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The outburst light curve of Nova KT Eridani from Solar Mass Ejection Imager (SMEI) observations

ATel #2558; R. Hounsell (Liverpool JMU), M. F. Bode (Liverpool JMU), P. Hick (UCSD/CASS), A. Buffington (UCSD/CASS), B. Jackson (UCSD/CASS), J. Clover (UCSD/CASS), A. W. Shafter (SDSU), M. J. Darnley (Liverpool JMU), A. Evans (Keele), T. J. O'Brien (Manchester), S. P. S. Eyres (Central Lancashire)
on 14 Apr 2010; 13:08 UT
Credential Certification: Michael Bode (mfb@astro.livjm.ac.uk)

Subjects: Optical, Nova

We report white light observations of the initial outburst of Nova Eridani 2009 obtained using the USAF/NASA Solar Mass Ejection Imager (SMEI) on board the Coriolis satellite. KT Eri was discovered on 2009 November 25.54 UTC at magnitude 8.1 (CBET#2050). Its outburst was then found on pre-discovery images with a peak magnitude of 5.4 on 2009 November 14.63 UT (IAUC# 9098 ) and it has subsequently been detected as a radio source (ATel#2434) and a luminous soft X-ray source (ATel#2423, ATel#2418, ATel#2392).

The Coriolis satellite is in a circular 840 km Sun-synchronous terminator orbit. SMEI consists of three baffled CCD cameras with a 60ox 3o field of view combining to sweep out a 160o arc of sky. The instrument maps out the entire sky with one orbit of the spacecraft (102 minutes) and is designed to map out large-scale variations in solar wind electron densities from Earth orbit by observing the Thompson-scattered sunlight from the heliospheric volume (B. V. Jackson et al., 2004). SMEI is operated as a high precision differential photometer and can reliably detect brightness changes down to mSMEI ~ 8. The instrument has a peak quantum efficiency at approximately 700 nm with a FWHM ~ 300 nm. The SMEI real-time data pipeline produces calibrated full sky maps in which brightness contributions from zodiacal dust and unresolved sidereal background have been subtracted (P. Hick et al., 2005).

The high cadence of SMEI along with its ability to monitor objects closer to the Sun than is often possible from the ground offers the opportunity to measure nova light curves with unprecedented temporal resolution near the peak of outburst. Here we report SMEI observations of the recent nova KT Eri through its initial rise, peak, and early decline. Photometry of KT Eri has been produced via the fitting of a modelled PSF to sky maps (P. Hick et al., 2007) between 2009 November 1.13 UT and 2009 November 30.62 UT.

The light curve, which can be found here, indicates the initial rise of the nova is steep (rising 4.1 magnitudes over 2.7 days) with evidence of a pre-maximum halt occurring on 2009 November 13.90 +/- 0.04 UT at mSMEI ~ 6. The duration of this halt would seem to be only a few hours, which is appropriate for the speed of the nova (e.g. Payne-Gaposchkin, 1964). The nova reached maximum light on 2009 November 14.67 +/- 0.04 UT with an unfiltered SMEI apparent magnitude of 5.42 +/- 0.02. It subsequently declined rapidly with a t2 value of 6.6 days confirming KT Eri as a very fast nova. The last reliable detection of the nova occurred on 2009 November 27.23 +/- 0.04 UT at mSMEI = 8.3 +/- 0.1.

The USAF/NASA SMEI is a joint project of the University of California San Diego, Boston College, the University of Birmingham (UK), and the Air Force Research Laboratory.