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“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.
I make at least seven, most of which are quite faint. The pixel coordinates are close to (913,646), (708,707), (235,482), (274,843), (697,140), (939,483) and (562,850). This was only a casual inspection and there could well be more with a detailed search.
Hmm. Could be fun to write code to find these things.
That’s what the market seems to need these days in order to remain financially viable as a main-stream publication.
More credit to The Astronomer for remaining true to its readership. No glossy adverts, no dumbing down.
Of course, I’m just a reactionary elitist old-fart^H^H^Hogey
It’s happened 4 weeks too early for me. Not back in La Palma until mid-February, where I can reach mag 20 or better with around an hour’s exposure. Can’t even reach mag 8 from here.
Oh well.
I seem to remember seeing the Pup on (a very few) occasion(s) with the 0.275m Mak-Cas owned by the Oxford University AS. This would have been around 1980 or so, My memory is suspect and I no longer have access to any contemporary records so treat this report with the suspicion it deserves.
Interesting.
In February I picked up a copy of Astronomy Now on a whim, the first one I’d read in almost 30 years. Inside was an advert for a house and observatory for sale in La Palma. We bought it in the summer and much of August was spent learning how to drive the 0.4m Cassegrain, a SBIG-8 camera and assorted gubbins. A second spell 30 Oct through 10 Dec was an opportunity to do some science, almost entirely CVs and SDOR variables, though I did get some nice images of Sirius B and Sycorax (aka Uranus XVII). Not yet processed are images which I hope will show Nereid clearly. Plans for 2019 include tracking down other small satellites in the outer solar system.
On 2018-11-30 I was imaging HL CMa, which many of you know is uncomfortably close to Sirius. It’s essential to place the latter outside the field or it dazzles both CCDs and eyeballs. However, at least there is a bright (far too bright) guide star nearby. A SBIG-8 camera has a small CCD for guiding purposes and it was used with the minimum possible exposure time of 0.11 seconds. Sirius was still over exposed but, to my surprise, the Pup showed up occasionally in the autoguider window.After taking the science data another 100 images at 0.11s were taken of Sirius. The one from the moment of best seeing appears here. The blooming from Sirius runs from top to bottom on the full frame, of which this is only a small crop. It’s fortunate that the camera was orientated at a good angle to the line joining the stars.
In The Fine Manual for DAOPHOT, available as http://www.astro.wisc.edu/sirtf/daophot2.pdf , the PSF question is covered in detail. A quote from page 32 reads:
For all the different analytic first approximations, the first two parameters are always the half-width at half-maximum in x and y. Any other parameters the model may have differ from function to function, but the first two are, as I say, always the half-width at half-maximum in x and y.
Accordingly, the PSF is invariably elliptical.
See, also, the ALGORITHMS section of daophot> help psf where it is explained that if varorder >= 0, the residuals from the fit are stored as a lookup table, meaning that all but pathologically weird shapes can be handled with ease. In particular diffraction spikes from secondary mirror supports cause no difficulty whatsoever.
I freely accept that DAOPHOT isn’t user-friendly by modern standards but it does a superb job.
It looks like I may now have a portable photometry toolkit which should run most anywhere as the components are written in Java and Perl.
The raw input data is a FITS image to be analyzed and an AAVSO CCD-photometry chart downloaded from aavso.org then saved in HTML format. The latter is first parsed into a couple of plain text files, one of which is a list of sources to be found and analyzed by APT, the other a summary of the data for the comparison stars.
APT is then instructed to perform the aperture astronomy and write a CSV file of its findings. The latter is then processed by a Perl script to produce a TSV file suitable for submission to the BAA-VSS — or so I believe.
Would anyone like to be a beta-tester of this stuff? It’s limited but apparently functional. It should run anywhere with a Perl installation and a Java Virtual Machine but that hasn’t yet been proven.
Extensions to use AIJ (and possibly other photometry engines) are planned, as is smoothing out rough edges.
Please mail me for source code and hand-holding. You’ll need the latter as the documentation for my stuff is non-existent at present (that will change), though the code is well commented. APT is very well documented.
Paul
The photometry tools which run everywhere and with which I have some familiarity are APT, AstroImageJ and IRAF/DAOPHOT. Those are the ones which I will target. AIJ will be familiar to many here; I’m climbing its learning curve with the assistance of the excellent BAA-VSS guide. As noted above, I like APT. DAOPHOT is the grand-daddy from which most other tools have been developed, including munipack/muniwin (another excellent tool but not one with which I’m currently playing).
DAOPHOT is a real professional’s tool. I’ve scripted it to analyze approximately 10k images taken over the last several months by Kevin Hills. It’s a refugee from the 1980s and doesn’t fit particularly well with the GUI paradigm. I’m an old fogey so that doesn’t worry me too much. What I really like is that although it uses only circular apertures, the star PSF is evaluated directly from the data (that is it doesn’t assume any particular shape and so can handle trailed or otherwise munged images) and can vary from point to point in the image. Coupled with very effective de-blending of closely neighboring stars, it gives very accurate results even in very crowded fields.
As far as I can tell (please correct me if I’m wrong) AIJ employs only circular apertures and assumes that the star images are circularly symmetrical. If so, a trailed star has to be included inside a relatively large circular aperture and so encloses rather a lot of sky as well, leading to poorer estimates for the magnitude and its error.
APT (again, AFAICT) doesn’t allow for a spatially-varying PSF but does allow apertures which are ellipses of arbitrary orientation. As well as modelling non-circular stars nicely, this also fits well with the requirements for performing photometry of galaxies (and perhaps comets?).
Software written so far will parse a downloaded AAVSO CCD photometry file and produce target lists for APT and a RADec file for AIJ. Still to come is code which replicates the BAA-VSS Excel spreadsheets which (again, AFAICT) run only on MS Office.
Code to drive IRAF/DAOPHOT and Munipack is likely to take some time because I’m probably only the person interested in them
To early to ask for beta testers but your time will come!
