Near-Infrared Observations of Recurrent Nova T Pyx In Outburst

ATel #3297; D. P.K. Banerjee and N. M. Ashok (Physical Research Laboratory, Ahmedabad, India)
on 20 Apr 2011; 11:58 UT
Credential Certification: Sachindra Naik (snaik@prl.res.in)

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We report photometric and spectroscopic near-IR observations (1.08 to 2.3 micron) of the recent 2011 outburst of the recurrent nova T Pyx using the 1.2m Mount Abu telescope and the NICMOS3 imager-cum-spectrograph. Photometric observations were centered around mean times of 2011 April 14.6, 15.6 and 16.6 UT respectively and followed immediately by spectroscopy. In its present avatar, T Pyx quickly brightened from J, H, K magnitudes of (9.88, 9.70, 9.70) on 2011 April 14.6 UT to (7.45, 7.30, 6.94) and (6.81, 6.70, 6.37) on the subsequent two nights (typical error 0.03 mag., note: sky not photometric on 2011 April 14 UT ). Though it was attempted, the faintness of the nova did not permit recording a useful spectra on 2011 April 14.6 UT . On 2011 April 15.6 and 16.6 UT the spectra are fairly similar and prominently display Paschen and Brackett lines of Hydrogen. HeI lines are strong, right from the start of the outburst, as similarly seen in the latest outbursts of recurrent novae RS Oph ( 2006, ApJ, 653, L141) and U Sco (2010, MNRAS, 408, L71) covered from Mt Abu . Apart from the HeI 1.0830 micron and 2.0585 micron features, which are transitionally expected to be strong, other HeI lines like 1.7002, 2.1120 and 2.1132 micron are also clearly detected at significant strength. In comparison to the optical region (ref: the SALT spectrum in A Tel 3289), few strong NI lines are expected in the JHK bands, but the NI blend due to the lines at 1.2461 and 1.2469 microns is clearly detected. The OI 1.1287 and 1.3164 micron lines are seen, but there is a possibility that the ratio of OI 1.1287 to 1.3164 micron line is much lower than that generally seen early in nova outbursts, possibly indicating that continuum fluorescence, in addition to Lyman Beta fluorescence, is playing a significant part in the excitation. However, we caution that this aspect needs to be established more robustly given the caveat that OI 1.1287 micron line lies in a region of difficult atmospheric transmission hindering accurate determination of its strength. The strengths of available counterparts of OI lines in the optical, both continuum and Lyman Beta fluoresced, should help in resolving the issue. Prominent P-Cygni profiles are seen in the Br Gamma, Paschen Beta and HeI 2.0585 micron lines on both nights.