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I suggest that you send this to Roger for the “literature watch” section of the news letter. Although I started that idea, others’ contributions are always welcome.
Declaration of ulterior motive: anything which makes my life easier …
Should be easy enough to do. Point your scope at the celestial pole which is above your horizon. Take an hour-long exposure every month or two. Use your favourite astrometry software to find the centre of the star image arcs. Plot the results in a coordinate system where the start (or centre or end) of each arc is fixed. Precession is ~20 arcsec / year, easily measurable by anyone capable of arcsec precision. Note that this approach neglects the proper motions of the reference stars, which is likely to be accpetable onver the timescale of the project.
I’d try it but my fork-mounted scope can’t be pointed much above +75 Dec. That said, it might be a fun project for another scope which is (a) on an GEM and (b) not used for anything right now.
Thanks for giving me the idea!
A few months ago I discovered an EA variable in images taken by Kevin Hills where the primary minimum is around 25 mmag and the secondary is about 10 mmag. Not an exoplanet discovery in this case but well within the range of variability resulting from exoplanet transits, which tend to lie between 5 and 30 mmag.
I’m with Roger on this one.
Added in edit: I should analyse the rest of Kevin’s data to see what else turns up.
Thanks Nick, they are beautiful.
When I get chance (not for a couple of weeks or more) I’ll write a circular-arc Hough transform to find the NCP in each image. Assuming it works well I’ll make the source code available here.
Variables. I spend a few minutes on one target, then perhaps 20 on another, then off to another. Repeat for a few hours.
Setting the dome and letting them drift is the essence of my request. There are a few dozen eruptives in the BAA-VSS program. In what order should I observe them on a given night so that they drift past the open slit which has been set to a particular azimuth? Ordering by increasing RA is useful if the azimuth is 180 degrees and the declination is south of +28 degrees (my site is on La Palma at 28N) but many variables are at much higher declinations. In practice my chart collection is ordered primarily by RA (in 30 minute zones) then by Dec, south to north. I just flip pages in the binder and observe in order. It’s not a bad solution, by and large, but neither is it a good one if the objects are at high Dec or far from the meridian.
Of course, another approach would be to persuade the BAA-VSS to adopt some variables which barely rise from 52N. Somehow, I think I may have difficulties with that one. 😉
I intend to, but it’s as well as, not instead of. IMO, it’s always a good idea to minimize mechanical wear and tear.
This is the raw light curve. Purple shows the measure fluxes and their error bars. Green lines connect the points. A period of missing data and the existence of two (high measured flux) outliers is readily apparent.
The only processing performed is raw photometry with APT and a Perl script to normalize the photon flux to a comparison star. Absolutely no smoothing, outlier-removal or any other kind of data munging has been performed. The x-axis is HJD-2458551. The predicted ingress was for 2019-03-08T23:52 and egress at 2019-03-09T02:36. In JD these are 2458551 + (0.4944, 0.6108) respectively.
To me it appears that the ingress was picked up nicely. At about mid-eclipse I found that the dome wasn’t tracking properly so the data there is either noisy or missing. Towards the end of the eclipse the target had sank to an altitude of <35 degrees and further adjustment of the dome was neede (the slit exposes either the top 60 degrees or the bottom 60 degrees). In addition, the high winds made the scope flap around so much that the autoguider couldn’t cope and several more images were lost. The eye of faith suggests egress was detected but that may just be wishful thinking.
Detailed analysis will take place in due course.
Thanks. Initial measurements suggest that the actual precision is around 3.5mmag. Seeing was so bad that the aperture is 12 pixels in radius, and at 1.4arcsec/pixel that corresponds to a disk half a minute across! FWHM is markedly smaller, of course, but still far too big. Perhaps observing in Sloan-r might be an improvement.
It’s even windier today and I’ve serious doubts whether it’s worth even opening the dome. Incidentally, the gusts last night were strong enough to make the scope flap around beyond the ability of the autoguider to track correctly when observing at low altitude late in the session. I lost around 5% of the data to that cause.
“Incidentally, which exo are you trying.” Perhaps that is best kept firmly swept under the carpet for the moment.
