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Register a new userASASSN-14dq: A fast-declining type II-P Supernova in a low-luminosity host galaxy
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Optical broadband (UBVRI) photometric and low-resolution spectroscopic observations of the type II-P supernova (SN) ASASSN-14dq are presented. ASASSN-14dq exploded in a low-luminosity/metallicity host galaxy UGC 11860, the signatures of which are present as weak iron lines in the photospheric phase spectra. The SN has a plateau duration of $sim,$90 d, with a plateau decline rate of 1.38 $rm mag (100 d)^{-1}$ in V-band which is higher than most type II-P SNe. ASASSN-14dq is a luminous type II-P SN with a peak $V$-band absolute magnitude of -17.7$,pm,$0.2 mag. The light curve of ASASSN-14dq indicates it to be a fast-declining type II-P SN, making it a transitional event between the type II-P and II-L SNe. The empirical relation between the steepness parameter and $rm ^{56}Ni$ mass for type II SNe was rebuilt with the help of well-sampled light curves from the literature. A $rm ^{56}Ni$ mass of $sim,$0.029 M$_{odot}$ was estimated for ASASSN-14dq, which is slightly lower than the expected $rm ^{56}Ni$ mass for a luminous type II-P SN. Using analytical light curve modelling, a progenitor radius of $rm sim3.6times10^{13}$ cm, an ejecta mass of $rm sim10 M_{odot}$ and a total energy of $rm sim,1.8times 10^{51}$ ergs was estimated for this event. The photospheric velocity evolution of ASASSN-14dq resembles a type II-P SN, but the Balmer features (H$alpha$ and H$beta$) show relatively slow velocity evolution. The high-velocity H$alpha$ feature in the plateau phase, the asymmetric H$alpha$ emission line profile in the nebular phase and the inferred outburst parameters indicate an interaction of the SN ejecta with the circumstellar material (CSM).
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We present high-cadence, comprehensive data on the nearby ($Dsimeq33,rm{Mpc}$) Type II SN 2017ahn, discovered within $sim$1 day of explosion, from the very early phases after explosion to the nebular phase. The observables of SN 2017ahn show a significant evolution over the $simeq470,rm{d}$ of our follow-up campaign, first showing prominent, narrow Balmer lines and other high-ionization features purely in emission (i.e. flash spectroscopy features), which progressively fade and lead to a spectroscopic evolution similar to that of more canonical Type II supernovae. Over the same period, the decline of the light curves in all bands is fast, resembling the photometric evolution of linearly declining H-rich core-collapse supernovae. The modeling of the light curves and early flash spectra suggest a complex circumstellar medium surrounding the progenitor star at the time of explosion, with a first dense shell produced during the very late stages of its evolution being swept up by the rapidly expanding ejecta within the first $sim6,rm{d}$ of the supernova evolution, while signatures of interaction are observed also at later phases. Hydrodynamical models support the scenario in which linearly declining Type II supernovae are predicted to arise from massive yellow super/hyper giants depleted of most of their hydrogen layers.
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We present optical and ultraviolet photometry, as well as optical spectra, for the type II supernova (SN) 2015bf. Our observations cover the phases from $sim 2$ to $sim 200$ d after explosion. The first spectrum is characterised by a blue continuum with a blackbody temperature of $sim 24,000$K and flash-ionised emission lines. After about one week, the spectra of SN 2015bf evolve like those of a regular SN II. From the luminosity of the narrow emission component of H$alpha$, we deduce that the mass-loss rate is larger than $sim 3.7times10^{-3},{rm M_odot,yr^{-1}}$. The disappearance of the flash features in the first week after explosion indicates that the circumstellar material is confined within $sim 6 times 10^{14}$ cm. Thus, we suggest that the progenitor of SN 2015bf experienced violent mass loss shortly before the supernova explosion. The multiband light curves show that SN 2015bf has a high peak luminosity with an absolute visual magnitude $M_V = -18.11 pm 0.08$ mag and a fast post-peak decline with a $V$-band decay of $1.22 pm 0.09$ mag within $sim 50$ d after maximum light. Moreover, the $R$-band tail luminosity of SN 2015bf is fainter than that of SNe~II with similar peak by 1--2 mag, suggesting a small amount of ${rm ^{56}Ni}$ ($sim 0.009,{rm M_odot}$) synthesised during the explosion. Such a low nickel mass indicates that the progenitor of SN 2015bf could be a super-asymptotic-giant-branch star that collapsed owing to electron capture.
We present an analysis of a new sample of type II core-collapse supernovae (SNe II) occurring within low-luminosity galaxies, comparing these with a sample of events in brighter hosts. Our analysis is performed comparing SN II spectral and photometric parameters and estimating the influence of metallicity (inferred from host luminosity differences) on SN II transient properties. We measure the SN absolute magnitude at maximum, the light-curve plateau duration, the optically thick duration, and the plateau decline rate in the V-band, together with expansion velocities and pseudo-equivalent-widths (pEWs) of several absorption lines in the SN spectra. For the SN host galaxies, we estimate the absolute magnitude and the stellar mass, a proxy for the metallicity of the host galaxy. SNe II exploding in low luminosity galaxies display weaker pEWs of Fe II $lambda5018$, confirming the theoretical prediction that metal lines in SN II spectra should correlate with metallicity. We also find that SNe II in low-luminosity hosts have generally slower declining light curves and display weaker absorption lines. We find no relationship between the plateau duration or the expansion velocities with SN environment, suggesting that the hydrogen envelope mass and the explosion energy are not correlated with the metallicity of the host galaxy. This result supports recent predictions that mass-loss for red supergiants is independent of metallicity.
We present the photometry and spectroscopy of SN 2015an, a Type II Supernova (SN) in IC 2367. The recombination phase of the SN lasts up to $sim$120 d, with a decline rate of 1.24 mag/100d, higher than the typical SNe IIP. The SN exhibits bluer colours than most SNe II, indicating higher ejecta temperatures. The absolute $V$-band magnitude of SN 2015an at 50 d is $-$16.83$pm$0.04 mag, pretty typical for SNe II. However, the $^{56}$Ni mass yield, estimated from the tail $V$-band light curve to be 0.021$pm$0.010 M$_odot$, is comparatively low. The spectral properties of SN 2015an are atypical, with low H$alpha$ expansion velocity and presence of high velocity component of H$alpha$ at early phases. Moreover, the continuum exhibits excess blue flux up to $sim$50 d, which is interpreted as a progenitor metallicity effect. The high velocity feature indicates ejecta-circumstellar material interaction at early phases. The semi-analytical modelling of the bolometric light curve yields a total ejected mass of $sim$12 M$_odot$, a pre-supernova radius of $sim$388~R$_odot$ and explosion energy of $sim$1.8 foe.
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