R and I photometry.)  Thanks to the new sequence,  CCD observers with typical equipment should find it easier to make transformed magnitude estimates in V- I or V-R even as the star gets fainter.


ThomasK's picture
V742 Lyr still fading

I got V742 Lyr to 17.4 last night and very near my limiting magnitude. The star has not shown any signs of reaching the bottom yet. I urge everyone that can go deeper to begin cover this star in its unusual low state.

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