18 replies to this topic

[robin_astro]

SN 2022hrs at mag 13 in NGC4647 is looking a nice target tonight in the ALPY 600 spectrograph

 

Here it is on the slit in the guider image (15 seconds exposure)

 

 

and a quick raw image of the spectrum (stack of 4x600sec exposures)

 

 

The deep broad Silicon absorption band at 6335A rest wavelength is obvious indicating it is a type 1a, an exploded white dwarf in a binary system,the silicon having been produced in the nuclear explosion

 

Cheers

Robin

[Organic Astrochemist]

Great spectrum Robin, thanks for sharing.

Just the other day Professor Steve Shore was trying to explain to a group of us how a nuclear bomb explosion would look very different in space than on earth. And here you are looking at one.

You show the Si II absorption, but just what light is that silicon absorbing? If I understand correctly, the carbon-oxygen rich, hydrogen-helium poor white dwarf exceeds the Chandrasekhar limit undergoes runaway nuclear reactions that synthesize heavier elements and release so much energy that they blow apart the white dwarf.

So the light comes from the ejecta because the white dwarf is gone? First decay of newly synthesized Ni-56 and then Co-55 provide the energy around a shortly after maximum light, but I suspect that the explosion and these decays don’t release primarily in the visible spectrum. So the higher energy has to be reprocessed to longer wavelengths and released from regions with lower optical depth.

So the light and the absorption that you have shown us comes from the outer part of the ejecta from a former C/O white dwarf? Is that about right?

[robin_astro]

So the light and the absorption that you have shown us comes from the outer part of the ejecta from a former C/O white dwarf? Is that about right?

I guess so, sort of like a  large rapidly expanding star where the radiation from the hot inner part of the explosion is reprocessed to lower temperatures and the cooler Si rich outer region is equivalent to the photosphere. (Silicon is produced in the incompletely burned outer region while heavier elements  are produced in the denser inner region.) It is important to note though that we still don't actually know what systems  produce type Ia supernova conditions (accretion onto a white dwarf from a companion normal star or a merger of two white dwarfs or both ?)

 

Anyway here is the processed spectrum in black overlaid on a template type Ia from SNID in red

 

[robin_astro]

There's a review paper here but that is 10 years old now and I'm not sure what progress has been made since  then

https://www.nature.c.../ncomms1344.pdf

 

Cheers

Robin

[robin_astro]

This is how it looks with the Star Analyser tonight 

SA100 with the C11 and ATIK314 at 15 A/pixel  18x20sec

 

Cheers

Robin

 

[Organic Astrochemist]

I guess so, sort of like a  large rapidly expanding star where the radiation from the hot inner part of the explosion is reprocessed to lower temperatures and the cooler Si rich outer region is equivalent to the photosphere. (Silicon is produced in the incompletely burned outer region while heavier elements  are produced in the denser inner region.) It is important to note though that we still don't actually know what systems  produce type Ia supernova conditions (accretion onto a white dwarf from a companion normal star or a merger of two white dwarfs or both ?)

 

Anyway here is the processed spectrum in black overlaid on a template type Ia from SNID in red

 

sn2022hrs_20220422_snidfit.png

Thanks Robin,

At least I don't feel so badly about being intimidated by these strange spectra. Here's a quote from Cecilia Payne-Gaposchkin

"With the testimony apparently so conflicting, it is difficult to form any conception of the class of this spectrum"

From A review of type Ia supernova spectra

 

It's interesting to me that one obvious difference between your spectrum and the template is the blueshift of the Si II and Ca II H&K blend absorption (3600−3900 A). The paper by Parent suggests that "The spectra of many SN Ia have shown evidence for high-velocity absorption lines of the Ca II NIR triplet", which would be consistent with fast-moving Ca II. Why is this present in some SN and not others?

 

Jets are well-know features of accretion and mergers. If jets were formed in (some) SN progenitors, then the random direction of these jets on the sky would produce a velocity distribution of the ions they contain. As I start to appreciate that planetary nebula, nova and supernova lie on a continuum of binary interaction, it's interesting to see a pioneer in a paradigm shift in planetary nebulae, Noam Soker, investigate supernovae and jets.

