APOD: A Spectrum of Nova Delphini (2013 Aug 23)

[APOD Robot]

A Spectrum of Nova Delphini

Explanation: When a new star appeared in the constellation Delphinus late last week, astronomers found its spectrum hinted at the apparition's true nature. Now known as Nova Delphini, its visible light spectrum near maximum brightness is centered in this image of the nearby star field captured with prism and telescope on the night of August 16/17 at the Sternwarte Bülach, Switzerland. Strong absorption lines due to hydrogen atoms are seen as the darkest bands in the nova's spectrum, but the strong absorption lines are bordered along their redward edge by bright bands of emission. That pattern is the spectral signature of material blasted from a catalysmic binary system known as a classical nova. Other stars in field are fainter, identified by their Hipparcus catalog numbers, brightness in magnitudes, and spectral types. By chance, the faint emission line from planetary nebula NGC 6905 was also included, indicated at the lower right.

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[geckzilla]

It might be too much to ask but I am interested in a more detailed explanation for how this was made.

[Ann]

I love this picture, and I have already written a rather long comment on what can be learnt from these spectra. I'm going to paste my previous comment here:

The picture is indeed extremely informative! These are a few things we can learn from it:

1) We can see the relative position of Nova Delphini compared with other stars whose position we can find in the Hipparcos catalog. For example, we can see that Nova Delphini is located close to star HIP 100536.

2) We can compare the brightness of Nova Delphini with the brightness of other stars in the vicinity.

3) We can get an idea of the relative brightness of stars that are one, two or three magnitudes brighter or fainter than other stars. We can see, for example, that Nova Delphini is much brighter than eighth magnitude star HIP 100536 right next to it. We can see that the only star in the field whose brightness is in any way comparable to Nova Delphini is HIP 100754, whose V magnitude is 5.65. Clearly Nova Delphini is brighter than than HIP 100754, however.

4) We can get an idea of the colors of the stars. At upper right in the picture we can see two stars, blue HIP 100425 and red HIP 100346. These two stars are fairly similar in V (green) magnitude. We can clearly see, however, that the red part of the spectrum is brighter in red star HIP 100346 than in blue star HIP 100425. Still more remarkable is that we can see a lot of blue light from blue star HIP 100425, whereas the blue part of the spectrum is all but missing from red star HIP 100346.

5) We can check out the greenish color of OIII emission from planetary nebula NGC 6905.

6) We can see that all the colors of the spectrum are quite bright in Nova Delphini. Therefore its overall color should be fairly neutral. However, the blue part of the spectrum is so bright that Nova Delphini is certainly bluer than the Sun in this picture.

7) We can see a few obvious spectral lines in Nova Delphini, but not very many. Some of the lines appear to be hydrogen absorption lines from the Balmer series.

8) We can see that there appear to be bright emission lines right next to the dark absorption lines. Nova Delphini therefore appears to have a P Cygni spectrum, where dark absorption lines are bordered (on the red side) by bright emission lines. This feature means that we are looking at ejecta coming our way, or, in other words, we are looking at fragments from an explosion.

So the picture is indeed highly informative!

Ann

[Boomer12k]

Sort of Life Lines of a Star....."Let me read your future....oh, MY!!!!"...."I see you have an explosive temper..."

Very interesting comparisons.

:---[===] *

[Guest]

What a great APOD!

[3.162277660168379]

Absolutely wonderful and so educational. For me, this is probably the best APOD that gives me a better understanding of astronomy that I've ever seen!

[Guest]

I love this picture, and I have already written a rather long comment on what can be learnt from these spectra. I'm going to paste my previous comment here:

The picture is indeed extremely informative! These are a few things we can learn from it:

1) We can see the relative position of Nova Delphini compared with other stars whose position we can find in the Hipparcos catalog. For example, we can see that Nova Delphini is located close to star HIP 100536.

2) We can compare the brightness of Nova Delphini with the brightness of other stars in the vicinity.

