Peremennye Zvezdy (Variable Stars) 26, No. 3, 2006 Received 27 February; accepted 25 March.

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Photometric observations of Supernovae 2000E, 2001B, 2001V, and 2001X

D. Yu. Tsvetkov

Sternberg Astronomical Institute, 13, University Ave., Moscow 119992, Russia, e-mail: tsvetkov@sai.msu.su

Introduction

Continuing the long-term program of supernova (SN) observations at Sternberg Astronomical Institute, we carried out photometry of bright SNe 2000E, 2001B, 2001V, and 2001X.

SN 2000E was discovered by Valentini et al. (2000) at magnitude =14.3 on CCD images obtained with the Teramo 0.72-m TNT telescope on January 26.73 UT. SN was located at (equinox 2000.0), which is west and south of the center of the Sbc galaxy NGC 6951. Turatto et al. (2000) reported that spectra obtained with the 1.8-m telescope at Cima Ekar on January 27.83 UT indicated that SN 2000E was a type Ia event, few days before maximum light. CCD photometry of this SN was reported by Vinko et al. (2001) and Valentini et al. (2003).

The discovery of SN 2001B was reported by Xu and Qiu (2001) on behalf of Beijing Astronomical Observatory SN survey on January 3.61 UT at magnitude 15.5, estimated from an unfiltered CCD image. The SN was located at (equinox 2000.0), which is west and south of the nucleus of the Sc galaxy IC 391. Chornock and Filippenko (2001) reported that spectra of SN 2001B, obtained on January 23 with the Shane 3-m reflector at Lick Observatory, revealed that the object was probably a type Ib SN, roughly one week past maximum brightness.

SN 2001V was discovered by P. Berlind on February 19.38 UT with the F.L. Whipple Observatory's 1.5-m telescope (Jha et al., 2001). The following precise position was determined for SN 2001V: (equinox 2000.0), which is east and north of the nucleus of the edge-on Sb galaxy NGC 3987. The spectrum of the SN exhibited a blue continuum with broad features, identifying this as a type Ia SN well before maximum light. Photometry of SN 2001V was later reported by Vinko et al. (2003).

The discovery of SN 2001X was reported by Li et al. (2001) on behalf of Beijing Astronomical Observatory SN survey. The object was found (magnitude about 17.0) on an unfiltered image taken with the BAO 0.6-m telescope on February 27.8 UT. SN 2001X was located at (equinox 2000.0), which is west and south of the nucleus of the Sbc galaxy NGC 5921. Chornock et al. (2001) reported that a spectrum of SN 2001X, obtained with the Lick Observatory Shane 3-m telescope on March 3.5 UT under poor conditions, showed a very blue continuum with strong H Balmer lines, indicating that it was a type-II SN before maximum light.

Observations and reductions

Our observations were carried out with the 60-cm reflector of Crimean Observatory of Sternberg Astronomical Institute (C60) using a SBIG ST-7 CCD camera and with the 30-cm refractor (M30) and 70-cm reflector (M70), both having SBIG ST-6 cameras, in Moscow. All reductions and photometry were made using IRAF.¹

The color terms for transformation of instrumental magnitudes to standard were determined for different observing seasons and telescope-filter-detector combinations using observations of standards in M 67 (Chevalier and Ilovaisky, 1991) and in NGC 7790 (Stetson, 2000). The equations were solved for color terms, which are listed in Table 1. The images of the SNe with comparison stars are shown in Figs. 1-4. The magnitudes of comparison stars were determined on photometric nights, when we observed standards from Landolt (1992) and standard regions in the clusters M 67, NGC 7790, and M 92 (http://cadcwww.hia.nrc.ca/cadcbin/wdb/astrocat/stetson/query/NGC6341).
Some magnitude estimates for comparison stars were obtained during observations of SNe, but they were verified later, in 2002-2004, using observations with C60 and M70 equipped with CCD cameras Apogee AP-7p and Ap-47p; Roper Scientific VersArray1300B. Final values for magnitudes of comparison stars were determined by averaging data from 5-8 nights; they are presented in Table 2, where the designations of stars consist of the galaxy name and the star number on the chart.

Photometric measurements of the SNe were made relative to comparison stars using PSF-fitting with IRAF DAOPHOT package. The background of host galaxies around SNe was quite smooth in most cases, which was not surprising, taking into account high focal ratios of our telescopes. Subtraction of images of host galaxies, obtained when SNe were no longer detectable, was applied in some cases for SNe 2001B and 2001X, and the results were found virtually identical to those obtained without subtraction. The results of SNe observations are presented in Tables 3-6, and the light curves are shown in Figs. 5-8.

Results and conclusions

SN 2000E. The light curves are shown in Fig. 5. They appear typical for SN Ia, the data are in a good agreement with the template light curves of SN Ia 1991T (Lira et al., 1998), except that the decline rate at late stages for SN 2000E is higher than for SN 1991T. Our magnitudes are in a good agreement with the results of Valentini et al. (2003) and Vinko et al. (2001). However, our magnitude of comparison star 1 differs significantly from the value given by Vinko et al. (2001): . The magnitudes of the SN at maximum light and at the inflection point can be determined: on JD 2451577, on JD 2451579, on JD 2451577, on JD 2451575, on JD 2451607. SN 2000E had quite slow decline past maximum: , mag/day, , but the rate of decline after the inflection point was close to the mean values for SNe Ia: .

