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A quick kick of the tyres left me impressed but there is something I spotted. Is the longitude positive going east or west? For instance, La Palma is roughly 17W. Is that longitude 17 or 343?
Tracie, I understand your concerns but my teenage observations were made from light-polluted suburban Derbyshire, not a dark site. Today, despite my aging eyes, I still have no difficulty at all observing it from home 10km due south of brilliantly lit Cambridge (the VS is circumpolar …) and in a garden lit by neighbours.
I do not know where Tracey’s members live in North Wales but I remember the skies being markedly darker (and cloudier) there than they were in Derbyshire and my guess is that they are likely darker than where I now live.
Much the same with me, but the other way round. TheSkyX is installed but, strangely perhaps, prefer The Sky 6. MaximDL 6 is used for camera control, including guiding. My experience is that it guides very well as long as there is a bright enough star within the field of the SBIG-8 / AO-7 AG combination.
For VS work I tend to take enough 30s subs to achieve an acceptable SNR and then move on to the next target. MaxIm DL’s stacking function is invaluable for this. Given that some variables can change by several magnitudes from night to night, my approach can save significant telescope time. To avoid confusion: Maxim DL is used only as a first-look eyeballing procedure, not for final analysis where a local installation of astrometry.net and SWarp is used for stacking.
Naked eye observations of delta Cephei introduces people to variable star observing. This particular star has the benefit of being bright (visible in light polluted areas), good comparison stars nearby, circumpolar (it doesn’t matter what time of year it is and so suitable for long-term observation) and varies markedly over a short time scale (conducive to making it interesting to beginners).
Pooling the results of several of your members will help bring out the variations more clearly and phase-folding observations made over a period of weeks or months should show the nice sawtooth light curve of a classical Cepheid.
Somewhere I still have the observations I made as a young teenager. It’s how I became interested in observing variables.
Linux can certainly run a telescope control system natively but you’d have to use alternatives to the packages with which you are familiar.
WINE is getting pretty good and may be able to run MaxIm DL et al. but when I tried to run Astrometrica under WINE on a Ubuntu 18.10 system it failed because of the lack of some critical component in WINE. You may have better luck.
An alternative to WINE is to run Windows 7 (or whatever you have) in a virtual machine. Again, it may not be completely plain sailing but it may work just fine.
I can go into much more detail but perhaps that’s best done off-line.
This is a question to which I genuinely don’t know the answer. Is some component of sky glow caused by long-lived excitation and relaxation (aka phosphorescence) of molecular species in the upper atmosphere? Some so-called forbidden transitions have a lifetime of the excited state measured in minutes or hours. A commonly encountered example is found in alarm clocks where the hands and figures can remain glowing for hours after the lights have been switched off.
This mechanism may be a factor in the sky become darker long after it has been directly illuminated as the phosphorescence fades.
I support the Dobsonian suggestion though, as noted, it’s not suitable for long-exposure imaging. Lucky imaging of planerts should be fine as each exposure is so short that trailing is likely to be completely overwhelmed by the seeing and / or diffraction. (Maximum drift is 15 arcsec per sec for an equatorial target, or 0.15 arscec at a frame rate of 100 fps where you would need almost a one metre aperture for diffraction to be an issue.)
Indeed, back in the day I kept an 18″ Dob. in my kitchen. Made of plywood, it was still a reasonable task to lug its two sections out onto the back yard for an observing session. Current designs are lighter still. There is absolutely no way that a traditionally mounted 18-incher could be regarded as portable.
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 …
