Weekend Observing Project: T Pyxidis

by Tammy Plotner on April 30, 2011

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Are you ready to observe a nova event which can be caught in simple binoculars? Then open your eyes wide and locate T Pyxidis! Right now it’s showing up as just slightly fainter than magnitude 7, which means it is going to appear as an “extra star” in an otherwise rather starless portion of the constellation of Pyxis. Are you ready? Then let’s dance…

T Pyxidis is actually a binary star – one much like our own Sun with a white dwarf companion. Thanks to its diminuative, heavy-weight companion, matter from the primary star is always being drawn toward the secondary causing periodic thermonuclear explosions. Since there hasn’t been any real activity in about 45 years, astronomers believed T Pyx could possibly have began evolving into an entirely new system and activity wouldn’t occur perhaps for centuries. But they were wrong…

With a normal magnitude of 15.5, T Pyxidis would only be visible to some of the largest of amateur telescopes, but right now it can easily be spotted with average binoculars. The first finder chart seen on this page will get you in the right area and the one below will get you spot on (RA 09h 04m 41.50s Dec -32° 22′ 47.5″).

The fun part about observing T Pxidis is that it’s an object well suited for both hemispheres – one where the south is a bit more favored than the north – and all the “buzz” that goes with it. According to many sources, the white dwarf may be nearing its Chandrasekhar limit and become a Type 1a supernova when it collapses under its own weight. Says Edward Sion (et al); “The recurrent nova T Pyxidis has had 5 recorded thermonuclear explosions, more than any other recurrent nova, with an average time between nova outbursts of 19 years. However, it has been 44 years since its last nova outburst in 1966, making it long overdue for the next nova (supernova?). ”

However, don’t worry about this 3,300 light year distant stellar explosion happening any time soon. It’s estimated that kind of action may take as long as another couple of million years. “A key fact about T Pyx is that its accretion rate has been secularly declining since before the 1890 eruption, with the current rate being only 3% of its earlier rate. The decline in the observed accretion rate shows that the supersoft source is not self-sustaining, and we calculate that the accretion in T Pyx will effectively stop in upcoming decades.” say Bradley E. Schaefer (et al). “With this, T Pyx will enter a state of hibernation, lasting for an estimated 2,600,000 years, before gravitational radiation brings the system into contact again. Thus, T Pyx has an evolutionary cycle going from an ordinary CV state, to its current RN state, to a future hibernation state, and then repeating this cycle.”

But don’t you wait that long to observe it. For the next week or so, the Moon won’t interfere with your early evening chance to see this very cool cosmic customer!

About 

Tammy is a professional astronomy author, President Emeritus of Warren Rupp Observatory and retired Astronomical League Executive Secretary. She’s received a vast number of astronomy achievement and observing awards, including the Great Lakes Astronomy Achievement Award, RG Wright Service Award and the first woman astronomer to achieve Comet Hunter's Gold Status.

Question April 30, 2011 at 5:32 AM

cloudy!

GBendt April 30, 2011 at 8:15 AM

Currently, T Pyxidis is too close to the horizon for observers at higher northern latitudes. Even Miami is too much to the north now to allow seeing constellation Pyxis on a dark sky.
In April and Mai, the southern hemisphere is much better for observing T Pyxidis.

Andrew James April 30, 2011 at 12:10 PM

Good to see you use Megastar. There are few of us left these days.
When will they bring out Megastar 6?

T Pyx was 7.1 magnitude about a day or two ago. Maximum will be about 6.6 or 6.7 in about two or three weeks time.
Looks like it has gone into the past small spike, before the final plunge in brightness. Perhaps the expelled shell is on the edge of going from opaque to a translucent phase, and only after seventeen days. Based on past experience, the mean expansion of 450km.sec^-1 ; all expanding within just a billion kilometres or so since the ejection. (The outer shell moves about three times faster, around 1600 km.sec^-1, if previous outbursts are anything to go by.)
We can probably already assume the mass transfer from the star to the white dwarf has already just beginning again, for the next burp in the next five or six decades. (The progression is the outburst years of 1890, 1902, 1921, 1944. 1966 and now 2011; with the differences being 12, 19, 24, 22 then 41 years.
The “decline in the observed accretion rate” is obvious, but the geometric progression means the next will be 45 or 46 years (c,2056 or 2057 AD) Saying ” the accretion in T Pyx will effectively stop in upcoming decades.” say Bradley E. Schaefer et. al.)” doesn’t hold much water. (As the maxima magnitude is also slightly increasing after each burp by about 0.2 or 0.3 just mean the rate of transfer is slightly slower, but it is adding slightly more mass after detonated.
For me, there is no or little evidence when this process will stop, but the longer duration between detonations mean you will only probably see an event twice in a lifetime.
Just 100 days from now it will be below 11th magnitude when it goes back to sleeping mode. Interesting future will dog this object for the next century or so, but for now, just observe it while you can!

Aero-D May 1, 2011 at 1:12 AM

OK, I can find PYXIS on my star finder, what would be handy would be how far above the horizon to look. RA’s and DA’s don’t help us amateur binocular types.

I’ll go give it a try!
Thanks Universetoday.com, love this site!

Tammy Plotner May 2, 2011 at 1:07 AM

hey, aero-d…

i live in mid-northern ohio – approximately 42N. for me, alpha (a) pyxis is low, roughly around 20 degrees (or a handspan at arm’s length) above the south/southwest horizon when it’s good and dark. how low you can see along the horizon has a great deal to do with how much atmosphere and light pollution you have in your area – including happy things like trees and buildings – but using binoculars and hopping from one familiar star pattern to the next will definately help! if all else fails, roughly judge the distance between procyon and regulus – then drop due south from that mid-point about 1.5 times the distance again.

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