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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.
My submissions to the DB include measurements of the full sequence. Accordingly, I don´t see why confusion should happen. If the sequence changes, through the addition of fainter members perhaps, all significant information is present to reduce to the new sequence.
For the example given, a snippet of an entry would look like
VarAbsMag VarAbsErr CmpStar RefMag RefErr CMMag CmpErr
[19.6203 0.0123 169 16.862 0.022 16.765 0.0095
where everything other than “169 16.862 0.022” is fictitious, invented as an example, and the CmpStar through CmpErr fields for the rest of the sequence have been omitted here for brevity; they would be present in the true submission.
Each of plates 6 & 7 are of Bennett, taken mid-April 1970. Can´t be more accurate without better astrometry.
Incidentally, http://www.icq.eps.harvard.edu/bortle.html is an invaluable resource. I use Norton’s 2000 to convert Bortle’s constellation names into approximate RA/Dec for comparing with plate solutions given by Lars.
This the JPL ephemeris of Comet C/1956 R1 (Arend-Roland) for the night of 1957-05-19/20
1957-May-19 21:00 A 07 03 54.81 +63 27 41.3
1957-May-19 21:10 A 07 03 57.35 +63 27 39.2
1957-May-19 21:20 A 07 03 59.89 +63 27 37.1
1957-May-19 21:30 07 04 02.43 +63 27 35.0
1957-May-19 21:40 07 04 04.97 +63 27 32.9
1957-May-19 21:50 07 04 07.50 +63 27 30.8
1957-May-19 22:00 07 04 10.05 +63 27 28.7
1957-May-19 22:10 07 04 12.59 +63 27 26.5
1957-May-19 22:20 07 04 15.13 +63 27 24.4
1957-May-19 22:30 07 04 17.67 +63 27 22.3
1957-May-19 22:40 07 04 20.21 +63 27 20.1
1957-May-19 22:50 07 04 22.76 +63 27 18.0
1957-May-19 23:00 07 04 25.30 +63 27 15.9The crude position I gave earlier suggests that mid-exposure was close to 21:35 UT.
Lars: do you have precise postions for the other plates? If so, please post them and I’ll happily do the detective work. If not. it will take me a little time.
Lars didn´t post the precise positions of the comet nucleus. I could do so but don´t know if he intends doing so and I don´t really want to duplicate his efforts. If you have even a rough guess at the epoch for each plate the precise position should nail down the date and time of mid-exposure to a few minutes.
I’m no good at identifying comets but I do know how to drive a plate solver. A local install of astrometry.net with the Gaia-DR2 database turns up the following for “Plate 1”.
RA,Dec = (111.067,63.945), pixel scale 20.1561 arcsec/pix.
Field center: (RA,Dec) = (111.072006, 63.929675) deg.
Field center: (RA H:M:S, Dec D:M:S) = (07:24:17.281, +63:55:46.828).
Field size: 3.21749 x 4.45504 degrees
Field rotation angle: up is 114.772 degrees E of N
Field parity: neg
Eyeball astrometry of the image gives a J2000 position for comet’s nucleus as 07:04:43.7, +63:26:31. Please feel free to precess that to B1950 if it helps identify the comet.
Looks like it might be clear again tonight. If so, solving the remaining prints will give me something to do while waiting for the photons to come in.
I understand what you are saying but it goes against the grain to throw away information. Here’s my reasoning.
Suppose that on the night in question SV Ari was at V=19.45 and that I had easily enough SNR to measure it to an accuracy of 0.01 magnitude based on an extrapolation of the sequence magnitudes down below 169. I would report a positive result.
Suppose that a field star was also measured on exactly the same image at, say, V=19.61, also to an accuracy of 0.01 magnitudes. I feel I would be justified in recording it as such, if only in my own records. Note whether or not that second star is a variable is irrelevant because it is being measured at a specific point in time.
Now, a week or so later, SV Ari has faded to a true magnitude of, say, V=22.0 which is way below the detection limit. However, that same field star is still measurable on an image taken at the later date. For the sake of example, let´s say it is now measured at V 19.62 with accuracy 0.01, again using only the official sequence. It is quite irrelevant in this particular instance whether that star has truly faded slightly or whether the difference between the two measurements arises for SNR reasons. It is quite clear that SV Ari at this date is significantly fainter than V=19.6. It seems wrong to me to throw away the additional information about the limit on the brightness of the variable.
Please note, in the latter case, I would NOT be using the V=19.6 star as part of the sequence to determine instrumental magnitudes and their errors. All of that is still being done exclusively with the standard sequence through a lengthy extrapolation.
Yes, I´m quite prepared to work with Jeremy and/or the AAVSO to extend the sequence in this case and others. However, prospective additional sequence members will need to be checked that they do not vary significantly on timescales ranging between hours and years before they can be used with confidence. (This issue has already bitten me: I discovered that one of the AAVSO comparisons for V3721 Oph is an EA with minima 0.025 and 0.010 magnitudes.) My suggestion, on the other hand, requires no assumption of constancy, only that the limiting magnitude can be measured at the time of observation.
Geosynchronous satellites have been plentiful for decades now. The good thing is that their orbits are known precisely and their ephemerides are widely available so that you can take your images at times when they are absent. Further, they are confined to a small strip of the sky so there are many other areas to image without their intrusion.
The real err… persons born to unmarried parents, are the likes of the Starlink constellation. IMAO, anyway.