[charles.tremblay.darveau]

Nice job Robin, I was just waiting for someone to post about this

[descott12]

Boy, this thing seemed way brighter when imaging as compared to capturing a spectrum. I thought all I had was noise but when I turned up my imaginoscope to high, I think I may have something. 

C8 + 178MM + SA-100. 1x17 seconds. All attempts to stack frames just caused more blur. But this single frame sort of looked like some real data once heavily smoothed. What do you think?  I think I might have the S2 "W absorption" and the 6150 valley.

 

Or is it all just garbage?

Attached Thumbnails

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[robin_astro]

Boy, this thing seemed way brighter when imaging as compared to capturing a spectrum.

Hi Dave,

 

A good first attempt

 

Yes spectroscopy needs a lot more exposure as you are spreading out the light thinly. (At least 6 magnitudes with the Star Analyser depending on the dispersion)

 

Supernovae don't need very high resolution spectra though so if you reduce your dispersion you will get a better result. Also 16 sec total is very short.(My SA100 example was 18x 20 seconds and about half the dispersion that you are using) Take 20 or 30 of your 16 sec exposures  and align and stack on the zero order. (Don't worry about the blur, the features are very broad and squeezing out more resolution adds very little detail)

 

Cheers

Robin

[robin_astro]

Here is your spectrum overlaid on a flux calibrated ALPY600 spectrum at R~500  (I took it a couple of days earlier on 20220426 so  there will have been some evolution)

 

 

You have captured the main features even in your single 16 sec exposure

 

One thing to watch for with faint objects is to chose the spectrum and sky background binning zones carefully. Here are the zones I used in ISIS with my Star Analyser spectrum 

 

 

(Note I used the optimised binning feature in ISIS here so the zone with the spectrum is deliberately wider than it need be, allowing ISIS to optimise the SNR by choosing the best rows within the spectrum. With conventional binning the zone should be narrower to just include the spectrum)

 

Cheers

Robin

Edited by robin_astro, 29 April 2022 - 08:43 AM.

[descott12]

Hey Robin,

Thanks for doing that! Not too bad at all! Yes, I forgot to experiment with the binning zone.  I have a little stacker program that I created and it stacks on a user selected area. I usually choose just the first-order signal and it usually works pretty well but for some reason, the spectra became very muddy and lost features. I will try it again and I think I will alter the dispersion as well. 

Thanks again for the overlay.

Cheers

Dave

[mwr]

This is how it looks with the Star Analyser tonight 

SA100 with the C11 and ATIK314 at 15 A/pixel  18x20sec

 

Cheers

Robin

 

SN2022hrs_SA100_20220424_annot_50pc.png

Yet another Star Analyser spectrum (SA-100) at low dispersion (11.9 A/pixel) recorded 05/01/2022 near maximum light at 12.4 mag with a DSLR (Canon 450 Da) and a VIXEN 5'' Newton. The typical SN Ia Si II absorption trough was well visible:

 

 

 

A comparison with a ProAm spectrum from the BAA database shows a good agreement:

 

 

In the NIR even the high velocity Calcium triplet was apparently detectable.  

 

The reference spectrum was recorded by Pro Am Jaroslaw Grzegorzek who has developed an impressive supernova search programme with remarkable success: http://spectroscopy.pl/index.html

Unfortunately, he abandoned his efforts recently: http://spectroscopy....asadnienie.html

I can understand his decision. Even the ancient Romans knew that the spirit of discovery is nourished by fame:

"Quippe gloria industria alitur; ubi eam dempseris ipsa per se virtus amara atque aspera est." (Sallust)

In fact, diligence is nourished by glory; when you take that away, virtue itself, on its own, is bitter and harsh.

[robin_astro]

 

Unfortunately, he abandoned his efforts recently: 

I too have suffered from this on occasion but my motto is "nil illegitimi carborundum" it irks me a bit but is not going to stop me keep doing what I enjoy

 

Cheers

Robin

Edited by robin_astro, 01 May 2022 - 01:52 PM.

[robin_astro]

Here are spectra (ALPY 600) of the core of the two galaxies which overlap in deep images so are both potential homes to this supernova,  together with a K3v star from Pickles as a reference

 

 

Note the redshifts

 

The two are quite different.

