robin_astro

It was withdrawn on TNS on Saturday within a few hours of its "discovery".   It is labelled as "unconfirmed" in David Bishop's "rochester" page meaning that someone has looked there and not found anything

Even if it had existed it would have been too bright for any normal supernova at maximum at the distance of the suggested galaxy so would likely have been a transient object in our own galaxy (nova, dwarf nova, luminous blue variable etc etc) but since it does not exist that is hypothetical  The correct procedure for reporting transients is to make a follow up observation first and check for any other possible sources eg asteroids etc. Only then should a discovery claim be made either through TNS or via the IAU transient object page

http://www.cbat.eps.harvard.edu/unconf/tocp.html

1 hour ago, Malpi12 said:

 

eeek aavso is telling me AT2023mlt "Star AT2023mlt does not exist in VSX"  what am I doing wrong I wonder ?

Even if it had been a transient (it is only a supernova once confirmed by spectroscopy, it would only exist in VSX after somemone added it.  TNS (Transient Name server) is the definitive place to look for possible and confirmed supernovae

 https://www.wis-tns.org/

Robin 

it is a false alarm and does not exist

https://www.wis-tns.org/object/2023mlt

Robin

5 minutes ago, robin_astro said:

I am not sure but I think there is a setting somewhere which allows several short exposures to be averaged (or some kind of filtering of corrections perhaps?)

Yes it is the Z filter algorithm. I have not used it before but I might investigate it the next time I see this kind of problem

Cheers

Robin

Yes I see the same issue of loss of lock where the star is overexposed. I am not sure but I think there is a setting somewhere which allows several short exposures to be averaged (or some kind of filtering of corrections perhaps?)

Cheers

Robin

It is more common to mount them in a circle to give even illumination independent of  the orientation relative to the direction of the slit.  A nice setup suggested by Christian Buil with his StarEx  is to feed optical fibres to small clips round the edge. The obstruction is small and they can be left mounted without significantly disturbing the telescope throughput. They can even be switched on during the exposure to superimpose lines on the spectra giving very high precision calibration for example where flexure might be an issue during long exposures.

https://groups.io/g/Solex-project/topic/88905429

(In French but the photos tell  the story and Google etc translates well if you need more information)

Cheers

Robin

There is a excellent piece on this supernova in the "Science in Action" radio programme on the BBC World Service. Astronomers , both amateur and professional tanking enthusiastically about the discovery and what they know about it so far.  Some great Science and even a live observing session on the radio 🙂

https://www.bbc.co.uk/sounds/play/w3ct4sc9

They talk about the way the early spectroscopy shows the interaction of the explosion with the surrounding circumstellar material. Here is an animation of  my measurements showing that early interaction during the first week

Cheers

Robin

1 hour ago, SteveBz said:

I calculated the R number. The half height width for Ha seems to be about 0.16 so R=656/0.16 or about 4000. Is that right?

Provided the actual width of the line is significantly narrower than the resolution then yes this works but Ha alpha can be wide particularly in some stars eg like in Vega so you really need a line which is known to be very narrow. Try measuring the width in some of the narrow metal lines in your spectrum and see if this gives a higher resolution or  sky lines (natural or from light pollution) or from narrow lines in the calibration lamp provided it illuminates the spectrograph well (Note a single small lamp at the telescope aperture will not work for this as it like  a very high focal ratio pinhole camera and gives a perfect in focus image even when you are out of focus! If doing this using neons arrange 3 or 4 of them round the aperture edge)

Cheers

Robin

If you are looking specifically around H alpha at high resolution a simple neon lamp will do the job. Point the telescope at a bright A or B star and look for H alpha which will be obvious as there will be no other strong lines near it. Then when you have it centred take a neon lamp as a refence and identify the lines from for example Christian Buil's website here

http://www.astrosurf.com/buil/us/spe2/hresol4.htm

Cheers

Robin

38 minutes ago, Jeff C said:

Coincidentally I imaged M101 on thursday night pre-supernova, so I conveniently had data from just about 24 hours before the event

The supernova is clearly there in your first image. It was discovered on Friday ~17:00 UTC but there are pre discovery images found so far which show it back to Thursday evening (UTC) see

https://www.wis-tns.org/astronotes/astronote/2023-125

Apologies if I have already asked you about this image on Cloudy Nights (I get confused with the different names) but what is the date and time on the first image ?

(These images are potentially important scientifically to constrain the exact time of  the explosion)

Thanks

Robin

On TNS currently   

latest non detection  2023-05-18 10:17:15 (UTC)  (ATLAS)

earliest detection      2023-05-19 03:41:35 (UTC)  (Stephen Limeburner)

https://www.wis-tns.org/object/2023ixf

The gap is closing ! Can anyone narrow the time of explosion down further ?

Robin

1 hour ago, ONIKKINEN said:

One of those blobs maybe?

