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Ondrejov Observations of SN 2011dh in M51 and Progenitor Implications

ATel #3433; J. L. Prieto (Carnegie Observatories), K. Hornoch (Astronomical Institute, Ondrejov)
on 15 Jun 2011; 22:39 UT
Credential Certification: Jose L. Prieto (jose@obs.carnegiescience.edu)

Subjects: Optical, Supernovae, Transient

Referred to by ATel #: 3641

Following the report of ASAS observations (ATEL #3432) of the type II supernova 2011dh in M51 (CBET #2736, ATEL #3398), here we report three epochs of V, R, and I-band imaging obtained by K. Hornoch with the 0.65-m telescope at Ondrejov, Czech Republic. Before obtaining photometric measurements, gradients in the background of M51 images were flattened using a spatial median filter. The magnitudes of the supernova were measured using aperture photometry and calibrated using a sequence of four local standards calibrated against Landolt stars. Table 1 shows the photometric measurements.

The V-band photometry reported here is consistent with the measurements presented in Arcavi et al. (ATEL #3413) and ATEL #3432. In particular, it confirms the relatively faint V-band magnitude of 14.9 in June 3.9 reached after the short duration peak reported in ATEL #3413 and ATEL #3432, and also the fast brightening (0.31 mag/day in V and 0.24 mag/day in I, between June 3.9-5.9) towards a second, much broader primary peak as was seen in the light curve of the type IIb SN 1993J (Richmond et al. 1994, AJ, 107, 1022). We note that the shorter duration of the initial light curve peak, likely produced by shock breakout emission, compared with SN 1993J (see Fig. 2), suggests a more compact progenitor star. This is consistent with the smaller inferred radius of the progenitor of SN 2011dh (ATEL #3399, #3401) compared with the progenitor of SN 1993J. From Szczygiel et al. (ATEL #3431) and Maund et al. (2011, arXiv:1106.2565) we derive a radius (assuming black-body spectrum) of R = 1.2-1.4 AU for SN 2011dh's progenitor star. In contrast, the estimated radius of the progenitor star of SN 1993J was R = 2-3 AU (Woosley et al. 1994, ApJ, 429, 300; Maund et al. 2004, Nature, 427, 129), ~2 times bigger.

We thank J. Vrastil for helping with the observations.

 
Table 1. Ondrejov 0.65-m telescope photometry of SN 2011dh 
 
    Date      Magnitude     Filter      
June 3.874  14.88 +/- 0.04    V  
June 3.868  14.51 +/- 0.03    R 
June 3.870  14.41 +/- 0.03    I 
June 4.933  14.58 +/- 0.03    V 
June 4.929  14.22 +/- 0.03    R 
June 4.940  14.19 +/- 0.03    I  
June 5.875  14.27 +/- 0.02    V 
June 5.870  13.94 +/- 0.03    R 
June 5.865  13.93 +/- 0.03    I