SN 2000E clearly suffered significant extinction both in our Galaxy and in the host galaxy. The Galactic extinction in the direction of NGC 6951 is according to Schlegel et al. (1998), but Burstein and Heiles (1982) gave a much smaller value, . Valentini et al. (2003) reported that the interstellar NaI D lines in the spectrum of SN 2000E, which originated in the host galaxy, had the equivalent width EW(NaI) 0.6 Å. According to Turatto et al. (2003), this value of EW(NaI) may correspond to color excess from 01 to 03. So, using these data, we can estimate the total reddening of SN 2000E to lie between 0.32 and 0.70. Comparing the color curve of SN 2000E with the color curves for SNe Ia with negligible extinction in host galaxies, we can estimate . Valentini et al. (2003) adopted as the most likely value, after considering different methods for its determination. If we take this value for reddening and the distance modulus from LEDA (http://leda.univ-lyon1.fr/), which was computed using the radial velocity of the host galaxy, corrected for Virgocentric flow, and km sMpc, then we obtain for the absolute magnitude of SN 2000E . This is clearly brighter than the average value for SNe Ia and confirms the relation between rate of decline and absolute magnitude for SNe Ia (Pskovskii, 1977, Phillips, 2005).

SN 2001B. The light curves are shown in Fig. 6, where we also plotted the data reported by amateur astronomers at
http://www.astrosurf.com/snweb2/2001/01B_/01B_Meas.htm. Their results are in satisfactory agreement with our data, and we can assume that the peak of -band light curve is correctly determined by observations of amateurs. Supposing the light curve had the same shape of the peak, we fitted it to the -band light curve of SN Ib 1983N (Cappellaro et al., 1995), and the agreement seems quite satisfactory. We can estimate the magnitudes at maximum light: on JD 2451929, on approximately the same date. The rate of linear decline after the inflection point was mag/day both in and bands. It is difficult to estimate extinction in the host galaxy for SN 2001B because color curves of type Ib/c SNe have considerable scatter. However, in this case we can suppose that it was not large, because reports on spectroscopic observations did not mention noticeable NaI interstellar lines and the color near maximum was quite blue: . Adopting the distance from LEDA and Galactic extinction from Schlegel et al. (1998), we derive , which is close to the mean value for SN Ib/c (Richardson et al., 2002)

SN 2001V. The light curves, presented in Fig. 7, can be matched closely by those for SN 1991T. Our data are in a good agreement with the results by Vinko et al. (2003), only in the band some systematic difference can be noticed. Our magnitudes for comparison star 1 are in excellent agreement with data by Vinko et al. (2003), with maximum difference of only 001. The magnitudes at maximum light can be determined from template curve fitting, as there was a gap in observations near maximum: . The time of maximum in was about JD 2451974. SN 2001V was clearly a slowly declining SN Ia, but as the maximum was not covered with observations, we do not attempt to derive but estimate only . This value is similar to that for SN 2000E. The extinction for SN 2001V is very small both in our Galaxy and in the host galaxy: Galactic according to Schlegel et al. (1998), and the color curve does not show any significant reddening. Vinko et al. (2003) derived the total reddening . Adopting this value and the distance modulus from LEDA, we obtain - the same values as for SN 2000E. Thus, the photometric characteristics of these two SNe Ia are nearly identical.

SN 2001X. This SN was certainly a type II-P event, as can be seen from Fig. 8, where we also plotted data obtained by amateur astronomers in the bands close to and from http://www.astrosurf.com/snweb2/2001/01X_/01X_Meas.htm. Most of their magnitudes are in good agreement with our results. The light curves are fitted with those for the typical SN II-P 1999gi (Leonard et al., 2002). We can estimate on JD 2451974, . The plateau phase lasted approximately until JD 2452077, that is about 103 days, which is a quite typical value for type II-P SNe. The Galactic extinction in the direction of SN 2001X amounts to according to Schlegel et al. (1998). Comparison of the color curve for SN 2001X with that for SN 1999gi allows us to conclude that the reddening of SN 2001X in the host galaxy was negligible. Adopting from LEDA, we estimate , close to the mean value for SN II-P (Richardson et al., 2002).

The results of our study show that all the studied SNe are typical for their classes considering the shape of their light curves and their absolute magnitudes at maximum.

Acknowledgements: This research made use of the Lyon-Meudon Extragalactic Database (LEDA) and of the Canadian Astronomy Data Centre. The author is grateful to V.P. Goranskij, S.Yu. Shugarov, and I.M. Volkov for help in the observations. The work was partly supported by grant 05-02-17480 from the Russian Foundation for Basic Research.

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Footnotes

... IRAF.¹

IRAF is distributed by the National Optical Astronomy Observatory, which is operated by AURA under cooperative agreement with the National Science Foundation

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