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Peremennye Zvezdy (Variable Stars) 45, No. 12, 2025 Received 7 October; accepted 15 October. |
Article in PDF |
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DOI: 10.24412/2221-0474-2025-45-110-114
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The Light Curves of Type Ia Supernova 2016coj
D. Yu. Tsvetkov1, N. N. Pavlyuk1, I. M. Volkov1, S. Yu. Shugarov1,2, S. V. Zhuiko1
- M.V.Lomonosov Moscow State University, Sternberg
Astronomical Institute, Universitetskii pr.13, 119234 Moscow,
Russia
- Astronomical Institute of Slovak Academy of Sciences, Tatranska Lomnica, 05960, Slovakia
Photometric observations of SN Ia 2016coj spanning the
time interval from -10 to 165 days with respect to the  -band
maximum are reported. SN2016coj occurred in an elliptical
galaxy, and our results confirm negligible host galaxy extinction.
We determine basic photometric parameters and show that
SN2016coj exhibits normal photometric evolution for objects of
this class. The distance estimates to the host galaxy, derived
using the relations between luminosity and photometric parameters
of SN2016coj, are consistent with independent results.
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1. Introduction
Type Ia Supernovae (SNe Ia) are used as standardizable candles for establishing the distance scale in the Universe; their luminosity is correlated with the light curve shape (Pskovskii 1977, Phillips 1993). Despite the importance of SNe Ia, the nature of their progenitors and explosion mechanism remain a subject of discussion. Interstellar extinction is one of the main factors preventing exact determination of photometric parameters of SNe and their internal scatter. The studies of SNe Ia that are supposed to have negligible extinction in their host galaxies may provide clues to these problems. SN2016coj, which occurred in an elliptical galaxy, belongs to such objects.
SN2016coj was discovered by the Lick Observatory Supernova
Search (Filippenko et al. 2001) in an unfiltered Katzman Automatic
Imaging Telescope (KAIT) image taken on 2016 May 28.194 UT, at
. The coordinates were measured to be
(Zheng et
al. 2017). SN2016coj is
east and
north of
the nucleus of the host galaxy NGC 4125, which has the redshift 
according to the NASA/IPAC Extragalactic Database
(NED)1. It is an early-type
peculiar elliptical galaxy, morphological type E6 pec (de
Vaucouleurs et al. 1991).
SN 2016coj was detected in a KAIT prediscovery image taken on May
24.188 UT with an unfiltered magnitude
. In
addition, an unfiltered prediscovery detection was made on May
23.909 UT by R. Arbour with a 0.35-m reflector, at brightness
(Zheng at al. 2017).
Two classification spectra of SN 2016coj were obtained shortly after the SN had been discovered. The spectra were taken with the Kast double spectrograph at the Shane 3-m telescope of Lick Observatory and the FLOYDS robotic spectrograph at the Las Cumbres Observatory Global Telescope Network 2.0-m Faulkes Telescope North (in Haleakala, Hawaii). The spectra show absorption features from ions typically seen in SNe Ia including CaII, SiII, FeII, MgII, SII, and OI (Zheng et al. 2017).
photometry of SN2016coj was reported by Richmond and
Vietje (2017), Stahl et al. (2019). Zheng et al. (2017) presented
unfiltered photometry and a spectral sequence covering about a
month of evolution.
2. Observations and data reduction
Photometric CCD observations of SN2016coj in the 
bands
started immediately after its discovery, on May 29, they were
performed with the 60-cm telescope (C60) of the Crimean
Astronomical Station of Sternberg Astronomical Institute (SAI
CAS), the 1-m telescope (S100) of Simeiz Observatory (Nikolenko et
al. 2019), the 60-cm and 18-cm telescopes (L60, L18) of Stara
Lesna Observatory of the Institute of Astronomy in Slovakia, the
70-cm and 20-cm telescopes (M70, M20) of SAI Moscow observatory.
