robin_astro

There is little "magic" in this though as far as I can see. The entangled pairs are merely being used to reduce the background noise so that every photon counts. The image has only a single bit depth (black or white) and the rest is image processing based on assumptions or a priori knowledge about the image. Cheers Robin

I was thinking of something much more prosaic. To completely reconstruct an asymmetric object we need to view it from different angles. For example from here on Earth we cannot tell what the reverse side of the moon looks like. Or with a galaxy, observations from a different viewpoint would reveal more about the internal structure. .

Then of course this only tells you about what the object looks like from a particular viewpoint. To know everything about the light from the object to the highest precision you would have to collect all the light. Anything else is just an approximation (Anyone else watch DEVS ? 😉 )

Due to the random nature of photons, to measure the brightness (flux) from the object to say 1% you need 100^2 = 10^4 photons To resolve the object into say 100x100 spacial points you then need to do this for 10^4 points so you need a total of 10^8 photons If we then also want to know the spectral distribution ie the distribution of energies emitted, we then need to know this for each wavelength. If we resolve this from say 4000 to 7000 Angstrom (visible light) at say 1 Angstrom intervals we need to do this 3000x so our total photon count is now 3x10^11 This is for one instant in time. If you want to know how it changes with time you then have to repeat this for each time interval Note this assumes perfect noise free detectors and no interfering photons from other sources Robin

This 2017 paper on IBEX observations ? https://iopscience.iop.org/article/10.3847/1538-4357/aa5cb2 In the conclusions they say that they have been able model the structure qualitatively including the split (without needing to invoke any unseen companion) though the paper is way to specialist for me to follow "Qualitatively, the characteristics of the global ENA fluxes are reproduced in our simulation, showing the "split" of the heliotail ENA structure occurring between ~1.74 and 2.73 keV consistent with the data. The heliotail ENA structure splits into the north and south ENA lobes near ~2 keV due to the inherent properties of the IHS plasma, suggesting a temperature of (slow SW) PUIs transmitted across the TS of ~107 K." Robin

Should be some first-hand accounts of 1987A eg an account of the discovery retold here http://www.oasi.org.uk/Misc/SN1987A.php

Nice result. Next step where the stars have similar features (or you have a template) or are you are following the same star for binary orbits for example could be to use cross correlation which gives potentially a much higher precision and is less sensitive to SNR. The technique is very powerful but it only gives a differential result though unless one of your stars has a known RV. ISIS has a tool for this and the procedure is described here for example in the workshop tutorial "Observing with a LISA spectrograph" here https://www.britastro.org/downloads/15701 where a 1 sigma precision ~1/40 of the resolution was achieved with careful attention to detail Cheers Robin

A bit late to the party but this calculator can be used to estimate the SNR for a particular setup, conditions and exposure http://spiff.rit.edu/richmond/signal.shtml Cheers Robin

Wavelength calibration based on lamps taken before and after the star spectra are usually good enough for amateur work but if you need higher absolute accuracy andthe spectrograph is stable enough to make it worthwhile, there are a number of catalogues of RV standard stars, for example this list of bright northern hemisphere targets on the ESO website https://www.eso.org/sci/facilities/lasilla/instruments/harps/tools/observing_tools.html but any non binary main sequence star and the RV figure given in SIMBAD should be good enough for most purposes. For Be stars at high resolution around H alpha I would recommend rather than calibrating using star spectra, using a simple neon lamp to get the dispersion equation and then use the atmospheric water lines to trim out any offsets which can be done to high accuracy. Visual Spec, ISIS for example have nice tools to do this and the BeSS validation team use these lines to check the calibration when validating spectra for the database. Cheers Robin

See here on Christan Buil's page an extreme example where the lamp is mounted in front of the telescope aperture and the line shifts depending on the position of the lamp (about halfway down the page) http://www.astrosurf.com/buil/isis/He_calibration/method.htm

Small wavelength shifts can sometimes be seen in spectrograph lamps depending on the illumination of the slit (In commercial instruments the light from the lamp is diffused either scattered off a separate surface in the case of the ALPY or by a translucent cover over the lamp in the case of the LHIRES to minimise this effect. ) These shifts are normally very small though (just a mainly an asymmetry in the shape of the line, rather than several pixels as here. Is the effect repeatable ? ie are you sure it is the lamp orientation which is causing the shift and not some other movement in the instrument as you adjust the lamp. (The LHIRES was notorious for this if all the screws were not tight, the slightest touch could move the lines) Note though that you cannot rely on the lamp for very high absolute wavelength calibration in any case as there are always some systematic differences between the lamp and the sky due to the different light paths. For high absolute accuracy RV measurements (rather than measuring relative changes eg in binary system) you calibrate out any systematic offsets using measurements of RV standard stars Cheers Robin

