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OK, CV it is then. The sequence for AT 2019xim must have been added after I took the data, which is not surprising. My observations were completed within 48 hours of the ATEL being released.
My SOP for all variables except the very brightest is to take 30-second subs and stack in real time. That way I can estimate the SNR and move to another object when it is high enough or very obviously too faint to be measured with sufficient precision. Stars which can vary by several magnitudes between successive observations can easily turn out to be saturated or invisible if purely dead reckoning is used to set exposure lengths.
I took 100 minutes of unfiltered 30s images in the wee hours of 2020-01-20, though the SNR is so low that to get adequate SNR they will probably have to be co-added a few at a time. Another run took place on 2020-01-04. They, as well as some precision photometry in Johnson V and Sloan r´, still need to be processed. Perhaps this data is too early for the INT run; I will try to take some more in the next few weeks.
A question arises from our earlier discussion in the forum about the use of non-standard sequences for VS observations to be submitted to the BAA-VSS database. There is no standard sequence for unfiltered data. Advice would be welcome, whether here, in the original thread, or off-line via email. Another case without any standard sequence concerns the observations of AT 2019xim reported on my members page. I have specifically withheld submission of the results for this reason.
contains two, one at 143 and the other at 153. Both are inconveniently distant at around 15-20 arcmin (a guess from the chart scale – I have not measured them).
Personally I´d use them to measure the instantaneous brightness of other stars closer to the SN and then measure the SN with respect to them. If the images of the fields are taken within a few minutes of each other, it is very unlikely indeed that all the secondary comparisons are variable on that timescale, and not very likely that even one will be. If one or more is a LPV, who cares? It’s constant for all practical purposes.
If you discover that one or more field stars varies from night to night, that in itself is worth reporting.
I am now at the telescope taking a long series of exposures and a satellite or meteor just went through a frame. Very faint. Stars down to 17th mag are easily visible but the trail only just shows up above the sky noise. Guess 15th or so? It is going to be completely invisible in the final stack.
Not sure how relevant this is to the current discussion but it shows that we don´t need Starlink to be able to pick up the present vermin of the skies.
Good point.
Presumably one could monitor the field and avoid taking data during the satellite pass. Could be an interesting exercise writing software for motion detection in the autoguider camera.
How do you deal with satellite trails now?
Depending on whether I am doing photometry or imaging (which includes astrometry for present purposes) I either discard the sub before average-stacking or rely on median-stacking to discard the satellite for me. In either case, such concerns are of interest only when the satellite passes inconveniently close to the objects of interest, otherwise it is just ignored.
There again, I take as many 30 to 60 second subs as are needed to reach a satisfactory SNR (which depends on sky brightness, for instance) and then move on to another target. A cheap and simple way of optimizing the productivity of telescope time. Vary rarely does a single exposure exceed a couple of minutes.
I think that post can be counted as a success and that my client, often known as The Great Deceiver, will be well pleased.
You appear to have been led to believe that a reduction by a factor of pi in the number of degrees in the complete sky is an improvement. In terms of the average number of satellites per square degree, however …
😉
I am going to act as Devil’s advocate because someone should do so. The very phrase “Devil’s advocate” should indicate that my personal views are not necessarily in accordance with what I espouse below and in subsequent posts.
First, 4pi steradians is equal to 41,253 square degrees. We are already down by a factor of pi ( about 3.14) from your estimate.
Secondly. not all astronomers, professional and amateurs, are wide-field imagers. A good fraction of us perform precision astrometry and/or photometry. As long as any satellite trails (or cosmic ray hits for that matter) do not intrude on the object or its immediate neighbourhood, our work is completely unaffected,
More Pollyannish sentiments may appear in due course. This will have to suffice for the time being, not least because dinner is now being served.
“go to the website and register your observatory as a future participant mentioning in the ‘Comments’ box that you are an amateur astronomer and that you are joining the BAA Exoplanet Division’s initiative to support the ExoClock Project.”
Been there, done that.
Clear skies are erratic in these parts. It was (mostly) clear last night but with ferociously high katabatic winds so no observing was done. In those conditions the seeing is typically 15-20 arcsec and the scope flaps around on a similar scale, ruining tracking, even though it is inside a dome.
Not been very good here in LP either. To be fair I am only here half the year and I have had health and equipment issues which have curtailed my observing time, but even so …
I blame that Thunberg woman for drawing attention to global warming with its consequent increased cloud-cover, which itself arises from a larger capacity for the atmosphere to hold on to evaporated sea-water.