Standard image reductions and photometry were performed using IRAF2. Photometric measurements of the SN were made relative to local standard stars using PSF fitting with the IRAF DAOPHOT package. The galaxy background was subtracted using images of the host galaxy obtained at the 70-cm telescope two years after the discovery of the SN.
The image of SN2016coj and local standard stars is presented in Fig. 1. The stars were calibrated using Gaia synthetic photometry3.
The photometry is reported in the Table.
Table. photometry of SN2016coj
JD 2457000 |
 |
|
 |
 |
 |
Telescope |
| 538.31 | 14.50 (0.11) | 14.60 (0.03) | 14.56 (0.03) | 14.37 (0.03) | 14.30 (0.03) | M70 |
| 540.35 | 13.77 (0.04) | 13.94 (0.01) | 13.96 (0.02) | 13.79 (0.02) | 13.74 (0.02) | M70 |
| 545.42 | 12.91 (0.04) | 13.27 (0.02) | 13.32 (0.04) | 13.39 (0.02) | L60 | |
| 546.41 | 13.20 (0.02) | 13.18 (0.03) | 13.14 (0.02) | 13.39 (0.02) | L18 | |
| 550.30 | 13.19 (0.05) | 13.13 (0.02) | 13.08 (0.02) | 13.48 (0.03) | S100 | |
| 553.34 | 13.35 (0.03) | 13.21 (0.03) | 13.18 (0.03) | 13.58 (0.06) | S100 | |
| 553.33 | 13.45 (0.03) | 13.14 (0.03) | 13.20 (0.02) | M20 | ||
| 554.30 | 13.42 (0.06) | 13.23 (0.02) | 13.26 (0.02) | 13.68 (0.02) | S100 | |
| 557.29 | 13.75 (0.04) | 13.42 (0.02) | 13.57 (0.02) | 13.91 (0.02) | S100 | |
| 557.50 | 13.72 (0.04) | 13.80 (0.02) | 13.49 (0.02) | 13.58 (0.02) | 13.88 (0.02) | L60 |
| 558.30 | 13.88 (0.03) | 13.51 (0.03) | 13.66 (0.02) | 13.96 (0.02) | S100 | |
| 560.30 | 14.12 (0.02) | 13.63 (0.02) | 13.75 (0.01) | 13.97 (0.02) | S100 | |
| 562.36 | 14.54 (0.05) | 13.68 (0.03) | 13.74 (0.03) | M20 | ||
| 564.29 | 14.70 (0.02) | 13.86 (0.02) | 13.70 (0.13) | 13.82 (0.01) | S100 | |
| 566.30 | 14.98 (0.03) | 14.00 (0.02) | 13.82 (0.02) | 13.74 (0.02) | S100 | |
| 568.40 | 15.18 (0.04) | 14.20 (0.03) | 13.77 (0.02) | 13.61 (0.03) | L18 | |
| 570.40 | 15.52 (0.07) | 14.23 (0.04) | 13.91 (0.02) | M20 | ||
| 576.49 | 16.08 (0.03) | 14.83 (0.03) | 14.54 (0.03) | 14.08 (0.03) | C60 | |
| 582.28 | 16.28 (0.03) | 15.07 (0.02) | 14.82 (0.02) | 14.46 (0.03) | C60 | |
| 603.36 | 16.64 (0.03) | 15.79 (0.03) | 15.53 (0.02) | 15.48 (0.02) | L60 | |
| 630.32 | 17.05 (0.04) | 16.59 (0.03) | 16.53 (0.03) | 16.59 (0.06) | C60 | |
| 631.30 | 17.02 (0.09) | 16.59 (0.07) | 16.57 (0.04) | 16.65 (0.07) | C60 | |
| 634.23 | 17.05 (0.04) | 16.67 (0.03) | 16.62 (0.03) | 16.66 (0.05) | C60 | |
| 637.29 | 17.09 (0.05) | 16.65 (0.04) | 16.65 (0.03) | 16.77 (0.05) | C60 | |
| 646.30 | 17.18 (0.07) | 16.92 (0.05) | 16.99 (0.04) | 16.94 (0.07) | C60 | |
| 704.54 | 18.13 (0.09) | 18.05 (0.05) | 18.30 (0.05) | 17.85 (0.09) | C60 | |
| 711.54 | 18.41 (0.04) | 18.36 (0.06) | 18.56 (0.05) | 17.96 (0.10) | C60 | |
| 713.53 | 18.43 (0.05) | 18.36 (0.09) | 18.53 (0.06) | C60 |
3. The light and color curves
The light curves of SN2016coj are presented in Fig. 2.
