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Extreme values

roe
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While perusing some light curves I noticed a couple of vis measurements at mag 19 ( to one decimal place!).  The comp star claimed was at mag 18.1.  I reported these to HQ via zapper and will let the experts decide what to do with them.  But I'm wondering how big a telescope is needed to reliably view (with a human eyeball) 19th mag stars? (The key word here is "reliably.")

At the same time I noticed many "less than" measurements in the same range for this star (but as CCD values).  Many of these showed no chart  nor comp star value.  There were also many with comp stars and check stars 5 to 7 magnitudes brighter indicating extreme extrapolation.  How valuable can these measurements be?  I'm guessing that an experienced researcher would ignore them but is it worth the effort to try to clear them out of the AID?

Jim Roe [ROE]

Not amateur scope
lmk
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roe wrote:

While perusing some light curves I noticed a couple of vis measurements at mag 19 ( to one decimal place!).  The comp star claimed was at mag 18.1.  I reported these to HQ via zapper and will let the experts decide what to do with them.  But I'm wondering how big a telescope is needed to reliably view (with a human eyeball) 19th mag stars? (The key word here is "reliably.")

I can reliably estimate stars visually in the mid-16th magnitude range with my 20", so simply scaling up to 19.0 would require a 63" telescope. Given the issues of optical quality at these sizes and the practical seeing conditions limiting useful magnifications, it may require a little bigger than that even. Given that the largest working amateur reflector is around 50" (and very few larger than 40"), clearly any such estimates must have been made visually with large observatory instruments!

Mike LMK

Or image enhancement!
lmk
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Oops, I forgot the possibility someone may have used the intensified "electronic eyepieces" such as the Collins i3, or observing visually from a computer monitor, with the larger dob style instruments. But I've never used these and not even sure if such could be properly classified as a "visual" observation? I think star color-related estimation problems would be a serious issue if such were used unfiltered.

Mike LMK

Mis-stated obstype
Matthew Templeton
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Hello Jim and Mike,

These are eye estimates from images taken by a camera (Slooh, I believe), rather than a visual estimate at the eyepiece.  They were submitted as "visual" but should really be CCD -- they're the equivalent of making a visual estimate off of plates.  When Sara Beck gets the Zapper notification, I'll ask her to modify these to have a different obstype.

Matthew

Extreme Measurements
roe
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LMK wrot:

" ...clearly any such estimates must have been made visually with large observatory instruments!"

Or not? ;)

Jim [ROE]

extreme values
HQA
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roe wrote:

At the same time I noticed many "less than" measurements in the same range for this star (but as CCD values).  Many of these showed no chart  nor comp star value.  There were also many with comp stars and check stars 5 to 7 magnitudes brighter indicating extreme extrapolation.  How valuable can these measurements be?  I'm guessing that an experienced researcher would ignore them but is it worth the effort to try to clear them out of the AID?

Hi Jim,

I don't know which objects you are referring to, so I don't know the comp stars in question.  I can imagine the case, for example, where there are only comp stars down to, say, 13th magnitude, because the chart was generated for an object in outburst.  In quiescence, it might be, say, 18th magnitude, which would be the 5 magnitude spread you mention.  if you believe that CCDs are linear, then a fainter than for a star 5 magnitudes fainter than the faintest comparison star is possible, such as nearly saturating that comp star or stacking lots of images to increase the dynamic range.  Professionals often throw away ALL fainter-thans, and are only interested in actual detections, so I've strongly recommended before, and am doing so again, that observers take the time to expose long enough to detect the object, even if it means fewer fields per night - the data is more valuable.  I don't think there is any need to clear fainter-thans out of the AID; they represent an attempt to measure an object without success and are useful in many cases, just not as useful as an actual measurement.

Arne

  Quick Check.   Yes!
WWJ
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Quick Check.

 

Yes! The “Telescope Limiting Magnitude Calculator” I have here, suggests an aperture of 100” at x500 would be required to view a 19.0 mag star under normal conditions. Go to Mt Wilson!

 

Ones often impressed by the law of diminishing returns, in these matters.

Faint observations
BSJ
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Thank you for bringing this to our attention, Jim. I am contacting the observer and will change or annotate the observations as appropriate when I hear back.

-Sara

AAVSO 49 Bay State Rd. Cambridge, MA 02138 aavso@aavso.org 617-354-0484