Spectroscopic and photometric follow-up of OGLE-2015-NOVA-01
ATel #7472; P. Mroz, L. Wyrzykowski (Warsaw University Observatory), E. Aydi, P. A. Whitelock (SAAO, UCT), T. Nagayama (Kagoshima University), M. Dominik, A. Scholz (St. Andrews), S. T. Hodgkin (IoA Cambridge), S. Nishiyama, A. Iwamatsu, I. Kawamata (Miyagi University of Education), A. Smith (NCAC), M. Litwicki
on 5 May 2015; 09:21 UT
Credential Certification: Przemek Mroz (pmroz@astrouw.edu.pl)
Subjects: Infra-Red, Optical, Cataclysmic Variable, Nova, Transient
We report SALT/RSS observations of the transient OGLE-2015-NOVA-01 (ATel #7179, ATel #7394). We obtained the spectrum covering a range of 445-710 nm with a resolution R ~ 9000. It was collected on 2015 April 22/23, i.e. 55 days after the onset of the outburst. The spectrum shows a red continuum with a prominent, broad H-alpha in emission (FWHM~1810+/-20 km/s). There are some additional weak, broad emission lines of H-beta, Fe II, and N II.
We also obtained a multicolor photometry using LCOGT 1-m robotic telescopes, on 2015 April 22-23. Observations are summarized in the table below.
JD Exp. time [s] Filter Brightness [mag]
2457134.54210 200.0 g 18.552 +/- 0.054
2457134.54495 100.0 i 14.545 +/- 0.017
2457134.54692 100.0 r 15.751 +/- 0.022
2457134.56704 200.0 g 18.405 +/- 0.033
2457134.60383 200.0 g 18.468 +/- 0.043
2457134.60668 100.0 i 14.513 +/- 0.029
2457134.60844 100.0 r 15.749 +/- 0.028
2457134.64641 200.0 g 18.365 +/- 0.065
2457134.64937 100.0 i 14.499 +/- 0.028
2457134.65112 100.0 r 15.712 +/- 0.033
2457135.49224 100.0 i 14.858 +/- 0.035
2457135.52519 200.0 g 18.598 +/- 0.040
2457135.52787 100.0 i 14.739 +/- 0.049
2457135.52974 100.0 r 15.870 +/- 0.024
2457136.41575 100.0 i 14.462 +/- 0.053
2457136.41738 100.0 r 15.712 +/- 0.056
(g-r) and (r-i) colors practically has not changed compared to the previous LCOGT observations on 2015 March 19 (ATel #7394).
We obtained a near-infrared photometry from the IRSF, Sutherland, South Africa:
JD J H Ks
2457134.524 11.2 10.4 9.8
2457137.500 10.5 9.6 9.1
2457138.465 10.7 9.7 9.2
2457139.553 10.5 9.6 9.1
2457140.408 10.5 9.6 9.1
The uncertainty of measurements is 0.1 mag. The J,H,Ks brightness variations are consistent with the OGLE I-band light curve of OGLE-2015-NOVA-01 (ATel #7394). It shows semi-regular variations with an amplitude of 1 mag and a timescale of 11 d.
The star might be an exceptionally slow classical nova (V849 Oph and V992 Sco showed similar long, flat maxima; see Fig. 7 and 15 of Strope et al. 2010). The eruption of a symbiotic nova is unlikely, given the brightness of the progenitor. Another explanation might be a red nova. Eruptions of red novae have light curves resembling that of OGLE-2015-NOVA-01, showing significant variations on a time-scale of months. We are unable to discriminate between these scenarios with the available data.
The SALT/RSS observations were carried out under the DDT program number 2014-2-DDT-006. LCOGT observations were carried under proposal STA2015A-003 to M. Dominik.
