If you’ve missed the astronomical news in the last few days, a new star is now decorating (temporarily) the northern edge of Delphinus. In fact, it’s so close to the edge it almost landed in both Vulpecula and Sagitta. Currently it’s shining at a magnitude of somewhere between 4.5 and 5.0, depending on what source you happen to read. The latest AAVSO light curve shows readings in that range as well, with an average magnitude of about 4.7 to 4.8. Until it erupted this past Wednesday (August 14th), it was an obscure 17th magnitude star that escaped notice. That change in magnitude means this star is now 62,000 time brighter (2.5112) than it was a week ago.
How does a nova end up on a blog about double stars, you ask? It’s here because its new found brilliance is caused precisely by the fact that it is a double star. Novas – not to be confused with supernovas, which are mammoth explosions that leave only a remnant behind – are caused by the transfer of material from a parent star to an orbiting white dwarf. When that material accumulates to the point that it causes the white dwarf to become thermally unstable, a sudden release (aka explosion) occurs. And that’s what we’re seeing now.
So where is it and how can you find it? If you’re not familiar with this area of the sky, take your time because this is a densely populated area of stars thanks to their Milky Way location. Binoculars are the best way to find the nova – once you’re confident of its location, you’ll have less trouble finding it in a telescope.
I started from Sagitta, which is probably the easiest way to get there (click here to open the chart above in a second window). If you’re familiar with the area, the nova is located almost exactly halfway between 5.05 magnitude Eta (η) Sagittae and 4.80 magnitude 29 Vulpeculae. Otherwise, you can star hop to it by first locating the arrow that forms the small constellation of Sagitta (Sge). Once you’ve done that, center you binoculars or finder scope on Gamma (γ) and Eta (η) Sagittae at the east end of the arrow. From there, hop one and half degrees to 6.50 magnitude Theta (θ) Sge and 6.20 magnitude HIP 99445, which form a distinctive pair. Then proceed northeast almost two degrees to 18 Sge (magnitude 6.10), and then hop east two more degrees to HIP 100754 (magnitude 5.65). You should see the nova sitting slightly less than two degrees to the southwest, parked next to 8.07 magnitude HIP 100536 .
Or, if you’re using a GOTO mount, the coordinates are 20h 23.3m, +20° 46’.
It took a couple of nights before the weather became cooperative, but I had my first look at Nova Delphini shortly after midnight on the morning of August 18th;
Most people initially reported the nova as having a distinct blue-white color, but by the time I got to it, it had begun to transition to pure white, although I did see a hint of yellow in it when I looked carefully. If it behaves normally, the yellow should become more pronounced in the next few days. I also noticed a strange quality to the light which is hard to describe, as if it was very intense and more energetic than any of the stars around it similar in brightness. When I compared it to 29 Vulpeculae (magnitude 4.80) and Eta (η) Sagittae (magnitude 5.05), it seemed to me to be just a slight bit brighter, perhaps about magnitude 4.60 or so.
It now appears as though the nova peaked at a magnitude of about 4.4 a few days ago and has begun to decrease slightly in brightness and may be leveling off. How long it will remain at the current magnitude, or what it will do next, is anyone’s guess. I’ve tracked down a lot of faint novas in distant galaxies, but this is the first one I’ve had an opportunity to look at that is bright enough to be seen with the naked eye. Novas this bright are rare, so if you have a chance to look, don’t miss it.
Update 8/19: Had another look last night (24 hours after the observation above) and was surprised to see the nova appeared distinctly yellow in my 10×30 Canon IS binoculars — the prior night it was distinctly white with a tinge of blue. It also has dimmed slightly, settling about halfway between 4.80 magnitude 29 Vul and 5.05 magnitude Eta (η) Sge — I’ll call it 4.95.
Here’s a second sketch made at 0100 UT on 8/19 showing a wider view of the surrounding star field, along with the identification of three stars that form a triangle, with the nova near the center. HD 351956 is a 9.0 magnitude star, HD 352087 is at 9.8 magnitude, and the magnitude of HIP 100536 is supposed to be 8.07, although it didn’t appear to me to be the the brightest of the three:
You can see the yellow is more pronounced in this sketch in comparison to the first one above. Part of that difference is due to the fact that colors have a warmer tone in an achromatic refractor in comparison to the mirror based SCT used for the other sketch, but even at that, the color in the refractor was very similar to what I saw in the binoculars.
