Nova In Delphinus Transforms Into A Celestial Chameleon

I plotted my observations of Nova Delphini 2013 through Aug. 22 on a simple graph to create a curve showing how the nova’s brightness has changed with time. The bottom axis shows the date; the vertical axis the nova’s magnitude. After a leap from 17th magnitude (far left) to around 4 1/2, the star has been slowly fading.

Time to check in on this month’s bright nova in Delphinus. After plateauing at magnitude 5.0 last weekend, Nova Del 2013 has been slowly fading ever since. By last night it had slid to 5.8 or just a tad brighter than the naked eye limit. The simple plot or light curve I compiled using my own binocular observations clearly shows its steady decline. Whether the star will continue to fade or bounce back is anyone’s guess. Novae can surprise just like comets do. They can also change color as we’ll see in a moment.

Chart to help you find the nova and estimate its brightness down to around magnitude 7.1. Click for larger version.

Now that the moon is rising later, skywatchers with dark, rural skies should be able to spot the nova with the naked eye again very soon. If you’ve been keeping a log of its brightness, click HERE for instructions on how to build your own light curve. I’ve included an updated chart for you to use to estimate the star’s brightness in the coming nights.

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.

Closeup of prominences along the limb of the sun seen during a 1999 total solar eclipse. The flames glow in red H-alpha light. Nebulas also give off the familiar red of H-alpha as stars buried within them excite hydrogen gas to glow. Credit: Luc Viatour

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).

Nova Delphini 2013 on Aug. 21. Credit: John Chumack

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).

Nova illustration with an expanding cloud of debris surrounding central fireball emitting red hydrogen-alpha light.

“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 the most recent study (reported 8/23), based on the rate of decline of the nova’s brightness, the star is some 13,000 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.

8 Responses

  1. Gavin

    Hi Bob, I always enjoy reading your articles! Regarding the distance, it seems from the following that it has been estimated at between 3.5 to 5.5 kpc:
    (see around two-thirds down the article).
    I’m not sure how they derived that distance estimate or whether it’s accurate. If correct, the nova must be intrinsically very bright compared to our Sun!

    1. astrobob

      Thanks Gavin. I went halfway between two other estimates including a “ballpark” one by Henden. Thanks for the Atel number.

  2. Thanks for the H-alpha explanation, Bob. I’ve been looking for some information to quench my curiosity about the spectroscopy of the nova. Since its brightness has been decreasing during the last few days while the H-alpha and -beta emissions have increased, I thought maybe there was in inverse relationship there. If I understand your explanation correctly, there wouldn’t necessarily be any relation at all between those events.

    Good info — I’ll add a link to this piece on my blog!


    1. astrobob

      Thanks John. I had bits and pieces of an explanation but talking with Arne helped clarify. Nice blog by the way! I’m a double star fan, too.

  3. Sean

    Hey Bob. Thanks to ur great maps here and on universe today i’m pretty sure i found the nova in binoculars 2nite, first night i’ve attempted to find it. First tried to find it from a nearby park without bringing any maps and without having memorized them in detail, and i was pretty sure i had found 29 vulpeculae but the jumble of stars nearby from there with many of similar brightness had me confused. went back home and from my 3rd floor apartment went out onto the fire escape a couple of times, going back and forth from my computer to look at the maps and i think i have it, to me it appears very similar in brightness to the 5.7 star but i am no expert at magnitude estimates, and i thought it also looked similar to some of the brighter stars in the “X” pattern which lies i guess SE of the nova. (the X could b considered an H as well, since there are 2 stars in the central portion which u could interpret as the central bar.) There isn’t any other star of similar magnitude right there, which i am mistaking it for, correct? the closest ones of similar magnitude, like i said, seem to be the 5.7 one and some of the brighter ones within the letter pattern. i also tried to view Neptune and Iris 2nite, but man, they are a real stretch 4 me with my 10×50’s. i’m in a moderately light-polluted somewhat urban area so perhaps this is a factor? the moon wasn’t very high so this might have had a slight effect as well. my contacts might b slightly less than perfectly clean which won’t help either. i think there are 2 very dim stars “near” Iris which would make kind of a tight triangle when seen with it tonight, and i could definitely make them out using averted vision but not sure i could see anything where Iris should have been. similar experience with Neptune, tho i think i saw something BARELY using averted vision where it should have been, unless there’s another dim star right nearby there. i was going from sigma aquarii. there is another star right “below” it as seen around 10PM, and 2 much dimmer ones that are perpendicular in position from sigma compared to the one “below”, left and right, the left one a little brighter and farther than the one at right which is very dim indeed. so Neptune should be “above” and to the right of this dim one, by a little bit, and i MIGHT have seen something there avertedly. sorry, i find it annoying to constantly use cardinal directions. i am also trying to narrow down which stars surround the N american nebula, as i am not sure i can really see it. anyhow, definitely saw a nice Kappa cygnid tonight as well. wishing u clear skies!

    1. astrobob

      Glad to hear you found the nova. I’ve been keeping close track of it and after a steady decline to 6.0 mag. last night, it’s still at 6.0 tonight. It does look very similar to the 5.7 star but is definitely a little fainter. Defocus your binoculars some to turn the stars into disks and you’ll find it easier to see small magnitude differences. Neptune from an urban area would be tough, but it’s easy from the outer suburbs and countryside with 10x50s.

      1. Richard Keen

        Bob, I also got 6.0 a couple of nights ago, aroung 10 pm Duluth Time on the 23rd.
        Tonight’s the 25th, the 38th anniversary of the outburst of Nova Cygni – the brightest Nova in the past 71 years. We’re about due for a brighter one, and a supernova, too.

        1. astrobob

          Thanks for your estimate. Last night the 24th – interestingly – the nova held on at 6.0 after a steady decline the previous nights.

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