robin_astro

Supernova spectroscopy is a particular interest of mine. Most supernovae are very faint even at maximum so I am one of only a couple of amateurs who confirm and classify supernovae spectroscopically using a spectorgraph I specially modified for the job. http://www.threehillsobservatory.co.uk/astro/spectroscopy_20.htm The spectrum changes quite rapidly in the first few days/months, mainly due to the hot material cooling (shifting from blue to red over all) and becoming more diffuse (giving a spectrum with strong emission lines like a nebula) . You also see different lines appearing as the new elements produced decay. Most SN are too faint to be followed very long spectroscopically by amateurs but it is possible with the brightest ones. Here is one (a type II like Betelgeuse will become) which I followed for a year from mag 13 to mag 18 (from from a BAA presentation I gave) Cheers Robin

There would still be much of interest from a spectroscopic point of view though and something that bright would give professionals a big headache. Even with my equipment I am not sure how I would cope. I would probably have to resort to defocusing and sampling the defocused image using the spectrograph slit as I did for Vega with this simple setup here for example http://www.threehillsobservatory.co.uk/astro/spectroscopy_18.htm (Off topic in this sub forum though)

Not likely to be a problem for the secondary as the light (and heat) is unfocussed at that point and being a mirror, most of the light and heat is reflected. But once focused then a source as bright as the moon concentrated from a telescope of signifcant aperture onto a few pixels (or on the retina) would be something to avoid

Supernovae put out a lot of light though (Around a billion or so times more luminous than the sun at visible wavelengths) so yes, around the brightness of the full moon by the time it gets here. Something with the apparent size of a star in the sky producing as much light as the full moon will be painfully bright.

SN 1987A (another type II but a very different progenitor) was ~0.1-0.2 arcsec apparent diameter after 3.5 years according to this Hubble image https://hubblesite.org/image/20 which given the ~300x difference in distance would suggest the Betelgeuse remnant would be perhaps Jupiter size in the same timescale?. SN 1987A was made more interesting because is also lit up a ring of previously shed circumstellar material but I am not sure if there is much of that from Betelgeuse. (SN 1987A was a blue supergiant)

That will be mainly high energy (gamma to UV) though initially. We have to wait for it to cool a bit and for the energy from the decay of newly formed unstable elements to be generated to see the maximum in the visible light.

The first evidence of it having gone supernova will be from a burst of neutrinos from the initial core collapse, some hours before the shock wave breaks though the outer surface of the star and we see the first light from the explosion

But as Ouroboros pointed out it will be a week or two before it reaches maximum brightness in visible light so there is no danger of being unexpectedly accidentally blinded

Those are brightnesses integrated over the area of the object though. The light from Betelegeuse as a supernova will be concentrated as a stellar point source. For a telescope in typical seeing that would be about 300,000 times smaller in area than the sun or moon (equivalent to around 14 magnitudes) so the surface brightness of Betelgeuse when viewed through a telescope could indeed rival that of the sun so would certainly be dangerous and potentially with the naked eye too, though type II supernova are a mixed bunch with a big spread in maximum luminosity. Cheers Robin

Take care though. The spectra of most stars are not black bodies and the effective temperature Teff normally quoted for a star is the temperature of a black body with the same total luminosity which for A stars is very different from a best fit Planck curve to the visible part of the spectrum eg from Wikipedia where Teff is 9500K but the best fit curve is 15000K

ISTR this is a fast f4 telescope hence the recommendation for the SA100 provided it would fit. Having to rotate the spectrum to horizontal in software is not ideal, particularly for colour cameras but as you have a mono camera you can get away with this. (Most of my work with the Star Analyser has been done with the spectrum at odd angles!) If you do see rotation artifacts make sure you get even coverage of pixels by taking several subs and allow some drift or dither a bit between them, then align and stack. Yes the LP filter will leave holes ! eg http://www.threehillsobservatory.co.uk/astro/filter_spectra_3.htm Cheers Robin

Very true. (In the DN Tau event the excess flux was effectively a good match to a black body curve with no obvious features.) Cheers Robin

Qualitatively remarkably similar to the DN Tau event but perhaps rather hotter looking at difference in the spectra between quiescence and maximum http://www.threehillsobservatory.co.uk/astro/spectra_42a.htm Cheers Robin

Fantastic ! Good to see the system up and running. A 50% increase in flux in what, a couple of minutes? You would not want to be living on an exoplanet round that star. Cheers Robin

Checking in the extrasolar planets encyclopedia http://exoplanet.eu/catalog/ I see there are currently 23 exoplanets with known mass less than 1.5 earth. Almost all were discovered using the transit method. How were the masses of these planets determined? Using ESPRESSO as a survey instrument sounds very inefficient compared with transit surveys. Is there a science program planned using ESPRESSO as a survey instrument or is its main task following up known transiting exoplanets ? Wikipedia suggests that ESPRESSO is currently not doing much better than HARPS 30cm/s precision. Do you have any inside information on the latest status ? Cheers Robin

😁 Thanks !

