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Optical Spectrum of the NGC 2770 Transient

ATEL # 1358; J. R. Thorstensen (Dartmouth)
on 13 Jan 2008; 3:31 UT
Password Certification: J. R. Thorstensen (john.thorstensen@dartmouth.edu)

Subjects: Optical, X-ray, Nova, Supernova, Transients

I have obtained a spectrum of the apparent optical counterpart of the X-ray transient in NGC 2770 (ATel 1353, 1354, 1355, and 1356), using the 2.4-m Hiltner telescope at MDM Observatory on Kitt Peak. There were 5 exposures of 10 minutes each, centered around 2008 January 12.32 UT. The modular spectrograph gave 3.5 Angstrom resolution from 4300 to 7500 A, with vignetting toward the ends. The spectrum shows a strong, smooth continuum. The only spectral features clearly detected are (a) sharp, Na D absorption, at cz = 2100 km/s, with a combined equivalent width of about 1 Angstrom; and (b) sharp H-alpha emission, also at 2100 km/s, with an emission EW of about 5 Angstrom. The background shows strong emission at H-alpha from the galaxy, and the H-alpha in the transient object's spectrum could be poorly subtracted background. The redshifts of the features are consistent with that of NGC 2770 (listed as 1947 km/s in the NED), given that the source is located toward the outskirts of the galaxy where the rotation should be large. The spectrum does not offer a definitive answer as to what kind of object this is, but the redshifted NaD absorption puts it at least as distant as NGC 2770.


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