The 2011 outburst of the recurrent novaT Pyx. Evidence for a face-on bipolar ejection

Source: arXiv


We report on near-IR interferometric observations of the outburst of the
recurrent nova T Pyx. We obtained near-IR observations of T Pyx at dates
ranging from t=2.37d to t=48.2d after the outburst, with the CLASSIC
recombiner, located at the CHARA array, and with the PIONIER and AMBER
recombiners, located at the VLTI array. These data are supplemented with
near-IR photometry and spectra obtained at Mount Abu, India. Slow expansion
velocities were measured (<300km/s) before t=20d (assuming D=3.5kpc). From
t=28d on, the AMBER and PIONIER continuum visibilities (K and H band,
respectively) are best simulated with a two component model consisting of an
unresolved source plus an extended source whose expansion velocity onto the sky
plane is lower than 700km/s. The expansion of the Brgamma line forming region,
as inferred at t=28d and t=35d is slightly larger, implying velocities in the
range 500-800km/s, still strikingly lower than the velocities of 1300-1600km/s
inferred from the Doppler width of the line. Moreover, a remarkable pattern was
observed in the Brgamma differential phases. A semi-quantitative model using a
bipolar flow with a contrast of 2 between the pole and equator velocities, an
inclination of i=15^{\circ} and a position angle P.A.=110^{\circ} provides a
good match to the AMBER observables (spectra, differential visibilities and
phases). At t=48d, a PIONIER dataset confirms the two component nature of the H
band emission, consisting of an unresolved stellar source and an extended
region whose appearance is circular and symmetric within error bars.These
observations are most simply interpreted within the frame of a bipolar model,
oriented nearly face-on. This finding has profound implications for the
interpretation of past, current and future observations of the expanding

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