😉
Added in edit: the phrase “and equipment”
Thanks for your in-depth explanations. I´m learning!
Although I’m a molecular spectroscopist by background I am emphatically NOT an astrophysicist. You (personally, not the generic “you”‘) can´t resolve the rotational and any hyperfine substructure of the molecular bands, which is where I cut my teeth. Not entirely sure that anyone can. Betelegeuse is bright enough for spectral resolutions of 100K-1M (my doctoral work was at a resolution of around 300,000) but do the physical conditions in the star’s atmosphere allow that kind of line resolution? That was a rhetorical question. I would be delighted to learn that rotational structure is readily observable, not least because the effective temperature of any species in question could then be nailed down to a very few Kelvin.
Roughly half my DPhil thesis concerned the rotational structure in the spectrum of CeO at ~2300K. Its spectrum is mind-bogglingly complex for such a simple diatomic molecule. There are at least eight low-lying electronic states with populations high enough to exhibit absorption spectra at 2300K. Well over 100K lines in the absorption spectrum between 300nm and 1200nm were measurable with 1980´s technology. CeO is also known to be an atmospheric constituent of a number of cool stars.
If the radius dropped I would expect the temperature to rise, not fall, as the gravitational potential energy is converted to thermal kinetic energy.
Again, curious.
If the temperature had dropped I would expect the continuum to have shifted too — Wien´s law — though as that goes only as the first power of (1/T) perhaps the effect might be too small to be easily noticeable. I certainly haven´t noticed it from your spectra but there again, I don´t have much experience in these things.
I´m now wondering whether a neutral grey filter has interposed itself between us and the star. Something akin to the clouds of dust which appear in the atmospheres of RCB variables. The typical particle size would need to be significantly larger than the wavelength of light or we would see severe reddening.
Curious indeed.
You could try contacting the copyright holder, The Times presumably, and request permission to bring the article to a wider audience.
Yup.
All the professionals are going to be bugging us amateurs for telescope time because it saturates the detectors on all their equipment.
I see Robin and I posted pretty much simultaneously.
The neutrinos from SN1987a came in a clump a few seconds long. The telescope wasn’t very sensitive and the SN was at quite a distance so it’s likely that it saw only the very peak of the neutrino curve.
However, core collapse is a very rapid process, on the timescale of a minute or so (hence my prediction), and there is no obvious intense source of neutrino emission afterwards. Once the neutrinos get outside the core everything else lying in our direction is essentially transparent so they will not be scattered as is the initial burst of photons.
It depends entirely on how you look at it.
Neutrino telescopes will notice a great increase in brightness on the scale of seconds to a minute or few.
Optical telescopes will take a day or few, if the many thousands of other SNe which have been observed are anything to go by.
Betelgeuse already shows a disk if your telescope is good enough. It will show an ever bigger disk on timescales between days and millennia. Compare SN1054, the outside of which is now big enough to have been seen by Messier.
Good to see someone is checking my work to guard against errors. I should do the same for that of other workers.
My earlier post gave a time of 1957-May-19 21:35. Agreement is satisfactory.
Thank you. I’ve read that paper in the past, and imaged M67, but it’s good to read it again. Section 4 (p77) is particularly relevant, especially the comment about the difference between visual and CCD estimates of a 17.4 object when the image goes down to 20 or so. Another apposite comment is on page 79: This magnitude-bridging technique is common in the professional world, as most of the standard stars are too bright for large telescopes.
Please note that for present purposes I am emphatically NOT trying to detect the faintest possible object on the image. I am trying to measure the magnitude of the faintest object which has an error smaller than a specific limit, 0.1 magnitude say. In this case the SNR is way above the 5-sigma limit mentioned in the paper.
As I pointed out earlier, if I used a sequence which ends at 16.9 to measure a variable at say, 19.5 +/- 0.1 that estimate would be accepted without question. Why should a measurement to the same accuracy of an equally bright nearby star be rejected purely because it is not a (known) variable?
Behind all this is my firm belief that one should not throw away data. It should be preserved for later scientists to re-analyse if they wish. For my part I store every image which is not too badly corrupted by focus errors, guidance errors, passing clouds, etc. In only 18 months I already have more than thirty thousand images, together with their metadata in a SQL database. All can be retrieved and re-examined for whatever reason — pre-discovery observations, perhaps, or searching for previously unknown variables.
Don´t misunderstand me: I will continue to play by the rules as they stand but it seems to me that the present rule is extremely conservative to use Arne Henden´s phrase.
