Archive for August, 2013

Nova Del 2013 continues to decline

August 31, 2013

I just came inside from making my first visual estimate of Nova Del 2013 in a few days and my 8th in total: magnitude 6.8.

Here’s the latest light curve (with my observation at right; purple and in the cross-hairs).

NovaDel2013Aug31

It’s faded more than 2 magnitudes since peaking mid-August. If this keeps up, it won’t be too many more days before I need to think about breaking out my 8″ SCT to estimate the nova’s magnitude from my suburban location.

Latest Nova Del 2013 observation

August 21, 2013

There are currently almost 24 million variable star observations in the AAVSO International Database, as per http://www.aavso.org:

MyAug21NovaDel2013Ob

The 23,935,137th observation was of Nova Del 2013, my 111th variable star observation. All 111 have been visual estimates; a modest number.

Here’s the light curve now:

NovaDel2013Aug21

Adding a binned means series (0.25 days per bin) and a polynomial fit (both against the Visual series) gives an impression of the overall changes since the initial outburst.

From looking at this, the nova seems to be on a gradual decline, but in fact it could still rise in magnitude again as Mike Simonsen points out in this AAVSO post with reference to another nova in Delphinus in the 1960s.

So, keep observing!

Finding Nova Delphini 2013

August 20, 2013

I’ve talked about Nova Delphini 2013 and shown light curves but if you want to observe the nova, how do you find it?

The first thing to say is that now is a good time to look. As I write this, it’s still bright (magnitude 5.2 but starting a decline).

NovaDel2013Aug20

No-one knows  exactly what it will do next.

Start by finding the distinctive (it looks like  tadpole to me) constellation of Delphinus, near Aquila. The following Stellarium screenshot may help. The ringed cross hairs show the approximate location of the nova. Tonight the moon (not shown) is off to the right of bright Altair, a useful reference point.

NovaDel2013

Go to AAVSO’s variable star plotter and enter Nova Del 2013 and 12531AWO into the text boxes shown below. Select the “Printable” option further down on the form and click “Plot Chart”.

Creating 12531AWO

This will give you a finder chart that looks like this (click on it to enlarge):

southern_finder

The nova is marked with cross hairs. The numbers are the magnitude of known comparison stars (without full-stops, so 47 = 4.7). The task is to determine which comparison star is closest to the nova’s magnitude or more likely, which pair of comparison stars the nova falls between in brightness.

This finder chart is rich in comparison stars, and the main asterism of the “head” of Delphinus is quite distinct. I use 7×50 binoculars to observe the nova and comparison stars from my suburban backyard.

So, weather permitting, go out and have a look while the nova is still bright enough to be fairly easy to spot. Take your time and enjoy lingering over a patch of sky you may not normally and if you spot the nova, think about that shell of material that’s expanding at around 1000 km/sec from an explosion of about 30 earth masses of matter accumulated onto a white dwarf from its companion with a luminosity increase of 100,000 suns.

Potentially perspective-changing stuff…

Nova Delphini 2013 at “standstill”

August 19, 2013

We’re three days further along and Nova Delphini 2013, having so far peaked at magnitude 4.3, has been more or less at standstill within a range of half a magnitude since about August 17. The visual and Johnson V light curve is shown below.

NovaDel2013Aug19a

My observations are shown in purple (5.6, 4.7, 4.9), the first under the cross hairs. Click the image to enlarge it. The last two were more difficult to make than the first because of intermittent, fast moving cloud, an almost full moon, and in the case of the third observation (at right) low elevation (soon after rising).

There certainly seems to be some discrepant observations. The nova is being observed in many more bands than are shown here, e.g. infrared. Here’s a multi-band (12) light curve for the same time period.

NovaDel2013Aug19b

Note that different bands have different magnitude ranges.

What will Nova Del  2013 do next? Decline or brighten?

Nova Delphini 2013

August 16, 2013

A day later and PNV J20233073+2046041 has lost the “possible” in “possible nova” and is now designated Nova Delphinus 2013.

Since I observed it last night (see cross-hair below), Nova Del 2013 has brightened more than another magnitude from around 5.5 to 4.5 as can be seen from the following AAVSO visual and Johnson V light curve.

NovaDel2013Aug16

The following shows a pre-brightening observation (shown in red at bottom left) that was added to the AAVSO International Database since last night.

NovaDel2013Aug16PlusPrediscoveryFT

Now, that’s a so-called “fainter than” observation which means that it was recorded as being fainter than magnitude 9.8.

The Variable Star Index entry suggests that it was substantially dimmer than this before the outburst.

It’s cloudy here in Adelaide tonight and the next few days don’t look promising so I’m really glad I had the chance to see this last night. I’m itching to be able to see it again though!

Addition: I just came back inside after being out in the backyard for an hour. It looked as thought it might clear long enough to make an estimate, but sadly not.

Possible nova in Delphinus

August 15, 2013

I’ve just been out in my back yard observing a possible nova in Delphinus discovered within the last day, currently designated PNV J20233073+2046041. This is a bright object. I made a visual estimate via 7×50 binoculars just now of 5.6.

I was alerted to the nova through a Variable Stars South mailing list and obtained further details (e.g. finder chart) on the AAVSO nova forum.

Here’s an excerpt from the CBAT Transient Objects site:

2013 08 14.584

Discovered by Koichi Itagaki, Yamagata, Japan, using 0.18-m reflector + unfiltered CCD. This Nova was confirmed on the frames taken on August 14.750 UT using 0.60-m f/5.7 reflector + unfiltered CCD after discovery. Then CCD magnitude is 6.3. Also nothing is visible at this location on his past frames (limiting mag.= 13.0) taken on 2013 August 13.565 UT.

The latest AAVSO light curve for the nova is shown below, with my observation under the cross-hairs.

PNV J20233073+2046041

While I was composing this post, another visual estimate was added to the AAVSO International Database. Visual estimates have an accuracy of about a tenth of a magnitude, so the fact that recent observations (5.5 and 5.6) differ by 0.1 of a magnitude is not too surprising.

It will be interesting to see how this object evolves in the near future. I wouldn’t be surprised to see amateur spectroscopy in the next few days.

Mike Simonsen points to a nice colour image of the nova.