3) We can get an idea of the relative brightness of stars that are one, two or three magnitudes brighter or fainter than other stars. We can see, for example, that Nova Delphini is much brighter than eighth magnitude star HIP 100536 right next to it. We can see that the only star in the field whose brightness is in any way comparable to Nova Delphini is HIP 100754, whose V magnitude is 5.65. Clearly Nova Delphini is brighter than than HIP 100754, however.

4) We can get an idea of the colors of the stars. At upper right in the picture we can see two stars, blue HIP 100425 and red HIP 100346. These two stars are fairly similar in V (green) magnitude. We can clearly see, however, that the red part of the spectrum is brighter in red star HIP 100346 than in blue star HIP 100425. Still more remarkable is that we can see a lot of blue light from blue star HIP 100425, whereas the blue part of the spectrum is all but missing from red star HIP 100346.

5) We can check out the greenish color of OIII emission from planetary nebula NGC 6905.

6) We can see that all the colors of the spectrum are quite bright in Nova Delphini. Therefore its overall color should be fairly neutral. However, the blue part of the spectrum is so bright that Nova Delphini is certainly bluer than the Sun in this picture.

7) We can see a few obvious spectral lines in Nova Delphini, but not very many. Some of the lines appear to be hydrogen absorption lines from the Balmer series.

8) We can see that there appear to be bright emission lines right next to the dark absorption lines. Nova Delphini therefore appears to have a P Cygni spectrum, where dark absorption lines are bordered (on the red side) by bright emission lines. This feature means that we are looking at ejecta coming our way, or, in other words, we are looking at fragments from an explosion.

So the picture is indeed highly informative!

Ann

Very cool. I am also curious as to how this image was constructed. What does the position on the horizontal and vertical axis represent? Is there spatial information here as well as spectral. Is this true color? Or, have the spectra been false colored to bring out featured in the UV?

[neufer]

[b][color=#0000FF]The visual appearance of diffraction grating spectra of a cluster of ordinary stars as seen through the telescope's eyepiece. [u][size=135]Without a cylindrical lens each spectra would appear as a streak instead[/size][/u].[/color][/b] http://laserstars.org/amateur/WolfRayet.htm

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Very cool. I am also curious as to how this image was constructed. What does the position on the horizontal and vertical axis represent? Is there spatial information here as well as spectral. Is this true color? Or, have the spectra been false colored to bring out featured in the UV?

1) A diffraction grating produces line spectral images on both sides
(i.e., right/left or top/bottom) of a focused 2D star field.

2) A cylindrical lens is then used to broaden each line spectra appropriately.

A 2D position thereby corresponds to a 2D position
but each star point source is transformed into a recognizable spectrum.

[Giza Guy]

Absolutely wonderful and so educational.

sqrt 2 X sqrt 5 = 3.162277660168379

[Joe Stieber]

Absolutely wonderful and so educational.

sqrt 2 X sqrt 5 = 3.162277660168379

Which, of course, equals the square root of 10 since: (sqrt 2) x (sqrt 5) = sqrt (2 x 5)

[drollere]

Hipparcos is the preferred spelling for the satellite and catalog.

[neufer]

Hipparcos is the preferred spelling for the satellite and catalog.

• And though thou hadst small Latine, and lesse Greeke,
  From thence to honour thee, I would not seeke

- From Ben Jonson's tribute to Shakespeare in the First Folio, 1623

[Anthony Barreiro]

I love this picture, and I have already written a rather long comment on what can be learnt from these spectra. I'm going to paste my previous comment here:

...

8) We can see that there appear to be bright emission lines right next to the dark absorption lines. Nova Delphini therefore appears to have a P Cygni spectrum, where dark absorption lines are bordered (on the red side) by bright emission lines. This feature means that we are looking at ejecta coming our way, or, in other words, we are looking at fragments from an explosion.

So the picture is indeed highly informative!

Ann

It is a beautiful and informative spectrum! You can really see the Hydrogen alpha, beta, and gamma absorption lines in Nova Delphini 2013's spectrum, and the emission lines at slightly longer wavelengths.

