robin_astro

The variable star brightness data submitted to the BAA is still held independently in their database but that data is then also periodically uploaded to the AAVSO database. Robin

T200 is the telescope (0.2m aperture). Rotation velocities are quite high so you don't need particularly high resolution. An f4.5 Newtonian is a good choice with the ALPY. A much better match for an ALPY than the slow etx90. 114mm aperture is rather small for objects as faint as this though and exposures are long even with bigger apertures (2 hours in 20min exposures say) so you will need a good mount with good guiding

For exactly edge on galaxies the conversion to a rotation curve is not straightforward though as at any given location, the spectrum is potentially a combination of regions at different radii, each seen with a different component velocity in our direction.

Hi Steve, There are several examples of this measurement by amateurs on the ARAS forum. The observers might still have the spectra. Otherwise perhaps contact the authors of papers where rotation curves measured using optical spectroscopy have been published ? (I think most of them use radio astronomy so you can measure further out than you can do at visible wavelengths) https://www.spectro-aras.com/forum/viewtopic.php?f=6&t=2618 https://www.spectro-aras.com/forum/viewtopic.php?f=6&t=2232 http://www.astrosurf.com/buil/UVEX4/_demo_m82.jpg https://www.spectro-aras.com/forum/viewtopic.php?f=6&t=2420 http://www.spectro-aras.com/forum/viewtopic.php?f=6&t=1682 http://www.astrosurf.com/buil/forum/ngc7331_poster.png Cheers Robin

S&T picked up on our black hole being "on its side" so I did hear right. Apparently this is not unusual with supermassive black holes in the centre of galaxies, with low accretion rates like ours having a wide range of orientations, assumed to be the result of their formation from merged smaller black holes. (Any with jets in the galactic plane must be interesting places to live !) https://skyandtelescope.org/astronomy-news/astronomers-unveil-image-of-the-milky-ways-central-black-hole/?utm_source=cc&utm_medium=newsletter Cheers Robin

I was going by what was said though rather than the appearance in the image. There was also a comment on the jet (if there is one) being difficult to detect as, unlike the one in M87 this would be in the plane of our galaxy. Anyone got a link to the original press conference? I cant find it at the original address Robin

So.. from the press conference I picked up that we see the spinning black hole ~face on (even though we live ~ in the plane of the milky way) and the spin is in the opposite direction to the orbiting accreting material. This seems quite surprising to me. I perhaps naively expected everything to be in the same plane

Yes definitely worth a look with the Star Analyser if you have a deep sky capable setup. The broad Silicon absorption line confirming it as a type 1a is very clear https://stargazerslounge.com/topic/394071-supernova-in-ngc-4647/?do=findComment&comment=4238399 Cheers Robin

If you pop a diffraction grating in front of the camera you can even measure the red shift as here in Patrick Moore's back garden back in 2005 using a prototype of the Star Analyser (bottom of the page) http://www.threehillsobservatory.co.uk/astro/spectra_12.htm Cheers Robin EDIT: You would have to hack the Stellina though. Anyone doing that yet ?

If you have a deep sky capable camera you can take a spectrum of bright supernovae like this just by putting a diffraction grating between the telescope and camera. Here it is with a Star Analyser 100, Atik 314 and CII (18x20 seconds) You can see the supernova (and other stars and galaxies) and the light spread out into the spectrum, blue to red Cheers Robin

Questions welcome, just ask away ! Supernovae are a particular interest of mine. They were once mostly discovered by amateurs as this one was but now most are found by professional survey telescopes. When you discover what is possibly a supernova you then have get it confirmed and determine what type it is by taking a spectrum. (I started doing this in 2016 and have about 40 official classifications to my name now) This one was confirmed officially from a spectrum by Italian amateur Claudio Balcon (just 50 minutes after it was announced) so it is an "all amateur" supernova. Supernovae are exploding stars of course but there are two main types. Some are massive stars which suddenly run out of fuels and collapse under gravity causing the explosion (type II). This one though is a white dwarf in a binary star system which has been grabbing material from its companion until it reached critical mass and exploded like a nuclear fusion bomb. These are the type 1a which are used to measure distances and led to the discovery of dark energy for example Cheers Robin

I love the blue colour, confirmed by the spectrum which is brighter at the blue end Here is the raw spectrum image. (Using an ALPY 600 spectrograph) The deep absorption line marked is from singly ionised Silicon formed by nuclear fusion in the thermonuclear explosion of the white dwarf (this is a type 1a). (The other lines in the background are from natural airglow and light pollution) and here is the calibrated spectrum We can measure the velocity of the material thrown out by the explosion by how far the absorption line has been blue shifted due to the doppler effect (~15000 km/s.) The silicon is actually from the partially "nuclear burned" material near the surface of the white dwarf. Heavier elements up to Iron are produced by further fusion deeper within the explosion. It is near maximum at about mag 12.5 currently which, taking into account the distance to the galaxy makes it several billion time more luminous than the sun Cheers Robin

For stars to test my equipment and processing though I use MILES stars which is a catalogue of stars measured using professional equipment. Here are examples where I have used them with the Star Analyser and the ALPY600 http://www.threehillsobservatory.co.uk/astro/spectroscopy_21.htm (The spectra are as measured ie not corrected for interstellar extinction so what we want) They are included in the ISIS software database but I don't think they are in RSpec. They can be downloaded from the references there though Cheers Robin

