BVRI photometric evolution of the very fast Nova Ophiuchi 2010 N.1 = V2673 Oph
aa r X i v : . [ a s t r o - ph . S R ] M a r COMMISSIONS 27 AND 42 OF THE IAUINFORMATION BULLETIN ON VARIABLE STARS
Number 5932 Konkoly ObservatoryBudapest26 March 2010
HU ISSN 0374 – 0676
BVR C I C PHOTOMETRIC EVOLUTION OF THE VERY FASTNOVA OPHIUCHI 2010 N.1 = V2673 OPH
U. MUNARI , S. DALLAPORTA INAF Osservatorio Astronomico di Padova, Sede di Asiago, I-36032 Asiago (VI), Italy ANS Collaboration, c/o Astronomical Observatory, 36012 Asiago (VI), Italy
Nova Ophiuchi 2010 N.1 (= V2673 Oph) was discovered by H. Nishimura on Jan. 15.9UT (cf. Nakano 2010) and confirmed spectroscopically by H. Maehara (2010) as a ”FeII” class nova.We obtained
BV R C I C photometry of Nova Ophiuchi 2010 N.1 with a 0.30-m MeadeRCX-400 f/8 Schmidt-Cassegrain telescope equipped with a SBIG ST-9 CCD camera.The photometry was accurately corrected for color equations using nightly calibrationson Landolt (1992, 2009) standard stars. The data are presented in Table 1, and plotted inFigure 1. The combined (Poissonian + transformation) errors (always less than 0.03 mag)do not exceed the dimension of the symbols in Figure 1. The zero points of the photometryare scaled on the nearby star TYC 6260-1846-1, for which we adopted: B =11.550, V =10.963, R C = 10.574 and I C = 10.222. The B and V are the values recommended byAAVSO for this star, the R C and I C are derived combining B , V with J , H , K from2MASS following the recipes by Caldwell et al. (1993).We started our observations immediately past maximum, and thus to reconstruct thewhole lightcurve as presented in Figure 1, we had to integrate them with the publisheddata.Various estimates, based on unfiltered CCD observations secured around the time ofdiscovery with digital cameras by Japanese amateurs, were published in CBET 2128.These observations are generally calibrated against the R C band values of field stars aslisted by the USNO catalog. We have measured the field stars around Nova Ophiuchi2010 N.1 and found a mean
IBVS V band data by VSNET observer H. Maehara. The B , R C and I C data of the latter, however,need the application of a shift to be brought in agreement with the rest of the data. Theshift we applied amounts to +0.32 mag in B , +0.34 in R C , and +0.45 mag in I C .Table 1. Our BV R C I C of Nova Oph 2010 N.1HJD V B − V V − R C V − I C V =8.5. At that time the colors were B − V =+0.95, V − R C =+0.75, and V − I C =+1.50.van den Bergh and Younger (1987) derived a mean intrinsic color ( B − V ) ◦ =+0.23 ± B − V ) ◦ = − ± t . Comparingwith B − V =+0.95 at maximum and B − V =+0.68 at t from Figure 1, the reddeningaffecting Nova Oph 2010 N.1 is E B − V =0.71, and the extinction (assuming a standard R V =3.1 interstellar law) is therefore A V =2.2 mag.The light-curve in Figure 1 is characterized by a rapid rise (the last 2.2 mag in V bandwere covered in 3.4 days) and by a smooth decline, regulated by the decline times t V = 10 . t V = 23 . V band, by two and three mag-nitudes, respectively, from maximum brightness. These t V and t V values for Nova Oph2010 are in the normal proportion found for typical novae. Given t V , the Warner (1995)relation would predict t V =20.8, while Munari et al. (2008) relation would give t V =23.1.According to the classification of Warner (1995, his Table 5.4), a t V = 10 days qualifiesNova Oph 2010 N.1 to be classed among the very fast novae.Published relations between the absolute magnitude and the rate of decline generallytake the form M max = α n log t n + β n . Using the Cohen (1988) V - t relation, the distanceto the nova is 8.3 kpc, and 7.5 kpc according to the Schmidt (1957) V - t relation. BVS Figure 1.
BV R C I C photometric evolution of the outburst of Nova Ophiuchi 2010 N.1. For theliterature data, see text for details. IBVS
Buscombe and de Vaucouleurs (1955) suggested that all novae have the same absolutemagnitude 15 days after maximum light. The mean value of the calibrations presentedby Buscombe and de Vaucouleurs (1955), Cohen (1985), van den Bergh and Younger(1987), van den Bergh (1988), and Capaccioli et al. (1989) is M V = − ± V =10.85 fromFigure 1. Taking the mean of these three determinations, the distance to Nova Oph 2010N.1 is d =7.4 kpc. At a galactic latitude b =4.92 deg, it corresponds to an height over theGalactic equatorial plane of zz