I thought I would share the discovery of this dwarf nova as nice example of international amateur cooperation On 2019-11-30 Simone Leonini , a member of the amateur Italian Supernova Search Project, http://italiansupernovae.org/ discovered a supernova candidate at mag 16.5 close to the galaxy UGC11775 in Cygnus. This was posted on the IAU Transient Name Server, the official site used by both amateurs and professionals for posting possible supernova discoveries. https://wis-tns.weizmann.ac.il/object/2019vww I monitor TNS as I can potentially confirm supernovae spectroscopically provided they are bright enough using a specially modified ALPY spectrograph http://www.threehillsobservatory.co.uk/astro/spectroscopy_20.htm . I recorded a spectrum of the object, designated AT 2019vww the following evening. The spectrum (seen on the TNS site) showed clear hydrogen alpha emission but the red shift was zero rather than the expected 0.016 for the nearby galaxy so likely to be a Cataclysmic Variable (a nova or dwarf nova) in our galaxy, though the signal/noise in the spectrum of this faint object and the resolution of my instrument, designed specifically for supernovae was not sufficient to determine the exact nature. An Astronomical Telegram was issued on 2019-12-11 announcing the discovery. http://www.astronomerstelegram.org/?read=13345 The centre for Backyard Astronomy are an international group of amateurs who observe CV outbursts using high cadence, high precision photometry. Tonny Vanmunster, based in Belgium is a member of CBA and author of Peranso software used to analyse these variations. http://www.cbabelgium.com/ He observed AT 2019vww over several nights and has announced the discovery of superhumps, short period regular variations in brightness, confirming it as a new SU UMa type dwarf nova. http://ooruri.kusastro.kyoto-u.ac.jp/mailarchive/vsnet-alert/23781 Monitoring of AT 2019vww continues and it has been added to VSX, the AAVSO database of variable stars https://www.aavso.org/vsx/index.php?view=detail.top&oid=1499962 Robin

Looking good ! Since Castor is a double and you have the two stars aligned in the dispersion direction there is likely to be some blurring due to the overlap of the two spectra. If you orientate the camera plus grating so the two stars are one above the other, you could probably split the two spectra to show that they are very similar spectroscopically. Other interesting targets to try comparing are delta Cas and gamma Cas. Both are hot main sequence stars but the emission from the disc round gamma Cas turns H alpha and beta into bright emission lines Cheers Robin

Interesting test target. For fun I dug out some B,V light curves from this paper https://academic.oup.com/pasj/article/62/2/457/1461174 and plotted a rough B-V curve. There is a bit of scatter, probably because the B ,V measurement times were not coincident, but there is about a 6-7% colour change. Not the primary purpose of course but I wondered if that is large enough to pick up in your spectra ? Cheers Robin

Yes it is important with glass mirror slits that the reflective coated surface is towards the spectrograph (ie they are back coated like a domestic mirror, not front coated like usual astronomical mirrors.) If you use them the other way round with the reflective surface towards the telescope, some of the light that passes through the slit gets reflected off the back off the internal glass surface, then off the internal side of the reflective surface and back into the spectrograph producing a ghost spectrum. (The right way round, you do get a faint ghost image in the guider but this is not a problem) Robin

Yep the aim is to have one square km of signal collecting area eventually. Including all the proposed sub arrays, the effective aperture would be 3000km. [ 20% of total collecting area will be within 1 km diameter [ 50% of total collecting area will be within 5 km diameter [ 75% of total collecting area will be within 150 km diameter [ Maximum baselines will be at least 3,000 km from array core. From https://www.skateles...rochure_web.pdf though the date of that brochure predates the decision to build arrays in both Africa and Australia. AFAIK nothing has been built yet though (or even funded?) apart from the headquarters building at Jodrell Bank Robin

The faster the optics the better they need to be. That is why stopping down the lowspec (or using a higher f ratio telescope) gives better results with the simple achromatic doublets used there. Dont forget to allow for the fact that the grating is at an angle when choosing the size to avoid vignetting (eg at high resolution where the angle get large, the LHIRES III uses a 25X50mm grating. Compact designs with lightweight components ( ie high dispersion grating, small diameter short focal length lenses, the ALPY is an extreme example ) are easier to make mechanically rigid than using long focal lengths. Even a few microns movement is significant and can degrade the spectrum resolution in long exposures. Robin

The old Olympus SLR lenses are pretty good and can be picked up at a reasonable price eg as used here with an eyepiece as collimator http://www.threehillsobservatory.co.uk/astro/spectroscopy_19.htm or here in an objective grating setup http://www.threehillsobservatory.co.uk/astro/spectroscopy_17.htm

PH make the gratings that Jeulin sell You could make a TRAGOS using the Star Analyser 200. http://www.burwitz-astro.de/spectrographs/tragos/index.html or an ALPY copy using the 600l/mm grism from the PH DV spectrograph. (Not as good though as the ALPY uses special optics with reduced chromatism) Robin

Nope, they are 600 l/mm grisms. Two different diameters in the two versions. I think the one in Fulivo's "ALPY/TRAGOS copy" is the larger size Robin