Why are the absorption lines blueshifted relative to the emission lines? I'm trying to picture the sequence of events, but my mental house of cards collapses before reaching a stable equilibrium. Hydrogen from a companion star falls onto a white dwarf, eventually triggering a thermonuclear explosion which we see as a nova. The explosion blows hydrogen out into space. The hydrogen in the cloud around the white dwarf is absorbing and emitting photons at the Balmer wavelengths, thus we see the Hydrogen alpha, etc. emission lines. The hydrogen in the gas that is directly between us and the still glowing nova absorbs photons at the Balmer wavelengths and re-emits them in random directions, causing the absorption lines. The gas that is directly between us and the white dwarf is traveling toward us faster than any of the other gas, so the absorption lines appear slightly blue-shifted.

After trying three or four times, I think I've figured it out. Is this right?

[neufer]

Why are the absorption lines blueshifted relative to the emission lines? I'm trying to picture the sequence of events, but my mental house of cards collapses before reaching a stable equilibrium. Hydrogen from a companion star falls onto a white dwarf, eventually triggering a thermonuclear explosion which we see as a nova. The explosion blows hydrogen out into space. The hydrogen in the cloud around the white dwarf is absorbing and emitting photons at the Balmer wavelengths, thus we see the Hydrogen alpha, etc. emission lines. The hydrogen in the gas that is directly between us and the still glowing nova absorbs photons at the Balmer wavelengths and re-emits them in random directions, causing the absorption lines. The gas that is directly between us and the white dwarf is traveling toward us faster than any of the other gas, so the absorption lines appear slightly blue-shifted.

After trying three or four times, I think I've figured it out. Is this right?

Sounds good to me.

[Anthony Barreiro]

Sounds good to me.

Thanks Art.

[Ann]

I can't help wondering why almost all the spectral lines of the nova seem to be from hydrogen. (There is a strong line deep into the blue-violet part of the spectrum that can't be a hydrogen line.)

Obviously the white dwarf is "sucking hydrogen" from its "partner's" outer atmosphere. The outer atmosphere of the poor cannibalized star should be strongly dominated by hydrogen. And when the nova has an outburst, it's blowing off the too-heavy snack of predominantly hydrogen that it has stolen from its binary companion. Even so, shouldn't we see a few obvious lines from other elements than hydrogen?

One possibility just might be that the temperature of whatever it is that produces most of the light here is perfect for creating hydrogen absorption lines. That temperature should be around 10,000 K, similar to the temperature and spectrum of an A-type star like Vega.

Is Nova Delphini a sort of explosive mega-Vega?

Ann

[neufer]

shouldn't we see a few obvious lines from other elements than hydrogen?

http://spaceweather.com/gallery/indiv_u ... d_id=85616

[Ann]

shouldn't we see a few obvious lines from other elements than hydrogen?

http://spaceweather.com/gallery/indiv_u ... d_id=85616

Thanks, Art, I appreciate your reply. However, I don't really understand it. The link you provided seems to say that we really only do see hydrogen lines in the spectrum of Nova Delphini. I was wondering about this very fact. Why aren't there other lines in the spectrum of Nova Delphini?

Ann

[neufer]

shouldn't we see a few obvious lines from other elements than hydrogen?

http://spaceweather.com/gallery/indiv_u ... d_id=85616

Thanks, Art, I appreciate your reply. However, I don't really understand it. The link you provided seems to say that we really only do see hydrogen lines in the spectrum of Nova Delphini. I was wondering about this very fact. Why aren't there other lines in the spectrum of Nova Delphini?

• The APOD clearly shows other lines which my link identifies as FeII lines.

[b][color=#FF0000]Nova Delphini 2013 on Aug. 21. Credit: John Chumack[/color][/b]

---

Nova in Delphinus transforms into a celestial chameleon
by Astrobob, Aug. 23, 2013

<<Through the telescope the nova has been a colorful sight. Early on it twinkled pale yellow but now has deepened in hue to yellow-orange. It’s still in the fireball phase with the white dwarf star hidden by fiery hydrogen gas and an expanding cloud of debris.