Looking more closely at these, I would forget it. They are not particularly good, for example they have made a fundamental mistake of not aligning the grating horizontally which produces artifacts. Also most of the stars are boring and interesting unusual stars for low resolution spectroscopy like Wolf Rayet stars which show up really well with the Star Analyser seem to be missing. A pity because it must have been a massive project

Note though that these appear to be the raw spectrum images, not the calibrated spectra so you haver to process them your self which limits their usefulness

If you want spectra of stars measured using the Star Analyser then this database might be useful. There are thousands of stars there but I have not checked it for quality https://sdc.cab.inta-csic.es/sasdaba/ Also the ELODIE archive which has professional spectra (but at much higher resolution than the Star Analyser) for many stars (A bit of Trivia:- ELODIE was the spectrograph used to detect the first exoplanet 51 Peg b in 1995) http://atlas.obs-hp.fr/elodie/ Cheers Robin

Hi Steve, There are many professional catalogues of spectra but probably the easiest way for "normal" stars is to use Brian skiff's magnum opus "Catalogue of stellar spectral classifications" which has the published spectral types for almost a million stars. http://vizier.u-strasbg.fr/viz-bin/VizieR?-source=B/mk You can then use the classification there to call up the typical spectrum of that type from the Pickles catalogue which is included with several software packages like Visual Spec, RSpec ISIS etc. Cheers Robin

A big chunk of the cost of the ALPY is the guider module (essential) but the 3D printed module used in the Uvex can be used instead with the critical core module part from Shelyak https://spectro-uvex.tech/?p=1820

In the same 3D printed vein, Christian Buil's Starex which can also double as a spectroheliograph in Solex mode (lots of builds of this going on currently supported through forums) http://www.astrosurf.com/solex/sol-ex-stars-en.html Also his Uvex which is a superb wide spectral range all reflective design (now also offered commercially by Shelyak), though it can be tricky to align. https://spectro-uvex.tech/?p=1362&lang=en http://www.astrosurf.com/buil/UVEX_project_us/ Kits of the special optical parts for these are available from Shelyak 3D printed designs do tend to suffer from poorer stability though compared with the very stable ALPY

Correct. the effect of the interstellar medium on the spectrum of distant objects is well defined and different to that seen from cosmological expansion. See Lyman forest for example https://en.wikipedia.org/wiki/Lyman-alpha_forest The animation there is particularly nice Here are some measurements made by me of high redshift distant quasar spectra clearly showing the Lyman Alpha line shifted into the red from the UV and the Lyman forest from absorption by intervening material. The photons forming the rdshifted Lyman alpha emission line are the same ones that left the quasar that were not absorbed/scattered by intervening interactions https://britastro.org/observations/observation.php?id=20210411_134753_85f4b3ebf4faaefe

For fun I thought I would try to take a spectrum of the JWST with my modified ALPY200 faint object spectrograph. (Keeping a mag 14-16 target on the 3 arcsec wide spectrograph slit for 90 mins presents some interesting challenges, also applicable to comet spectroscopy) After correcting for the solar spectrum it turns out that the reflectance spectrum is reddish with a tinge of blue and the green wavelengths significantly attenuated which matches NASA's description of the coatings used on the sun shield. The spectrum and more information are on my BAA webpage here https://britastro.org/observations/observation.php?id=20220327_125654_228ed4b0a22ce097 Cheers Robin

Yes. With slit based systems the resolution is fixed by the slit width but with slitless systems it will depend on the star image size (seeing etc) Cheers Robin

1) To measure the resolution you need a spectrum line which is narrow compared with the resolution of the spectrograph. With slit spectrographs this is usually measured from the width of one of the calibration lamp lines. with a slitless spectrograph you can measure it from a line in the star spectrum you know to be narrow. You can see an example here where I used the lines in P Cygni. http://www.threehillsobservatory.co.uk/astro/spectroscopy_16.htm#SA200_filter_wheel You will often see the resolution quoted as resolving power R = wavelength/resolution so for example an R of say 120 typical of a simple Star Analyser setup equates to a resolution of 50A at 6000A while my LHIRES at maximum resolution has a resolving power of ~15000 or 0.4A 2) Be stars are main sequence B stars which intermittently show H alpha in emission, from a circumstellar disc. They are a popular amateur target as they are part of a big pro am project to track them and better understand how the disc forms and disappears. There is a database dedicated to them http://basebe.obspm.fr/basebe/ and a website which shows which stars need spectra currently http://arasbeam.free.fr/?lang=en Be Candidates are stars which have been found with Be like emission but are not currently catalogued as such. (Because discs form and disappear a normal B star can turn into a Be star) There was an amateur systematic survey to discover some of these a few years back http://www.astrosurf.com/aras/be_candidate/auto-be-candidate.html and candidates pop up from time to time for example in the Gaia transient survey where they can be followed up by amateurs eg https://www.spectro-aras.com/forum/viewtopic.php?f=40&t=2940 Another popular area of pro-am work is Cataclysmic variables. (novae, dwarf novae, symbiotic stars etc) There are more examples in the ARAS database https://aras-database.github.io/database/index.html Cheers Robin

You could perhaps take look in the BAA database to see what others have been looking at for a particular time of year. (Most observers there are northern hemisphere, though accessibility will still be latitude dependent of course ). They are generally at higher resolution than the typical Star Analyser spectra (you can limit the resolution in the search if you like) but you should be able to see the main features shown there provided they are bright enough for your setup https://britastro.org/specdb/data.php (enter the date range of interest) Cheers Robin

What a bizarre and alarming incident. Strangely not the first telescope to be attacked though. https://astroanecdotes.com/2015/03/26/the-mcdonald-gun-shooting-incident/