Thanks.dyqik wrote: ↑Thu Sep 17, 2020 12:54 pmNo, you don't usually do it like that. I'm on vacation, so haven't spoken to colleagues in detail about this.basementer wrote: ↑Wed Sep 16, 2020 6:54 pmCould you clarify, dyqik, is it that a 12th order polynomial is usually used in this sort of analysis, although it's known to be tricky? Or that this is a novel technique that immediately looks risky?dyqik wrote: ↑Tue Sep 15, 2020 10:06 pmSome of my colleagues are not entirely convinced that the claimed detection in the paper is actually a spectral line. And they are among the world's experts on detecting molecules in planetary atmospheres with the telescopes in question, and one is acknowledged in this paper.
I suggest you look at fig. 3 first, then fig. 1 and fig. 2 in the paper.
Additionally, pulling the line out of the background involves fitting a 12th order polynomial to the spectra, which is a potentially difficult thing to get right and not contaminate the data with.
Is there life on Venus?
- basementer
- Dorkwood
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Re: Is there life on Venus?
Money is just a substitute for luck anyway. - Tom Siddell
Re: Is there life on Venus?
The paper says
The main limitation at a small line-to-continuum ratio (hereafter,
l:c ratio) was spectral ‘ripple’, from artefacts such as signal
reflections. We identified three issues (see ‘JCMT data reduction’
in Methods), with the most problematic being high-frequency
ripple drifting within observations in a manner hard to remove
even in Fourier space (Extended Data Fig. 1). We thus followed
an approach standardized over several decades, fitting
amplitude-versus-wavelength polynomials to the ripples (in
140 spectra). The passband was truncated to 100 km s−1 to avoid
using high polynomial orders. (Order is based on the number N
of ‘bumps’ in the ripple pattern; fitting is optimal with order N + 1
and negligibly improved at increased order. A wider band includes
more ‘bumps’, increasing N. For minimum freedom, a linear fit can
be employed immediately around the line candidate, ignoring the
remaining passband—see Table 1 for resulting systematic differences.)
We explored a range of solutions with the spectra flattened
outside a velocity interval within which absorption is allowed. (The
polynomial must be interpolated across an interval, as if fitted to the
complete band it will always remove a line candidate, given freedom
to increase order.) These interpolation intervals ranged from very
narrow, preserving only the line core (predicted by our radiative
transfer models, Fig. 1), up to a Fourier-defined limit above which
negative-sign artefacts can mimic an absorption line. Details are in
Methods, with the reduction script in Supplementary Software 1.
The spectra were also reduced completely independently by a second
team member, via a minimal-processing method that collapses
the data stack down the time axis and fits a one-step, low-order
polynomial; this gave a similar output spectrum but with a lower
signal-to-noise ratio
My avatar was a scientific result that was later found to be 'mistaken' - I rarely claim to be 100% correct
ETA 5/8/20: I've been advised that the result was correct, it was the initial interpretation that needed to be withdrawn
Meta? I'd say so!
ETA 5/8/20: I've been advised that the result was correct, it was the initial interpretation that needed to be withdrawn
Meta? I'd say so!
- Little waster
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Re: Is there life on Venus?
Simples they wanted the elephant to wave it's trunk.
This place is not a place of honor, no highly esteemed deed is commemorated here, nothing valued is here.
What is here was dangerous and repulsive to us.
This place is best shunned and left uninhabited.
What is here was dangerous and repulsive to us.
This place is best shunned and left uninhabited.
- sTeamTraen
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Re: Is there life on Venus?
Am I the only one who sees the title "Is there life on Venus" and thinks it could be the start of a short poem, possibly more suitable for broadcasting after the 9pm watershed rather than before?
Something something hammer something something nail
Re: Is there life on Venus?
Is there life on Venus?
It doesn’t seem too likely.
Does it have a penis?
It must be rather spiky.
It doesn’t seem too likely.
Does it have a penis?
It must be rather spiky.
where once I used to scintillate
now I sin till ten past three
now I sin till ten past three
- bob sterman
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Re: Is there life on Venus?
Chapeau!
And remember that if you botch the exit, the carnival of reaction may be coming to a town near you.
Fintan O'Toole
Fintan O'Toole
Re: Is there life on Venus?
There's no phosphine detected on Venus - paper including some of my colleagues among the authors.
Re: Is there life on Venus?
That’s a shame, but not completely surprising. I wonder how the original authors will react.
where once I used to scintillate
now I sin till ten past three
now I sin till ten past three