Update 8/20: Studied the nova at 2300 (0600 UT 8-21) with 10×30 binoculars for about twenty minutes, comparing the nova’s brightness with 29 Vul (4.80) and Eta (η) Sagittae (5.05). It struck me as almost being equal to Eta Sge, so I’ll call it 5.0 for the night. The yellow color may have increased slightly, but with the moon being almost full and illuminating some moisture in the air, it was really hard to be sure.
As to where it will go from here, see these interesting AAVSO comments: What’s in store for Nova Del 2013?
Update 8/21: Took a look again at about midnight (0700 UT 8/21) with both the 10×30 binoculars and a 90mm refractor. The yellow color may have increased slightly — again, the moon makes it hard to be sure — but the nova has definitely continued its decline in magnitude. It’s now very definitely fainter than 5.05 magnitude Eta (η) Sge — my estimate is about 5.2. The latest AAVSO light curve confirms the decline. Here’s a comparison chart (scroll down to the bottom of the page) of some other nearby stars that can be used to estimate magnitude. The stars identified to the left (east) of the nova form a very distinctive pattern in an 8×50 finder (with the nova still in the field of view) — you can’t miss them!
Update 8/22: It looks like Nova Delphini 2013 is declining in magnitude fairly quickly. At 2200 (0500 8/22 UT), it seemed to be just slightly brighter than 5.65 magnitude HIP 100754, which is located about a degree to the northeast (click here to open the chart above in a second window). I was interrupted by clouds for a couple of hours, but when they cleared, I cornered the nova in a four inch f/13 refratcor. HIP 100754 was just out of view at the northeast edge of the field, so I was able to pan the scope up and down to compare the two stars. In the telescope, I could see the nova was clearly fainter by two- to three-tenths of a magnitude. So as of 0700 UT 8/22, I estimated its magnitude at 5.9, which is a significant drop from the estimated 5.2 of the previous evening.
The forecast is for clouds for the next several days, so that will probably be it for visual updates for a while. In the meantime, if you’re interested in some basic information about the spectroscopy of the nova, here’s a good explanation I just came across.
Update 8/25: Surprise clear night on evening of 8/24, so I checked the nova to see how much it had faded. In binoculars at 2200 8/24 (0500 8/25 UT), it was noticeably fainter, and darker in color. It actually has a pronounced orange tint, but in 8×30 binoculars, even against a dark sky, that orange is very hard to detect. I compared the nova with 6.45 magnitude HIP 100779, which is about a degree to the southeast (here’s the chart again), and found them almost identical in brightness. HIP 100779 has a spectral classification of K0, so color-wise they make a good match for magnitude comparison. I turned my six inch f/10 in that direction and found the orange color much easier to see (18mm Radian, 84x), but even then, due to the faintness, it was a subtle thing. Still an impressive sight, though, when you think carefully about what you’re looking at.
Update 8/31: I finally had another look at the fading nova at midnight (0700 8/31 UT), with both binoculars and a 9.25 inch SCT. In binoculars, you have to know exactly where to look now in order to see it since it’s basically faded to the point where it no longer stands out from the background stars. I compared it with the star used above, 6.45 magnitude HIP 100779, and another star a degree to its west, 7.13 magnitude HIP 100500 (now shown on the chart above, or click here). That one is a class G5 star, so it’s a pretty good match color-wise for a comparison star. The nova struck me as being closer in magnitude to the dimmer of the two comparison stars, so I’ll call it 6.8, which puts it in the bottom range of the current AAVSO light curve. That curve, by the way, shows a continuing decline in magnitude, although it does seem to be leveling off very slightly.
In the 9.25 inch SCT (an Edge version), the best description I can think of for color is a luscious deep gold leaning in the direction of orange. A refractor would probably enhance the orange over the gold, but either way, it’s a beautiful sight against a background of deep black sky. Better look soon if you haven’t — the nova is fading in magnitude to the point that color will soon be hard to detect.
Unless of course it suddenly brightens up again. You never know for sure with these things.
I’ll leave this story here for the time being unless there’s a significant change in magnitude or some other unexpected event.