Quote from: Star One on 04/02/2017 08:20 amThe rumour goes that there will be results from other observatories which will end this kind of speculation, as that's been the inference when others have made similar mistaken speculations.Can you clarify what the rumours are saying?
The rumour goes that there will be results from other observatories which will end this kind of speculation, as that's been the inference when others have made similar mistaken speculations.
Okay, with v-shape I mean the sharp bottom. The shadowing never remains constant. The asymmetries around is another big headache. The light curve has sharp dips that are suddenly cut off by a sharp rise. Is this characteristic for signals generated by electrical glitches?
What confidence intervals should one have in mind when looking at the light curve in Boyajian's paper? How good is the time resolution of the dips, could it be that they went down to zero for a few seconds?
Day 1559 the light curve in the paper is suddenly cut by half of a percent, when it reaches its highest level and during an otherwise calm period. Apparently some kind of recalibration. It makes me wonder about the 100 year and 4 year dimmings, how well calibrated they are. If one suddenly shifts the entire light curve by half of a percent every other year one might make up any kind of funny correlations. Or maybe there's no data because the curve looks flat before that drop? There are a couple of longer periods with flat curves, is there no data about potential dips there too? Like around day 805 just after the first clean big one.
What about the upside here? After day 1528 the star is up to almost 1% brighter than the normalized average. And not in any transiting manner. What could brighten a huge F-star like that by half of a percent steadily for two weeks? Or is the normalization off?
Quote from: TakeOff on 04/02/2017 12:32 pmOkay, with v-shape I mean the sharp bottom. The shadowing never remains constant. The asymmetries around is another big headache. The light curve has sharp dips that are suddenly cut off by a sharp rise. Is this characteristic for signals generated by electrical glitches?No, as has been said repeatedly, instrumental errors have been pretty much eliminated as an explanation. It was looked at very seriously, and the curve matches no conceivable fault.The space craft rotated 90 degrees every quarter, such that each target star is on a different CCD module, in a different orientation. Which means not only that different pixels are collected, but the optimal aperture for wach quarter is different as well. So any fault would have to affect *only* the pixels in the optimal aperture on 4 different CCDs and not affect any adjacent pixels. QuoteWhat confidence intervals should one have in mind when looking at the light curve in Boyajian's paper? How good is the time resolution of the dips, could it be that they went down to zero for a few seconds?No. The CCD pixels collect flux for 30 minutes (in long cadence). Then an overall flux value is created from a set of aperture pixels selected from the current pixel centroid and point spread function.QuoteDay 1559 the light curve in the paper is suddenly cut by half of a percent, when it reaches its highest level and during an otherwise calm period. Apparently some kind of recalibration. It makes me wonder about the 100 year and 4 year dimmings, how well calibrated they are. If one suddenly shifts the entire light curve by half of a percent every other year one might make up any kind of funny correlations. Or maybe there's no data because the curve looks flat before that drop? There are a couple of longer periods with flat curves, is there no data about potential dips there too? Like around day 805 just after the first clean big one.The processing of the curve (PDCSAP pipeline) is intended for transit detection and produces artefacts like that as a natural consequence of the processing - essentially the algorithm corrects for pointing errors and removes a moving-median from the curve (it is much more complex, but that is the essence), then normalises the values to "1".When looking at absolute flux, this curve (though easily accessible) is NOT reliable, and you need to calibrate against the full frame images (and other stuff).QuoteWhat about the upside here? After day 1528 the star is up to almost 1% brighter than the normalized average. And not in any transiting manner. What could brighten a huge F-star like that by half of a percent steadily for two weeks? Or is the normalization off?As above, this is a direct consequence of the correction pipeline and is not real (think how a moving median removal behave when there is a massive prolonged dip). As hop suggested, if you are serious, you need to learn how the instrument actually works and how it can fail.--- Tony
The space craft rotated 90 degrees every quarter, such that each target star is on a different CCD module, in a different orientation. Which means not only that different pixels are collected, but the optimal aperture for wach quarter is different as well. So any fault would have to affect *only* the pixels in the optimal aperture on 4 different CCDs and not affect any adjacent pixels.
QuoteWhat confidence intervals should one have in mind when looking at the light curve in Boyajian's paper? How good is the time resolution of the dips, could it be that they went down to zero for a few seconds?No. The CCD pixels collect flux for 30 minutes (in long cadence). Then an overall flux value is created from a set of aperture pixels selected from the current pixel centroid and point spread function.