Now trying again with WASP-65b. Predicted ingress is 23:52 with a depth of 0.0138 magnitudes. After much careful calibration 50 second exposures produce a SNR of~900 on an unfiltered CCD and imaging started at 23:00. My guess is that should give adequate precision (around 1.1mmag all being well) at a useful cadence. OK, it’s not in a standard photometric band but it’s close enough to GAIA-G and will do for a first attempt. I’ll be happy if anything decent looking shows up in the light curve.
Seeing is appalling right now, with stellar images at 8-15 arcsec FWHM. Strong north-easterlies blowing over the Canaries and as they pass over the caldera and cumbre a great deal of turbulence ensues down here at 760m altitude. The lucky guys at El Roque are above all that at 2600m. Perhaps it will improve later during the night but knowing my luck, it won’t.
I’m not sure about the apertures of those scopes. Could you enlighten me please?
Experience from my Sycorax adventure last year suggests that 21.0 or brighter should be possible with my 40cm unfiltered iand with decent seeing. When the seeing is >10 arcsec, which it has been quite often recently, dilution by sky background can be substantial.
Despite my “silliness” quip, is there any value from taking unfiltered measurements? If so I may repeat the experiment as I’ve essentially no interest in taking images of no scientific importance. If there were a SN in M88 to be discovered on the other hand …
I’d love to contribute but, sadly, my fork-mounted scope can’t see anything north of about 70 degrees. The safety cut-out, quite rightly, prevents me from scraping the camera off the end of the OTA.
I generally measure things in attoparsecs, one of which is about the distance between the end of my thumb and its first knuckle. Femtoparsecs are useful for measuring car journeys.
Densities should always be quoted in international standard carats per cubic fathom.
I thought everyone knew that the speed of light is a foot per nanosecond to an adequate accuracy. It’s all you need to know if you want to make delay lines from optical fibre. Remind me someday, when you’re especially bored, to recount the time when I helped build a photon time-of-flight spectrometer. (It should be well known that the speed of light depends on wavelength ;-). The guy who designed and did >90% of the construction had a peer-reviewed paper published in a reputable journal.
Much better seeing last night so had another go, taking images in several filters to see if that would enhance the contrast.
Nothing obviously visible but I’ve some software in development which may help. All that’s needed now is a copious supply of round tuits.
Title deliberately ambiguous. Excellent astronomical seeing is essential for a visual observation, as are precisely aligned and scrupulously clean optics. However, I wasn’t expecting to see Procyon B through an eyepiece. Like the travails reported by David Swan, swapping a camera for an eyepiece is too much of a faff. Actually, it isn’t, it’s the reverse that’s painful — having to spend hours taking all the flats in all filters again because the CCD will undoubtedly have rotated from its previous position.
No, I was planning on Lucky imaging to let me see the companion.
Hmm, perhaps it’s time to retake the flats anyway …
La Palma is famous for its dark skies, right? Not last night. There was a brilliant moonlit Calima. I didn’t even bother counting stars because a single glance showed that I’ve had much better skies from central Oxford or Cambridge.
It didn’t stop me observing variables but the limiting magnitude was markedly poorer than usual.
My scope is mildly odd in that the only optical surface exposed to the sky is a plane parallel disk of glass which serves two principal purposes. One is to keep dust, wee beasties, etc out of the way. The other is to support the Cassegrain secondary without introducing nasty diffraction spikes.
Dew is kept at bay by a very feeble heating element wrapped around the end of the tube and which doesn’t appear to cause any annoying air currents. Such a device could easily be used on any scope with an exposed front surface.
Now that we’ve had several images of Sirius B posted, including today’s picture of the week, does anyone fancy trying for Procyon B? The separation is only about half that of Sirius, so it will be much more of a challenge. Although the primary is 2 magnitudes fainter, so is the secondary.
I intend to give it a try after returning to La Palma this week.
I’d use Perl myself but de gustibus non disputandum est. Further, I already have code to process Daophot and APT output and extending it to SExtractor shouldn’t be difficult. My comment was more about the image processing end of things, to see whether a targeted approach optimised for just the one problem could be better (by some measure) than a general purpose tool.
