Starship Asterisk*

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

Ann wrote: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

Guest wrote:
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?

3.162277660168379 wrote:Absolutely wonderful and so educational.

Giza Guy wrote:

3.162277660168379 wrote:Absolutely wonderful and so educational.

sqrt 2 X sqrt 5 = 3.162277660168379

drollere wrote:
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

Ann wrote: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

Anthony Barreiro wrote:
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 wrote:Sounds good to me.

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

neufer wrote:

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

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

Ann wrote:

neufer wrote:

Ann wrote:
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.

http://astrobob.areavoices.com/2013/08/23/nova-in-delphinus-transforms-into-a-celestial-chameleon/ wrote:

[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.>>

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

geckzilla wrote:
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.

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

Surely you don't mean firing a flash.

neufer wrote:

geckzilla wrote:
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.