SN 2006dd is a bright Type Ia supernova presently visible in the galaxy NGC 1316 (Fornax A). This galaxy was also the host of supernovae 1980N and 1981D.
Meikle (2000, MNRAS, 314, 782) discusses various distance determinations to the Fornax cluster and For A in particular. He adopts a distance modulus for the cluster of m-M = 31.59 +/- 0.10 mag, equal to the surface brightness fluctuation (SBF) distance of Ferrarese et al. (2000, ApJ, 529, 745) but with a somewhat larger uncertainty. The weighted mean of the two SBF distances given by Ajhar et al. (2001, ApJ, 559, 584, Table 3) is m-M = 31.44 +/- 0.14 mag. It is this latter value that we used to calculate the absolute magnitudes of SN 1980N in our paper on the near-IR Hubble diagrams of Type Ia supernovae (Krisciunas, Phillips, and Suntzeff, 2004, ApJ, 602, L81).
The Galactic extinction along the line of sight is low, E(B-V) = 0.021 (Schlegel, Finkbeiner, and Davis 1998, ApJ, 500, 525). If SN 2006dd has a V-band absolute magnitude at maximum of -19.3, the distance modulus is 31.44 mag, if we adopt a Galactic extinction correction of 3.1 * 0.021 = 0.06 mag, and if there is zero host galaxy extinction, then the apparent magnitude of SN 2006dd at maximum would be V = 12.20.
Here is a 6 by 6 arcmin V-band image obtained with the CTIO 1.3-m telescope at 09:43 UT on 26 June 2006 (UT), with SN 2006dd and four field stars labeled. North is up and east is to the left.
Based on calibration from 5 photometric nights using observations of the Landolt (1992) field PG1657, given below are the mean magnitudes and colors for the field stars. Incidentally, the 2MASS values for "star 1" are J = 12.830 (0.022), H = 12.258 (0.023), and K = 12.135 (0.019). Calibrating it directly to Persson et al. (1998) standards (P9150, P9172, and P9109), we find it to be 0.02 to 0.06 brighter than 2MASS.
* B V R I J H K 1 16.204 0.011 15.027 0.005 14.288 0.007 13.684 0.008 12.807 0.006 12.213 0.007 12.077 0.012 2 16.180 0.005 15.567 0.007 15.203 0.008 14.858 0.008 3 16.812 0.008 15.682 0.004 14.996 0.004 14.412 0.008 4 17.470 0.008 16.859 0.006 16.489 0.007 16.114 0.006 Alternatively, for the field stars: * V B-V V-R V-I 1 15.027 1.177 0.739 1.343 2 15.567 0.613 0.364 0.709 3 15.682 1.130 0.686 1.270 4 16.859 0.611 0.370 0.745For the BVRI and JHK data shown here I have used the images themselves, night by night, as subtraction templates. This involved rotating the galaxy 180 degrees and aligning the center of the rotated galaxy with the original image. Call this the "poor man's template method". It works reasonably well on elliptical galaxies.
