BVRI photometry of ASASSN-15qi using the Tautenburg Schmidt telescope

ATel #8210; Bringfried Stecklum, Jochen Eisloeffel (Thueringer Landessternwarte Tautenburg), Alexander Scholz (University of St. Andrews)
on 23 Oct 2015; 11:44 UT
Credential Certification: Bringfried Stecklum (stecklum@tls-tautenburg.de)

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We report on photometric observations of the optical transient ASASSN-15qi performed at the Thüringer Landessternwarte Tautenburg. The brightening of this source was discovered by the All-Sky Automated Survey for Supernovae (ASAS-SN, Shappee et al. 2014, ApJ, 788, 48). The object is located west of the HII region SH2-148 and a likely member of the star forming region. Follow-up optical spectroscopy (Maehara et al., ATel #8147) revealed the presence of P-Cygni hydrogen emission lines indicating a fast wind. The spectral features point to an EX Lupi- or FU Ori-like outburst.

BVRI imaging using the 1.34m Tautenburg Schmidt telescope was performed on Oct. 11.81 using integration times of 300, 90,45, and 30s, respectively. The observations were carried out with a FOV of 42arcmin x 42arcmin at the airmass of 1.03 and the seeing of 2.3arcsec. The BV photometry was calibrated using five faint TYCHO-2 stars and the same number of stars from IPHAS (Barentsen et al. 2014) for RI. The mildly saturated cores of the TYCHO-2 stars were recovered by means of fitting Lorentzian 2D profiles to the PSFs, using non-saturated pixels only. Without this correction the apparent BV magnitudes would have been 0.12 and 0.16mag brighter, respectively. The TYCHO-2 magnitudes were transformed to the Johnson system according to the color equations from the "Tycho/Hipparcos Introduction and Guides to the Data". The following results were obtained

B=16.13±0.18, V=15.17±0.15, R=14.22±0.10, and I=13.11±0.04.

The V measurement confirms that the fading trend indicated by the ASAS-SN photometry from Oct. 2.38 (V=13.6) and 3.27 (V=13.9) continued, although at slower pace. At the date of our imaging the object was still about 2.45mag brighter in RI than during the epochs of the IPHAS observations (2004 Aug. 2.6) as well as the URAT1 photometry (2013 Apr. 18.48, Zacharias et al. 2015). Notably, the [V-R] color did not change during the outburst. Our imaging did not reveal any associated compact scattering nebula which is usually present in case of FUors (cf. Goodrich 1987). The rapid variability suggests that this object is probably of EX Lupi-type rather than being a FUor.