 

NGC4647 - a spiral galaxy with star forming regions and a supermassive black hole actively consuming material producing a strong H alpha emission

NGC4649 (M60) - an elliptical galaxy full of old stars, the light from the many millions of them captured in the slit resembling a K type star

 

(Type 1a supernova are produced by mature systems where at least one of the binary components has evolved to become a white dwarf)

 

Cheers

Robin

Edited by robin_astro, 01 May 2022 - 02:37 PM.

[mwr]

Here are spectra (ALPY 600) of the core of the two galaxies which overlap in deep images so are both potential homes to this supernova,  

I didn't realize that the home galaxy of this supernova has not yet been determined. Thanks for this hint! A paper suggests that we are currently witnessing the onset of the tidal interaction between NGC 4647 and M 60 (NGC 4649): https://www.aanda.or...7/aa5984-06.pdf

[robin_astro]

I didn't realize that the home galaxy of this supernova has not yet been determined. Thanks for this hint! A paper suggests that we are currently witnessing the onset of the tidal interaction between NGC 4647 and M 60 (NGC 4649): https://www.aanda.or...7/aa5984-06.pdf

I am not sure how you would determine which galaxy it is in. They have slightly (~300km/s) different systematic radial velocities but unlike type II where you have P Cygni Balmer lines with an unshifted emission component,  I am not sure if there are any features in the spectrum of a Ia which are unshifted by the explosion velocity making it difficult to pin down an exact value for the redshift. (Perhaps later in the nebular phase?). Given it is a Ia we should get a good  estimate of the distance but  the paper suggests we don't currently even know for certain which galaxy is in the foreground.  Maybe a study of the redshift of any interstellar absorption lines visible in the supernova spectrum from the galaxies  might hold a clue to which galaxy it is in and which is in the foreground?

 

Cheers

Robin

[mwr]

Given it is a Ia we should get a good  estimate of the distance but  the paper suggests we don't currently even know for certain which galaxy is in the foreground.  

Your post has prompted me to estimate the distance using the distance modulus and this SN Ia as a standard candle. Im my textbooks I couldn't find a value for the intergalactic extinction which should be substantial. However, a subsequent online literature search yielded a result that was completely unexpected and surprising to me as a hobbyist astronomer: The cosmic opacity is close to zero: κ = 0.0000 ± 0.0044 https://iopscience.i...357/ab1587/meta

In other words: There is no significant deviation from the transparency of the universe at the current observational data level. 

[mwr]

I am not sure how you would determine which galaxy it is in. 

May be the answer can be given by using the data in the following paper: https://adsabs.harva...ARA&A..30..359B

 

Supernovae Ia in spiral galaxies tend on the whole to be fainter and redder than their counterparts in elliptical galaxies, where the effect of extinction is expected to be smaller. The SNe Ia in Virgo cluster ellipticals are brighter by 0.35 mag (B mean 11.85 mag) than those in Virgo cluster spirals (B mean 12.2 mag), and there is a rather clear dependence between luminosity and color: the SNe Ia in spirals are on average 0.18 mag redder. Thanks to the AAVSO data the maximum B and V magnitudes of SN2022hrs can be determined and de de-reddened:

 

 

This gives a corrected value of B = 12.35 mag and (B-V)₀ = 0.22, which points to NGC 4647 (spiral) as home galaxy of SN2022hrs.

[robin_astro]

Except that it could be in  M60 with the additional extinction coming from NG4647  in the foreground?  (Note I am playing devil's advocate here)

 

That paper is pretty old in term of numbers of the limited supernovae available for study and knowledge about the variability in absolute magnitude and colour within Ia supernovae. (It even predates the recognition that the absolute magnitude depends on the shape of the light curve.)  A quick search pulled up this more recent paper which discusses how to disentangle inherent and extinction related variability in B-V

https://iopscience.i...538-4357/aa6038

 

 

Cheers

Robin

 

EDIT: the light curve shape dependence of absolute magnitude was known in 1992 but not the colour relationship

Edited by robin_astro, 07 May 2022 - 04:32 PM.