As novae evolve they’ll often turn from white or yellow to red. Emission of what’s called hydrogen alpha light gives novae their warm, red color. Hydrogen, the most common element in stars, gets excited through intense radiation or collisions with atoms (heat). Once energized, hydrogen’s electrons “move upstairs”, ie. jump from a lower energy level to a higher one. Just as quickly, they can drop back down “downstairs”. When they do, each releases a smidge of light in the deep red end of the rainbow spectrum called hydrogen alpha or H-alpha. Nova-red comes from electrons dropping from the “third floor” to the “second floor” inside the hydrogen atom.

Novae take on a pink or red color for several reasons according to Arne Henden, director of the American Association of Variable Star Observers (AAVSO). “Energy from the explosion gets absorbed by the surrounding material in a nova and re-emitted as H-alpha,” said Henden. Not only that but as the explosion expands over time, the same amount of energy is spread over a larger area. “The temperature drops,” said Henden, “causing the fireball to cool and turn redder on its own.” As the eruption expands and cools, materials blasted into the surrounding space condense into a shell of soot that absorbs that reddens the nova much the same way dusty air reddens the sun.

So why does it appear yellow-orange right now? “That’s the underlying continuum (bluish light from the explosion) mixing with the H-alpha from the expanding fireball. Red and blue together make orange.”

Finally, I’m often asked how far away the nova is. According to two studies based on the rate of decline in the nova’s brightness, the star is either 11,400 or 17,900 light years from Earth. Very far! That means it must be incredibly brilliant. A lot’s going on right now with Nova Delphini – an expanding fireball, formation of a debris cloud, cooling and reddening. And to think you can sample all this with little more than a pair of binoculars from your front yard. Amazing.>>

[TomRSpec]

It might be too much to ask but I am interested in a more detailed explanation for how this was made.

If you're an astro-imager, even with a small telescope and a video camera you can easily capture fascinating spectra like this for a wide range of stars, year 'round. The only new piece of hardware you need is a diffraction grating. One of the most popular is made by Paton Hawksley in the UK. For software, there is freeware or commercial products.

I started doing spectroscopy about four years ago and have found it to be absolutely fascinating.

For additional information, check out http://www.rspec-astro.com. Caveat: This is my commercial site, but there's plenty of free information, videos, and samples of what you can do.

Tom

[geckzilla]

Thanks, Tom. I found this image to be interesting:

Click to view full size image

What I've been wondering is whether it's a projection on to a black surface which one can then take a photo of or if the light goes straight into a camera something else. Sadly, I don't have a telescope so there are a few things that mystify me.

[neufer]

What I've been wondering is whether it's a projection on to a black surface which one can then take a photo of or if the light goes straight into a camera something else. Sadly, I don't have a telescope so there are a few things that mystify me.

Project on to a black surface and then take a flash photo of it.

[geckzilla]

What do you mean by flash photo? The "flash" part is confusing me. Surely you don't mean firing a flash.

[neufer]

What do you mean by flash photo? The "flash" part is confusing me.

Surely you don't mean firing a flash.

The "black surface" part is confusing me. (And don't call me Shirley.)

[alter-ego]

What I've been wondering is whether it's a projection on to a black surface which one can then take a photo of or if the light goes straight into a camera something else. Sadly, I don't have a telescope so there are a few things that mystify me.

Project on to a black surface and then take a flash photo of it.

My bet is the image was formed directly incident on a CCD. The detail clarity support a direct sensor illumination as opposed to an image capture from a scattering surface. Also the use of a weak cylindrical lens (as Art posted) is the probable setup. The simplest method I'd use to recreate this image is to properly orient a grating or prism in from of my telescope (aperture down so that the prism operates on all the collected light). The APOD dispersion axis is oriented north/south so it is possible to generate the picture without a cylindrical lens by letting the stars drift in the field (earth rotation/differential drive). This would be my poor-man's approach, and likely not as good a quality. Alternatively, I'd use a weak cylindrical lens in place of a Barlow lens to broaden the image in the non-dispersive direction, and accurately track the stars.

Note, to generate the observed visible dispersion of about 1 degree means the telescope is needs to be pointed about 10 degrees due north or south of the target star (assuming a glass prism is used).