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On the Pre-nova Optical Brightness of V2491 Cyg

ATel #1504; S. Balman, Y. Pekon, U., Kiziloglu (METU)
on 2 May 2008; 12:42 UT
Credential Certification: Solen Balman (solen@astroa.physics.metu.edu.tr)

Subjects: Optical, Binary, Cataclysmic Variable, Nova, Transient, Variables

We report on the pre-nova optical observations of the fast nova V2491 Cyg (IAUC 8934 , CBET 1334, ATEL #1473, #1475, #1478, #1480, #1485). The location of the pre-nova was serendipitiously observed with the ROTSE IIId telescope (Akerlof et al. 2003, PASP, 115, 132) on Bakirlitepe, TUBITAK National Observatory, Turkey, starting in July 2007 until end of November 2007. A total of 585 frames (unfiltered), each 5 sec, have been taken that include the vicinity of the nova. We performed photometric analysis on the calibrated and combined images in order to detect and derive the brightness of the pre-nova source. For the analysis MIDAS and DAOPHOT software package have been used and magnitude calibrations were made using several USNO-B1 catalogue stars and their R band magnitudes. We combined 18 frames with best seeing conditions for each month of August, September and October 2007 resulting a total image of 90 sec for each month. Finally, all images were combined to a one 4.5 min exposure image for analysis. As a result, we do not find a pre-nova optical source or candidate in any of our single or combined images tracing back to 5-9 months prior to outburst of this source given the position and position error noted in ATEL #1473 and #1478 . We list our 2sigma frame upper limits as: 18.2+/-0.5 for 09-19 Aug. 2007; 18.0+/-0.5 for 03-12 Sept. 2007; and 18.0+/-0.5 for 06-11 Oct. 2007. The frame upper limit at the 2sigma level for the total 4.5 min exposure is 18.6+/-0.5 (Photometric calibrated R band magnitude).