robin_astro

Having a related problem doing spectroscopy tonight. The H alpha emission is so intense that the raw signal at H alpha is now something like 3000x greater than that in the continuum in the violet. I am having to take big stacks of short(ish) exposures to get a vaguely decent signal/noise in the violet while avoiding saturating at H alpha Robin

It has managed to garner an impressive amount of rotational energy though which (may) power the relativistic jet. As the authors of this paper https://arxiv.org/abs/1904.07923 put it "This enormous amount of energy trapped in the black hole rotation implies a rotational energy of about 10^64 erg, comparable to the energy emitted by the brightest quasars over billion year timescales"

Not as close in as the famous image of course but you can observe the light from the material orbiting the black hole with a relatively simple spectrograph as here on my BAA page https://britastro.org/observations/observation.php?id=20190411_213200_531d1ec6d134b3dc Cheers Robin

I remember in 2006 visually it looked straw coloured a few days after outburst turning to very red over about 2 weeks. The change might not be so obvious in a DSLR image though depending on the sensitivity to H alpha

The sensor is only one part of the overall response though. The grating response is as important and also has a similar shape. Coatings on the optics and the atmosphere also have an effect and if you are using a slit spectrograph the defocussing effects of any chromatism (including atmospheric dispersion) can affect the fraction of the light going through the slit depending on the wavelength. The trick to dealing with all these factors though is to measure a star with a known spectrum and use this to flux calibrate the unknown. There is a document on my website which covers how I do this which you might find useful. http://www.threehillsobservatory.co.uk/astro/spectroscopy_21.htm Cheers Robin

These are Fe II, commonly seen in Nova spectra Cheers Robin

This paper describing the changes in the spectrum during the 2006 outburst is a good reference to compare with. https://academic.oup.com/mnras/article/474/3/4211/4768437 fig 1 which covers the first week is relevant at the moment and identifies the main lines in the spectrum (H ,Fe II, Ca II) Cheers Robin

This is mainly due to the response of the instrument which is less sensitive at H alpha compared with H beta. To compare intensities of emission lines at different wavelengths you first need to subtract the background and correct for the response of the instrument and atmospheric extinction (which is quite high for RS Oph here in the UK due to the low altitude) using a standard star. Flattening the spectrum (rectifying it) allows you to compare the strength of absorption lines as they are a proportion of the total continuum but it distorts the differences in the relative strength of emission lines) Here is a spectrum corrected for instrument and atmosphere (calibrated in relative flux) from tonight using the ALPY 600. Cheers Robin

Do you mean viewing visually through a spectroscope ? While it is bright enough I would say quite possibly at low resolution but as it fades you would need a big telescope to view the spectrum visually as the light is so spread out by the spectrograph. This is what the spectrum looked like tonight in a 30 second exposure at low resolution with an ALPY600 spectrograph The spectrum covers the near UV (~3700 Angstrom) to the near IR (~7900 Angstrom) The bright spot right of centre is the H alpha emission. This is expected to increasingly dominate the spectrum in the days ahead turning the star from its current straw colour to a deep red visually Cheers Robin

That tallies with my notes from the 2006 outburst accompanying my Star Analyser spectra which described it as straw coloured a few days after outburst. If it follows the same trend as then it should change to a deep red over the next week or so as the H alpha emission comes to completely dominate the spectrum. Over on CN Keith Geary describes it as blue when he discovered it in outburst, now pale yellow last night and George Wallerstein describes it as purple initially at the outburst in 1958 in this interesting S&T article from 2005 published just before the 2006 outburst https://skyandtelescope.org/observing/celestial-objects-to-watch/when-will-rs-ophiuchi-next-blow-its-stack/

https://stargazerslounge.com/topic/381251-eruption-of-the-recurrent-nova-rs-oph/ A must see target if you have a Star Analyser (or any spectrograph) Here are my observations from the 2006 outburst. I expect there will be a lot more spectroscopic interest this time round http://www.threehillsobservatory.co.uk/astro/spectra_24.htm Cheers Robin

A must see target if you have a Star Analyser (or any spectrograph) Here are my observations from the 2006 outburst http://www.threehillsobservatory.co.uk/astro/spectra_24.htm Cheers Robin

Spectra from the last two night with some emission lines identified (The earliest predates the one described in the ATel by 4 hours) Cheers Robin

small Newtonians are the ideal scope to with the Star Analyser. As my calculator on the RSpec website shows f4 is at the fast end but still just ok for an SA100. Cheers Robin

A spectrum from last night. We can see from this why the Nova looks so red, particularly in images. By digitally filtering the full spectrum (Blue) by multiplying it by the response of a photometric V filter (Pink) we can see the light that would pass through the V filter (Green). If we measure the area under the green curve and compare it with the area of the H alpha line (between the two dotted lines) we find that there is over twice as much light in just the H alpha line compared with all the light passing through the V filter. Cheers Robin

