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A pre-outburst spectrum of KT Eri from the Digitized First Byurakan Survey (DFBS)

ATEL # 2338; Roberto Nesci (University La Sapienza, Roma, Italy), Areg Mickaelian (Byurakan Observatory, Armenia), Corinne Rossi (University La Sapienza, Roma, Italy)
on 8 Dec 2009; 0:14 UT
Password Certification: Roberto Nesci (roberto.nesci@uniroma1.it)

Subjects: Optical, Cataclysmic Variables, Nova

A historical spectrum, taken on Jan 25 1971, of the recently exploded Nova KT Eri is recorded on the plate n. 0350 of the First Byurakan Survey (FBS).

This Survey was made with a thin objective prism atop the 102/130/213 cm Schmidt telescope of the Byurakan Observatory and IIaF emulsion, covering the wavelength range 3400-6900 A. Nearly all the plates of this Survey (a.k.a Markarian Survey) have been digitized by a collaboration of the Byurakan Observatory, University La Sapienza, Rome Italy, and Cornell University (USA). The spectra in each plate were extracted with an automatic procedure and are freely accessible at the web site of the Digitized FBS (see link at bottom). More details on the DFBS can be found in Mickaelian et al. 2007, A&A 464, 1177.

A plot of the spectrum of KT Eri is given in Fig. 1 . Wavelength calibration was made using the emission lines (from H-alpha to [O II]3727) of some Planetary Nebulae in other plates of the DFBS; the reciprocal dispersion is 100 A/pixel at H-alpha, 40 A/pixel at H-beta, 22 A/pixel at H-delta and 16 A/pixel at 3700 A. The wavelength scale is linked to the spectrum using the position of the red cutoff, assumed to be at 6900 A: it may be therefore uncertain up to 3 pixels.

Ordinate of this plot is in arbitrary linear units. Crosses show the average spectral energy distribution of the G-type stars present on the plate: the double-bump shape is due to the wavelength sensitivity of the Kodak IIaF emulsion and the wavelength compression towards the red; continuous line is the spectrum on KT Eri, normalized to the G-type one.

KT Eri shows a strong UV continuum and several emission lines, indicating that it was a hot star with some circumstellar material, a situation typical of cataclismic variables and recurrent Novae. Most outstanding are the emission lines of [Ne V]3426 and [Ne III]3868 as in the case of CSS 081007:030559+054715 (ATEL #1835). Notable also a large blend around H-gamma.

The spectra of plate 0350 are slightly widened, and it helps in discriminating plate defects from spectral features: the strong dip at 4700 A is partially due to a plate defect, while all the emission lines are as wide as the continuum of the spectrum, so are most likely real. We think therefore that this star is the actual progenitor of the Nova Eri 2009.

The B and R magnitudes of the star, computed by integration of the DFBS spectrum, and tied to the zero points of the USNO-A2 catalogue, are B=14.31, R=14.22. On the USNO-A2, based on the simultaneous blue and red POSS plates of 1953-11-13, this star is reported at B=15.5, R=15.2, so it was rather blue also in 1953.

We thank John Greaves for calling our attention on this object.

Digitized First Byurakan Survey


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