Looking at Nick James' image on the BAA forum I would say it is located in the blank space in the middle of  that horseshoe of stars

https://britastro.org/forums/topic/supernova-in-m101#post-617411

Cheers

Robin

Latest measurement  2023 May 20.4517UT  by Robert Fidrich on VSNet-alert puts it already  at mag 13.  Being a type II, it probably wont get as bright as type 1a 2011fe in M101 did though which reached mag 10

Cheers

Robin

ZTF report a 10 hours pre-discovery detection at mag 15.9 (g) 2023-05-19 07:45:07 and a negative (fainter than 21.3) 2023-5-16 19:35:38.00
https://www.wis-tns.org/astronotes/astronote/2023-120

so any deep images taken between those dates could be of interest

Here is a link to the discovery image

Cheers

Robin

Koichi Itagaki has discovered a supernova  in M101 tonight. 

https://www.wis-tns.org/object/2023ixf

mag 14.9 at discovery, it has  been confirmed and classified spectroscopically as SN 2023ixf, a type II (core collapse) supernova

Robin

28 minutes ago, gort said:

 Consider an excited H atom and a transition from n=3 to n=2. That transition will emit a single photon in the red (656nm) and energy 1.89eV. 

The photons  have this energy on average but individual photons will have a spread of energy values even for photons repeatedly emitted from a single isolated atom, dependent on the lifetime of the excited state such that ∆E∆t ≈ h/2π. This is seen observationally as a broadening of the spectral line.  This is an example of the fundamental uncertainty inherent in our quantum world.

Robin

51 minutes ago, SteveBz said:

Can I ask, how do you find ta specific star?  Are you able to plate-solve in the guide-scope?

I am quite old school.  My scope is linked to Cartes du Ciel. I use the finder (with a webcam strapped to the eyepiece) to find  bright stars and then centre  them in the spectrograph mirror slit guider (I don't have a guidescope on the telescope) and align on them. I then star hop to the target using fainter stars using CdC and the guider image, syncing as necessary as I go . For crowded fields I download and overlay a DSS image to CdC so I can match what I see in the spectrograph guider and identify the target. (I usually then take a shot of the guider image as a record that I took the right target) Very occasionally If I get completely lost I may resort to taking a deeper guider image and plate solving it but that is rare. 

Cheers

Robin

12 minutes ago, SteveBz said:

Did you take this with a colour camera, or add the colour afterwards?

This was taken in colour with a Toucam pro  webcam and 85 frames stitched to together. The first spectrum I took with my newly constructed LHIRES kit back in 2006. 

Here is a recent much better one by Olivier Masse 

https://oliviermasse.fr/solex/20230502_solex_spectre_complet_5000.png

from this thread on the Solex forum

https://groups.io/g/Solex-project/topic/colorisation_spectre_complet/98665300

Here is mine with a LHIRES (much reduced) Unfortunately I lost the full size version.

http://www.threehillsobservatory.co.uk/astro/spectra_28.htm

I suggest moving to the red until you see the very distinct Oxygen telluric band pattern (at the end of my spectrum) and then work back from there.  H alpha is broad and strong, the Na D lines are distinct but some of the weaker lines round there are telluric water lines so dont always show clearly. The Mg triplet should also be clear. At the violet end you should see two broad strong Calcium H J lines before the sensitivity of the camera runs out

Cheers

Robin

22 hours ago, gort said:

For a single photon, we can compute its energy, hence, its momentum, quite easily.

You can compute the theoretical energy but if you measure it  you find a spread of values. This is seen for example  in the natural broadening of spectral lines. The lines from transitions with a short lifetime are broader in agreement with HUP

Cheers

Robin

Here are some examples just posted on the solex/starex  forum of some spectra at both high and low resolution with a StarEx and an f5 Newtonian so quite demanding for the spectrograph optics. The results look good even down to  below 3800A in the UV and up to 9500A in the IR

https://groups.io/g/Solex-project/topic/un_session_au_newton_200f5/98516943

Robin

2 hours ago, CharlieM said:

If a single lens is going to be so much of a problem, perhaps I need to look at the UVEX as opposed to the StarEx, which was my plan forward ??

If you are relatively new to spectroscopy and are looking for a home build I would go for the StarEx. The optical kit for it from Shelyak uses specially designed lenses which perform better in the blue than standard off the shelf achromats and it is a good match for the f8 RC8. The UVEX is more an advanced design for experienced observers, particularly if looking for the best performance in the UV but it  is tricky to get working well.  

Cheers

Robin

8 hours ago, CharlieM said:

I hope you don't mind the newbie questions but I notice on that page that Christian is using a lot more lenses than i have seen in the DIY designs like the Starex

That is a good and interesting question.  This was one of his earliest spectrograph designs and in that case he just used standard SLR camera lenses which have many elements to correct for various aberrations, important for making good sharp images across the field at low focal ratios rather than specifically for spectroscopy. You can use simpler (smaller and lighter) achromats in spectrographs eg the StarEx, LowSpec, LHIRES all use achromats but they do have drawbacks such as not working well at low focal ratios and suffer from chromatic aberration, particularly noticeable as a shift of focus at the blue end of the spectrum. The ALPY also uses achromats and works well down to f4 but they are specially designed lenses that Christian designed to minimise chromatism in the particular application.  There are commercial designs that use multi-element camera lenses like Shelyak's LISA and eShel (A good sharp image over a wide field is particularly important in echelle spectrograph designs) but even there chromatism at the blue end can be problem even with high quality camera lenses. Spectroscopy is a severe test for chromatism and most professional spectrographs use all reflective optics. Shelyak's UVEX is an example of this but they are difficult to design and align to be free of other aberrations.

Cheers

Robin