The BAA also offer a mentoring service for members looking to bring their spectroscopy up to research standard for inclusion in the BAA spectroscopy database The BAA spectroscopy resources page can be found here https://britastro.org/node/19378 Robin

For anyone specifically interested in the details of amateur spectroscopy of Novae and possibly contributing, the ARAS forum have followed several in international collaboration with professionals. Nova Del 2013 was the first major example http://www.astrosurf.com/aras/novae/Nova2013Del.html and the current threads monitoring Nova Cas 2021 and Nova Her 2021 can be found here https://www.spectro-aras.com/forum/viewforum.php?f=36 Cheers Robin

Looks good. Here are spectra by Hugh Allen and David Boyd at around the same time from the BAA spectroscopy database https://britastro.org/specdb/data_graph.php?obs_id=9977%2C9978&multi=yes&mix_flux=yes There are two clear broad lines with P Cygni profiles. H alpha with emission at 6563A and another line with emission at ~6350A (Si II ?) both with absorption at about 80A /3700km/s to the blue (P Cygni shape profiles) The features to the red of H alpha are mainly telluric absorption bands from O2 and H2O in our atmosphere (Note the dramatic change just 2 days later in my spectrum up the thread) Cheers Robin

Good question but its complicated and above my level of expertise so I will hand you over to Prof Steve Shore who did a running commentary of the evolution of the spectrum of Nova Del 2013 based on amateur spectra http://www.astrosurf.com/aras/novae/Nova2013Del.html Here is my spectrum from last night with the Hydrogen lines marked (It is not poor resolution. The lines really are that wide !) This is the H alpha line profile plotted in velocity space. The velocities at the edge of the line are ~+-4500 km/s, very high for a Nova (almost Supernova territory, though this is a very different process. In a type Ia supernova the whole white dwarf explodes. Here only a thin shell of material (that has built up on the surface of the white dwarf from the companion star) has detonated. The w shaped wiggles on the top of the line profile contain information about the 3D shape of the explosion. (I think it may mean it was a bipolar shape but don't quote me !) Cheers Robin EDIT: We are seeing the full range of +- velocities in the emission line profiles both towards and away from us now so I guess the ejecta must optically thin (transparent) now

Yep that's right. P Cygni is a Luminous Blue Variable, a hot supergiant star which produces powerful stellar winds which glow in H alpha. Here is an example of its H alpha line by John Foster from the BAA database https://britastro.org/specdb/data_graph.php?obs_id=6544 This is a similar (though temporary and much more powerful) situation. We see the glow directly from the material thrown out sideways by the explosion which produces an emission line. The material coming directly towards us though is lit from behind so we see an absorption line. This is blue shifted by the doppler effect so we see the combination of an emission line and a blue shifted absorption line - the P Cygni line profile. Here they are in Hugh Allen's spectrum of the nova for example https://britastro.org/specdb/data_graph.php?obs_id=9977 but in my spectrum last night the emission now completely dominates and we no longer see the P Cygni profiles shape. (I'll post the processed spectrum later) Cheers Robin

The spectrum was pretty featureless at first but soon developed P Cygni lines and then quickly moved to just strong broad emission lines. It is very striking looking at it tonight. Here is a 10 min raw spectrum image using the ALPY600. The very bright blob is H alpha Cheers Robin

These spectra were recorded using my specially modified ALPY200 faint object spectrograph. My spectra are in red overlaid on spectra from the literature in grey. The main peak is the Lyman alpha line, normally in the UV at 1216 Angstrom but here cosmologically redshifted into the red region of the visible spectrum. (The light travel time is over 12 billion years) More details on this page on the BAA website https://britastro.org/observations/observation.php?id=20210411_134753_85f4b3ebf4faaefe Cheers Robin

Only indirectly on topic for this thread but for a dose scientifically rigorous but distinctly outside the box thinking I periodically dive into exoplanet astronomer Prof Greg Laughlin's fascinating blog https://oklo.org/ The latest talks about "grabby" civilisations which grab a sphere of influence and how it is all described in Depeche Mode's "Everything Counts"

As I understand it, even if you did take one of the pair with you on your intergalactic journey, you could not use it for communication when you arrive as you cannot chose the state when you "open the box"

Hi Jeremy You can use a model of the atmospheric extinction and depending on the accuracy you are looking it you might find a single set of coefficients (or seasonal ones) good enough http://astrosurf.com/aras/extinction/calcul.htm or measure the extinction directly using stellar measurements at different elevations (either the same star as it rises or different stars with known spectra) You do need stable conditions for the period of the measurements though.. You end up with something like this http://www.astrosurf.com/buil/atmosphere/transmission.htm Cheers Robin