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robin_astro

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About robin_astro

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  1. The direct link to the series of articles (in English) is here https://astropeiler.de/beobachtungen-der-21-cm-linie-mit-einfachen-mitteln Robin
  2. You could build a "Micro Arecibo" using your satellite dish (fig 14 of the pdf)
  3. I was surprised to find that given a decent receiver lineup the Milky Way Hydrogen line is detectable with some remarkably simple antennae (eg even a dipole plus a CD as a reflector !) https://astropeiler.de/sites/default/files/Hydrogen_4.pdf From this website https://astropeiler.de/
  4. ALPY is fixed resolution at ~12 Angstrom. (Except for my modified supernova classifier version ) . You can vary the dispersion/resolution of the Lowspec by changing gratings and slit width. There is a lot more to a spectrograph than this though. For example the ALPY is designed to operate down to f4 whereas the Lowspec has severe chromatism at low f ratios due to the simpler off the shelf optics which means the spectrum goes out of focus at the blue and red end. To avoid this you need to run a higher focal ratio which means a wider slit and a higher dispersion for the same resolution. The ALPY is also extremely stable both with regards to temperature and flexure and so once set can be run without any intervention, good for remote operation. Of course you also need to produce the parts and assemble them with the Lowspec. (A commercially produced Lowspec would likely be more expensive than the ALPY, similar to what happened with the LHIRES which was originally a not for profit kit ) Theclosest commerical comparison with the Lowspec is probably the Shelyak LHIRES or Baader DADOS Cheers Robin
  5. The manuals which go with the Star Analyser and ALPY also have some useful general information on how to record and process spectra https://www.patonhawksley.com/resources https://www.shelyak.com/produit/alpy-600/?lang=en
  6. Also the spectroscopy resources page on the BAA website https://britastro.org/node/19378 For example my NLO workshop presentations which cover producing spectra using both the simple slitless Star Analyser grating and an ALPY 600 slit spectrograph https://www.britastro.org/downloads/15701
  7. Yes. The larger the aperture the more photons you collect in a given time. (You might decide to spread them over the detector to a different extent eg by choosing the focal ratio but that is independent of aperture). The more photons you collect the more you know about the object as I demonstrated up the thread so the larger the aperture and the longer you "stare" at it, the more information about the object you acquire. In a perfect system (no noise, no distortion of the signal between the object and you) :- The first photon tells you there is an object emitting light the second photon (or more accurately, the time between them and the difference in direction) tells you a little bit more about the object (A hint towards deciding if it is a point or an extended source and very, very roughly its brightness) The third and subsequent photons increases the precision of the brightness estimate and if it is an extended object adds information about the size, structure and brightness variation across it. Each subsequent photon adds more detail in the way I described. Different equipment may have different abilities to distinguish which direction they are coming from (spacial resolution) but at the end of the day the more photons, the more accurate description of the object you get Robin
  8. 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
  9. 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. .
  10. 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 ? )
  11. 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
  12. 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
  13. Should be some first-hand accounts of 1987A eg an account of the discovery retold here http://www.oasi.org.uk/Misc/SN1987A.php
  14. 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
  15. 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
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