* Astronomy

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 an "extra star" in an otherwise rather starless portion of the constellation of Pyxis.
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.
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Credit: ESO/M. Kornmesser

The recurrent nova T Pyxidis is having an outburst after nearly 45 years. It has been steady at magnitude 15.5 or so until it was discovered on the rise by the noted Hawaiian variable star and meteor observer Mike Linnolt on April 14th.  As of April 18th it was up to around 7.7 magnitude, If it behaves as it did during the last outburst in December 1966 it will reach 6.5 magnitude by mid-May. I have yet to see it because of poor weather, but hope to try to see it soon. Previous outbursts occurred in 1890, 1902, 1920, and 1944. There are only ten known galactic recurrent novae.
The star T Pyxidis is also one of only two known white dwarf binary star systems whose mass is close to the Chandraseker limit (1.4 Solar Masses), making it a type-Ia supernova candidate. The other one is U Scorpii, which may also blow soon. At a distance of about 3,000 light years, if T Pyxidis should go supernova it will become -9 magnitude and be visible in the daytime! Don't worry about ill effects though if it does, as it is too far to cause any trouble. Also, the chance of this happening in our lifetime is very low.

Source 

The recurrent nova T Pyxidis has been discovered in outburst. It was detected by M. Linnolt (Hawaii, United States) at a visual magnitude of 13.0 on 2011 April 14.2931 (JD 2455665.7931), and confirmed by A. Plummer (m(vis)=12.2, JD 2455665.8847) and S. Kerr (m(vis)=11.3, JD 2455665.9410). This is the first outburst of T Pyx since December 7, 1966, nearly 45 years. Observations of this rare outburster are urgently requested, beginning immediately.
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Title: The orbital period and system parameters of the recurrent nova T Pyx
Authors: Helena Uthas, Christian Knigge, Danny Steeghs

T Pyx is a luminous recurrent nova that accretes at a much higher rate than is expected for its photometrically determined orbital period of about 1.8 hours. We here provide the first spectroscopic confirmation of the orbital period, P =1.829 hours (f=13.118368(11) c/d), based on time-resolved optical spectroscopy obtained at the VLT and the Magellan telescopes. We also derive an upper limit of the velocity semi-amplitude of the white dwarf, K1 = 17.9 ±1.6 km/s, and estimate a mass ratio of q = 0.20 ±0.03. If the mass of the donor star is estimated using the period-density relation and theoretical main-sequence mass-radius relation for a slightly inflated donor star, we find M2 = 0.14 ±0.03 Msun. This implies a mass of the primary white dwarf M1 = 0.7 ±0.2 Msun. If the white-dwarf mass is > 1 Msun, as classical nova models imply, the donor mass must be even higher. We therefore rule out the possibility that T Pyx has evolved beyond the period minimum for cataclysmic variables. We find that the system inclination is constrained to be approximately 10 degrees, confirming the expectation that T Pyx is a low-inclination system. We also discuss some of the evolutionary implications of the emerging physical picture of T Pyx. In particular, we show that epochs of enhanced mass transfer (like the present) may accelerate or even dominate the overall evolution of the system, even if they are relatively short-lived. We also point out that such phases may be relevant to the evolution of cataclysmic variables more generally.

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