What about the upside here? After day 1528 the star is up to almost 1% brighter than the normalized average. And not in any transiting manner. What could brighten a huge F-star like that by half of a percent steadily for two weeks? Or is the normalization off?QuoteAs above, this is a direct consequence of the correction pipeline and is not real (think how a moving median removal behave when there is a massive prolonged dip). As hop suggested, if you are serious, you need to learn how the instrument actually works and how it can fail.--- Tony
As above, this is a direct consequence of the correction pipeline and is not real (think how a moving median removal behave when there is a massive prolonged dip). As hop suggested, if you are serious, you need to learn how the instrument actually works and how it can fail.--- Tony
So the bottom flux of the light curve is unconstrained? Could it bottom out on -100%?Does the light curve really bounce from crashing to soaring within a 30 second period? From a star of about 2 million kilometer diameter.
So regarding the obvious lack of a steady repetition of the dips. Does it suggest (as seems the implication to me), that whatever is orbiting the star is speeding up, slowing down, and/or changing orbits between one orbit and the next? And also, is the star "lifting" hypothesis as presented by one theorist a few months ago still a potential solution, given the data as it stands?
Quote from: M.E.T. on 04/02/2017 03:53 pmSo regarding the obvious lack of a steady repetition of the dips. Does it suggest (as seems the implication to me), that whatever is orbiting the star is speeding up, slowing down, and/or changing orbits between one orbit and the next? And also, is the star "lifting" hypothesis as presented by one theorist a few months ago still a potential solution, given the data as it stands?Whatever blocked the light doesn't have to be in orbit of the star. It could be something like a gas or dust cloud in the interstellar medium. It could also be a comet swarm or something similar passing through the system or having been knocked onto a hyperbolic trajectory from the far reaches of the system by a passing star. It also doesn't have to be one single thing. A swarm of objects all in different orbits would make a pattern of dips that would look random until observed long enough to detect a pattern.
Quote from: notsorandom on 04/03/2017 02:18 pmQuote from: M.E.T. on 04/02/2017 03:53 pmSo regarding the obvious lack of a steady repetition of the dips. Does it suggest (as seems the implication to me), that whatever is orbiting the star is speeding up, slowing down, and/or changing orbits between one orbit and the next? And also, is the star "lifting" hypothesis as presented by one theorist a few months ago still a potential solution, given the data as it stands?Whatever blocked the light doesn't have to be in orbit of the star. It could be something like a gas or dust cloud in the interstellar medium. It could also be a comet swarm or something similar passing through the system or having been knocked onto a hyperbolic trajectory from the far reaches of the system by a passing star. It also doesn't have to be one single thing. A swarm of objects all in different orbits would make a pattern of dips that would look random until observed long enough to detect a pattern. Two Earth years apart explaining both the single very clean asymmetrical first deep dip, and then two years later also explain the pretty chaotic light curve including a couple of deep asymmetric dips too? Somehow anything passed between us and it, but never between us and any other star (as in 160,000 stars in the same telescope), in order to cause this light curve? Who can blame me for not buying that. I might've bought one of them, but not both.
Isn't it just as hard to explain why this purported observational error happens (many times, even!) only with this particular star?
Quote from: as58 on 04/03/2017 04:04 pmIsn't it just as hard to explain why this purported observational error happens (many times, even!) only with this particular star?Harder!This supposed error only affects pixels in the optimal aperture for the star, and only when those pixels are observing that star (one quarter a year) ... and the pixels are on 4 different CCDs in different orientations, and the aperture is a different shapes in each of the different quarters. Read-out errors are precluded due to this as well ... very much special pleading.--- Tony
I think we should split this thread into two separate threads.Thread A: For the one poster who thinks it's an observational error to argue with everyone else.Thread B: For all other discussions of Boyajian's Star exception debating whether it's likely to be observational error.I think the vast majority of people here are more interested in B than A and it's unfortunate all those people have to wade through so many posts that belong in thread A.
Should be a new SETI related paper from Jason Wright published Tuesday.https://mobile.twitter.com/Astro_Wright/status/856208078282178560
Quote from: Star One on 04/23/2017 09:13 pmShould be a new SETI related paper from Jason Wright published Tuesday.https://mobile.twitter.com/Astro_Wright/status/856208078282178560This is the paper: https://arxiv.org/abs/1704.07263(Not directly related to Boyajian's star, though)
Jonathan McDowell @planet4589Prior technological species. Jason doesn't address Dr Who's Silurians specifically, though. Jason Wright @Astro_WrightReplying to @Astro_Wright and @AdamFrank4(link: https://arxiv.org/abs/1704.07263) arxiv.org/abs/1704.07263Jason Wright @Astro_WrightReplying to @planet4589Only because none of my Whovian tweeps told me about them when I asked for examples! ;-)