 |
Fig. 2.
The light curves of SN2016coj in the |
Our data are in a good agreement with the results by Stahl et al.
(2019). The magnitudes from Richmond and Vietje (2017) agree with
our data at the epoch near maximum, but at later phases, show
systematic errors that reach about
for the band near
JD2457600. The combined data of three sets of observations allow
us to determine the epochs and magnitides of maximum light in
different passbands. The maximum in the band was reached at
with
. The magnitudes and time
differences with respect to
for the 
bands are, respectively, 12
75, 0
; 1314,
+1
5; 1308, +17; 1335, -20. The
uncertainties of the data for the -band maximum are about
15, 2, while for other bands, they are
,
15. The first light epoch was determined by Zheng et al.
(2017): JD2457531.8
0.5, so the rise time is 165, which
is slightly less than the mean value of 18 days for SNe Ia. For
the decline rate parameter, identical values were found by Stahl
et al. (2019) and Richmond and Vietje (2017):
; our data confirm this conclusion. The decline
rates at late phases in the 
bands are,
respectively, 0.017, 0.021, 0.024, 0.016 magday
.
The light curves of SN2002er, which has an identical decline
rate parameter 
= 1.33 (Pignata et al. 2004,
Ganeshalingam et al. 2010), are compared to those for SN2016coj.
The light curves of these two SNe Ia are similar, some differences
may be noted near the second maximum on the -band light curve
and at the final decline phase on the - and -band light
curves.
The color curves for SN2016coj are presented in Fig. 3 and
compared to those for SN2002er. The shapes of the color curves
are generally similar for both SNe in all colors. Some differences
may be noted at the early phases, when SN2016coj is bluer, and
at the final decline stage, when it is redder. The color curves of
SN2002er were shifted by the amount corresponding to
. The total reddening for SN2002er was estimated
as
(Pignata et al. 2004); for
SN2016coj, the Galactic extinction is
(Shlafly
& Finkbeiner 2011), so the comparison of the color curves
confirms negligible extinction in the host galaxy of SN2016coj.
 |
Fig. 3. The color curves of SN2016coj. The symbols are the same as in Fig. 2. Red lines show the color curves of SN2002er. |
4. The distance and absolute magnitude
Calibration of the width-luminosity relation (WLR) by Prieto et
al. (2006) gives
. Another calibration is based on
the color stretch parameter 
(Ashall et al. 2020). We
determined
; the relation from Ashall et al.
(2020) gives nearly the same result
, which
corresponds to the distance modulus
. The
uncertainty of this estimate is mainly due to dispersions of the
calibrating relations, which are about
(Prieto
et al. 2006, Ashall et al. 2020). We can compare this distance
estimate with independent data for the host galaxy NGC4125. The
Distance-Velocity Calculator4 returns the distance 23.22 Mpc,
corresponding to
. The Surface Brightness
Fluctuation (SBF) method gives
(Tully et
al. 2013), in good agreement with the previous estimate. Taking
into account the dispersion of the calibrating equations for SNe
Ia, the distance determined from SN2016coj data is consistent
with independent estimates. We cannot exclude that SN2016coj is
about
fainter that predicted by the calibration, as such
deviations are within the scatter of the WLR.
Acknowledgements. The study was conducted under the state
assignment of Lomonosov Moscow State University.
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