Optical photometry of SN 2006dd (without S-corrections)
JD- B V R I
2453000
908.90 13.570 (0.016) 13.585 (0.018) 13.461 (0.017) 13.414 (0.018)
912.91 12.682 (0.007) 12.696 (0.016) 12.624 (0.008) 12.648 (0.012)
914.90 12.500 (0.020) 12.510 (0.010) 12.442 (0.013) 12.491 (0.019)
918.89 12.348 (0.016) 12.310 (0.010) 12.319 (0.014) 12.567 (0.023)
930.88 13.062 (0.025) 12.655 (0.016) 12.753 (0.018) 13.112 (0.019)
933.88 13.388 (0.025) 12.876 (0.016) 12.905 (0.022) 13.177 (0.020)
937.86 13.919 (0.021) 13.126 (0.015) 13.001 (0.015) 13.045 (0.029)
941.89 14.425 (0.017) 13.347 (0.013) 13.056 (0.016) 12.957 (0.017)
945.88 14.871 (0.020) 13.574 (0.015) 13.178 (0.016) 12.920 (0.014)
951.86 15.273 (0.029) 13.985 (0.026) 13.595 (0.026) 13.208 (0.031)
961.79 15.631 (0.031) 14.423 (0.021) 14.114 (0.021) 13.850 (0.024)
968.83 15.748 (0.026) 14.644 (0.017) 14.383 (0.021) 14.165 (0.025)
974.82 15.885 (0.026) 14.871 (0.026) 14.711 (0.026) 14.569 (0.035)
Infrared photometry of SN 2006dd (without S-corrections)
JD- J H K
2453000
908.90 13.527 (0.015) 13.604 (0.022) 13.849 (0.086)
912.91 12.804 (0.009) 12.951 (0.031)
914.90 12.671 (0.012) 12.916 (0.012) 12.758 (0.030)
918.89 12.752 (0.014) 13.095 (0.018) 12.732 (0.058)
930.88 14.474 (0.035) 13.462 (0.020) 13.237 (0.058)
933.88 14.593 (0.027) 13.319 (0.017) 13.248 (0.055)
937.86 14.463 (0.024) 13.081 (0.016) 13.014 (0.032)
941.89 14.204 (0.022) 12.928 (0.013) 12.887 (0.018)
945.88 13.888 (0.017) 12.870 (0.012) 12.837 (0.021)
951.86 13.920 (0.023) 13.111 (0.017) 13.176 (0.049)
951.88 13.851 (0.015) 13.107 (0.012) 13.206 (0.018) ESO NTT 3.6-m
961.79 14.828 (0.034) 13.750 (0.022) 13.744 (0.039)
968.83 15.312 (0.043) 14.063 (0.025) 13.959 (0.071)
974.82 15.961 (0.084) 14.190 (0.027) 14.447 (0.090)
Next we must
correct the B-band and V-band photometry obtained with the CTIO 1.3-m
telescope and ANDICAM to the system of Bessell (1990, PASP, 102, 1181). We
must add the values derived by Krisciunas et al. (2003, AJ, 125, 166). These
are based on spectra of SNe 1999ee and 2001el. Here we show the B-band
and V-band corrections graphically:
In our paper on SN 2001el that describes the method of S-corrections (Krisciunas et al. 2003) we note that the same methodology applied to the R-band and I-band photometry actually spreads the photometry out. It does not tighten it up. So we shall just use the R-band and I-band photometry as is.
The JHK data must be corrected to the Persson et al. (1998) system using corresponding near-IR S-corrections.
Here are the S-corrections based on T(Bmax) = JD 2,453918.81. DT is corrected for time dilation using the heliocentric radial velocity of 1760 km/sec (1+z = 1.00587). DT is measured in rest frame days since T(Bmax).
DT DB DV DJ DH DK -9.85 -0.048 -0.005 0.038 0.006 -0.003 -5.87 -0.043 0.002 0.047 0.000 0.006 -3.89 -0.043 0.006 0.053 -0.005 0.013 0.08 -0.044 0.014 0.067 -0.014 0.026 12.00 -0.029 0.025 -0.028 -0.045 0.038 14.98 -0.020 0.026 -0.054 -0.045 0.025 18.94 -0.008 0.028 -0.080 -0.058 0.010 22.95 0.000 0.030 -0.096 -0.071 -0.004 26.91 -0.045 0.034 -0.051 -0.070 -0.017 32.86 -0.069 0.039 -0.091 -0.012 -0.007 42.73 -0.064 0.039 -0.131 0.033 -0.002 49.73 -0.057 0.031 -0.131 0.033 0.000 55.68 -0.049 0.025 -0.131 0.033 0.000We have applied no S-corrections for the ESO NTT 3.6-m from Aug 4 UT. Without the sizeable S-corrections for the J-band for the CTIO 1.3-m data obtained on this night, there would be a significant discrepancy, but with that S-correction, the J-band are in good agreement.