Nice result. Did you allow for the change in the radial component of Earths orbital velocity between the dates ie make any heliocentric corrections? Cheers Robin

Yes PNV means Possible NoVa to distinguish it from PN which means Planetary Nebula (and PSN which means Possible SuperNova) eg on the CBAT TOCP http://www.cbat.eps.harvard.edu/unconf/tocp.html Cheers Robin

Or if you want to think of it in terms of the warping of spacetime, the warping is only sufficient to prevent the photon escaping when at a distance from the singularity much smaller than the radius of the original star

You are confusing the strength of the gravitational field (which depends only on the mass and is therefore unchanged by the collapse) with the force felt by an object in that field which is proportional to the mass and inversely proportional to the square of the distance. After the collapse the mass is concentrated into a single point so you can venture much closer to the centre of mass, compared to when it was a star, where the force is much higher, until eventually at the event horizon it is high enough to prevent escape of the photon

For a collapsed star the diameter of the event horizon is much smaller than the diameter of the original star so any photon emitted at the same location as the surface of the star was would have no difficulty escaping even after the collapse. After collapse, as you get closer to the black hole the force of gravity increases as the inverse square of the distance to the point where at the event horizon the photon cannot escape

Don't forget to add your Be star spectra to the BeSS database http://basebe.obspm.fr/basebe/ and consider adding other targets to the BAA database https://britastro.org/specdb/data.php Cheers Robin

Nice resolution! Did you need to refocus for the different wavelengths ? Cheers Robin

Taken last night using the ALPY 600 Spectrograph guider image Processed spectrum here https://britastro.org/comment/7756#comment-7756 Cheers Robin

The long term trends for V,H and J do indicate though that The H,J IR bands have similarly been unaffected by previous dimmings suggesting we may well just be seeing a similar pulsation driven dimming though deeper than normal.

That is what the AAVSO data is suggesting. One caveat though is that the last two points were taken by the same observer who's name does not appear in earlier data so I would be interested in any corroborating evidence. There is some suggestion from I band spectrophotometry done using a Star Analyser that the drop in brightness reduces into the IR https://www.cloudynights.com/topic/645652-betelgeuse-is-faint-for-it/?p=9904083 (part of a long thread with lots of other discussions and speculation on the subject) H,J band brightnesses are not easy measurements to make and amateurs with the capability of measuring in the IR are rare (they use photelectric photometry, essentially a single pixel camera with an IR sensitive photodiode) https://www.aavso.org/infrared-photoelectric-photometry-program AFAIK there was only one commercial instrument for work in the IR and that appears to have been discontinued https://www.optecinc.com/astronomy/catalog/ssp/ssp4.htm

Note also that is possible that Betelgeuse may not actually be dimming at all when all wavelengths are considered as most of the radiation is in the IR and a recent measurements in H,J bands in the AAVSO database appear to show no significant change.

Betelgeuse is one of the MILES standard stars which was recorded in 2000/2001 when the brightness was more typical so you could compare with that (the non deredened version eg in ISIS, filtered to match the Star Analyser resolution.) My spectrum with the ALPY 600 on 30th December 2019 shows only very subtle changes in the visible spectrum compared to then http://www.spectro-aras.com/forum/viewtopic.php?f=38&t=2433#p13514 and there has been no further change up to 9th January. (The later spectrum is with the modified ALPY at R~130 so the typical Star Analyser resolution) http://www.spectro-aras.com/forum/viewtopic.php?f=38&t=2433&start=20#p13584 The spectra are in the BAA database Cheers Robin

You can also tell the type of supernova from the spectrum (Core collapse of a massive star or explosion of a white dwarf which exceeds critical mass)

Here is another spectrum of a type II about 1 month after it exploded (A very early spectrum of mine using a simple diffraction grating mounted directly in front of the camera. ) You can measure the velocity of the explosion from the blue shift in the material coming in our direction (about 8000km/s at this point) http://www.threehillsobservatory.co.uk/astro/spectra_6.htm