Below we see BVRI light curves of SN 2006dd made from imagery obtained from 22 June through 27 August UT. Clearly, this object was discovered long before maximum light. Such objects, especially if they have minimal host galaxy extinction, are very important for supernova research, because they allow us to get a handle on the intrinsic luminosities and colors withouth major worries due to reddening and absorption by dust.
Below we show the observed B-V colors of SN 2006dd. The dashed line in the graph is the unreddened locus of Lira (1995), based on a small number of Type Ia SNe of a wide range of decline rates. The implied total color excess in the tail of the B-V color curve is greater than 0.1 mag. This is somewhat greater than one derives from the pseudo-color Bmax - Vmax. The bottom line is that SN 2006dd has non-zero host galaxy reddening, but not a lot. The host galaxy shows evidence of having cannibalized some other galaxies. There is a dusty arc on the far south side in the optical imagery.
Given next are the near-IR JHK light curves. Note the very sharp dip in the J-band in the two weeks after J-band maximum. The data obtained with the ESO NTT 3.6-m (courtesy Valentin Ivanov) are plotted as cyan-colored triangles.
Using the multicolor light-curve shape method (MLCS2k2; Jha, Riess, and Kirshner 2006, in press), Peter Garnavich as derived the following solution for SN 2006dd using the BVRI photometry:
Time of B-band maximum = JD 2,453,918.81 +/- 0.17 MLCS Delta = +0.01 +/- 0.05 A_V (total) = 0.24 +/- 0.11 distance modulus m-M = 31.56 +/- 0.11 (on a scale of H_0 = 65 km/sec/Mpc) reduced chi-2 of fit = 12.25/48 = 0.255 R_V = 3.10 was usedUsing the value of A_V given above, it follows that A_J ~ 0.068 +/- 0.031, A_H ~ 0.043 +/- 0.020, and A_K ~ 0.028 +/- 0.013. The uncertainties of the near-IR extinction corrections are comparable or smaller than the internal errors of the IR photometry. The observed near-IR maxima are J_max ~ 12.724 +/- 0.012, H_max ~ 12.911 +/- 0.012, and K_max ~ 12.74 +/- 0.04. Adopting the SBF distance modulus of Ajhar et al. (2001), we obtain absolute magnitudes of M_J = -18.78 +/- 0.14, M_H = -18.57 +/- 0.14, M_K = -18.73 +/- 0.15. These values are somewhat brighter than the mean values given in Table 17 of Krisciunas et al. (2004, AJ, 128, 3034), namely M_J = -18.61, M_H = -18.44, and M_K = -18.44.
Let us set aside any discussion of the true distance modulus of NGC 1316 and SN 2006dd and compare the extinction-corrected JHK maxima of SNe 1980N (Krisciunas, Suntzeff, and Phillips, 2004, Table 1) and 2006dd:
SN 1980N SN 2006dd difference
J_corr 12.78 (0.08) 12.66 (0.03) 0.12 (0.09)
H_corr 13.20 (0.10) 12.87 (0.02) 0.33 (0.10)
K_corr 13.08 (0.10) 12.71 (0.04) 0.37 (0.11)
Since these two SNe occurred in the same galaxy, they must effectively be at
the same distance. Though the host has some dust, neither SN is high-reddened. So
the extinction-corrected maximum magnitudes must give a measure of the
intrinsic luminosity difference of the two objects. SN 2006dd was
clearly brighter, in H and K at least. These are 3.2-sigma and 3.4-sigma
differences in H and K.It should be noted that SN 1980N was not observed in the near-IR overlapping the time of the IR maxima. We used JHK templates to estimate what those maxima were. SN 2006dd had minima at ~two weeks after T(Bmax) where were deeper than other SNe we have studied. Had we observed SN 2006dd starting 5 days after T(Bmax) and used our JHK templates to estimate the JHK maxima, we would have obtain values which would be "too faint".
An obvious thing to do would be to compare the entire IR light curves of SN 2006dd with those of SNe 1980N and 1981D (Elias et al. 1981, ApJ, 251, L81).
This page was last updated on September 1, 2006.
Kevin Krisciunas
Univ. of Notre Dame
[and Cerro Tololo Obs.]
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