We present an investigation of the optical spectra of 264 low-redshift (z < 0.2) Type Ia supernovae (SNe Ia) discovered by the Palomar Transient Factory, an untargeted transient survey. We focus on ...velocity and pseudo-equivalent width measurements of the Si ii 4130, 5972, and 6355 Å lines, as well those of the Ca ii near-infrared (NIR) triplet, up to +5 days relative to the SN B-band maximum light. We find that a high-velocity component of the Ca ii NIR triplet is needed to explain the spectrum in ∼95 per cent of SNe Ia observed before −5 days, decreasing to ∼80 per cent at maximum. The average velocity of the Ca ii high-velocity component is ∼8500 km s−1 higher than the photospheric component. We confirm previous results that SNe Ia around maximum light with a larger contribution from the high-velocity component relative to the photospheric component in their Ca ii NIR feature have, on average, broader light curves and lower Ca ii NIR photospheric velocities. We find that these relations are driven by both a stronger high-velocity component and a weaker contribution from the photospheric Ca ii NIR component in broader light curve SNe Ia. We identify the presence of C ii in very-early-time SN Ia spectra (before −10 days), finding that >40 per cent of SNe Ia observed at these phases show signs of unburnt material in their spectra, and that C ii features are more likely to be found in SNe Ia having narrower light curves.
A series of optical and one near-infrared nebular spectra covering the first year of the Type Ia supernova SN 2011fe are presented and modelled. The density profile that proved best for the early ...optical/ultraviolet spectra, '...-11fe', was extended to lower velocities to include the regions that emit at nebular epochs. Model ...-11fe is intermediate between the fast deflagration model W7 and a low-energy delayed-detonation. Good fits to the nebular spectra are obtained if the innermost ejecta are dominated by neutron-rich, stable Fe-group species, which contribute to cooling but not to heating. The correct thermal balance can thus be reached for the strongest FeII and FeIII lines to be reproduced with the observed ratio. The ... mass thus obtained is ~0.47 plus or minus 0.05 M... The bulk of 56Ni has an outermost velocity of ~8500 km s... The mass of stable iron is ~0.23 plus or minus 0.03 M... Stable Ni has low abundance, ... This is sufficient to reproduce an observed emission line near 7400 A. A sub-Chandrasekhar explosion model with mass ... and no central stable Fe does not reproduce the observed line ratios. A mock model where neutron-rich Fe-group species are located above 56Ni following recent suggestions is also shown to yield spectra that are less compatible with the observations. The densities and abundances in the inner layers obtained from the nebular analysis, combined with those of the outer layers previously obtained, are used to compute a synthetic bolometric light curve, which compares favourably with the light curve of SN 2011fe. (ProQuest: ... denotes formulae/symbols omitted.)
SN 2013dy is a Type Ia supernova (SN Ia) for which we have compiled an extraordinary data set spanning from 0.1 to ∼ 500 d after explosion. We present 10 epochs of ultraviolet (UV) through ...near-infrared (NIR) spectra with Hubble Space Telescope/Space Telescope Imaging Spectrograph, 47 epochs of optical spectra (15 of them having high resolution), and more than 500 photometric observations in the BVrRiIZYJH bands. SN 2013dy has a broad and slowly declining light curve (Δm
15(B) = 0.92 mag), shallow
$\mathrm{Si}\,\small {II}\,\lambda 6355$
absorption, and a low velocity gradient. We detect strong C ii in our earliest spectra, probing unburned progenitor material in the outermost layers of the SN ejecta, but this feature fades within a few days. The UV continuum of SN 2013dy, which is strongly affected by the metal abundance of the progenitor star, suggests that SN 2013dy had a relatively high-metallicity progenitor. Examining one of the largest single set of high-resolution spectra for an SN Ia, we find no evidence of variable absorption from circumstellar material. Combining our UV spectra, NIR photometry, and high-cadence optical photometry, we construct a bolometric light curve, showing that SN 2013dy had a maximum luminosity of
$10.0^{+4.8}_{-3.8} \times 10^{42}$
erg s−1. We compare the synthetic light curves and spectra of several models to SN 2013dy, finding that SN 2013dy is in good agreement with a solar-metallicity W7 model.
We present an optical nebular spectrum of the nearby Type Ia supernova 2011fe, obtained 981 d after explosion. SN 2011fe exhibits little evolution since the +593 d optical spectrum, but there are ...several curious aspects in this new extremely late-time regime. We suggest that the persistence of the ∼5800 Å feature is due to Na I D, and that a new emission feature at ∼7300 Å may be Ca II. Also, we discuss whether the new emission feature at ∼6400 Å might be Fe I or the high-velocity hydrogen predicted by Mazzali et al. The nebular feature at 5200 Å exhibits a linear velocity evolution of ∼350 km s− 1 per 100 d from at least +220 to +980 d, but the line's shape also changes in this time, suggesting that line blending contributes to the evolution. At ∼1000 d after explosion, flux from the SN has declined to a point where contribution from a luminous secondary could be detected. In this work, we make the first observational tests for a post-impact remnant star and constrain its temperature and luminosity to T ≳ 104 K and L ≲ 104 L⊙. Additionally, we do not see any evidence for narrow H α emission in our spectrum. We conclude that observations continue to strongly exclude many single-degenerate scenarios for SN 2011fe.
In this work, BVRI light curves of 55 Type II supernovae (SNe II) from the Lick Observatory Supernova Search programme obtained with the Katzman Automatic Imaging Telescope and the 1 m Nickel ...telescope from 2006 to 2018 are presented. Additionally, more than 150 spectra gathered with the 3 m Shane telescope are published. We conduct an analyse of the peak absolute magnitudes, decline rates, and time durations of different phases of the light and colour curves. Typically, our light curves are sampled with a median cadence of 5.5 d for a total of 5093 photometric points. In average, V-band plateau declines with a rate of 1.29 mag (100 d)(exp −1), which is consistent with previously published samples. For each band, the plateau slope correlates with the plateau length and the absolute peak magnitude: SNe II with steeper decline have shorter plateau duration and are brighter. A time-evolution analysis of spectral lines in term of velocities and pseudo-equivalent widths is also presented in this paper. Our spectroscopic sample ranges between 1 and 200 d post-explosion and has a median ejecta expansion velocity at 50 d post-explosion of 6500 km s(exp −1) (H α line) and a standard dispersion of 2000 km s(exp −1). Nebular spectra are in good agreement with theoretical models using a progenitor star having a mass <16M⨀. All the data are available to the community and will help to understand SN II diversity better, and therefore to improve their utility as cosmological distance indicators.
We present the results of a survey using the WASP archive to search for high-frequency pulsations in F-, A- and B-type stars. Over 1.5 million targets have been searched for pulsations with ...amplitudes greater than 0.5 millimagnitude. We identify over 350 stars which pulsate with periods less than 30 min. Spectroscopic follow-up of selected targets has enabled us to confirm 10 new rapidly oscillating Ap stars, 13 pulsating Am stars and the fastest known δ Scuti star. We also observe stars which show pulsations in both the high-frequency domain and the low-frequency δ Scuti range. This work shows the power of the WASP photometric survey to find variable stars with amplitudes well below the nominal photometric precision per observation.
The Seyfert 1 galaxy Arp 151 was monitored as part of three reverberation mapping campaigns spanning 2008-2015. We present modeling of these velocity-resolved reverberation mapping data sets using a ...geometric and dynamical model for the broad-line region (BLR). By modeling each of the three data sets independently, we infer the evolution of the BLR structure in Arp 151 over a total of 7 yr and constrain the systematic uncertainties in nonvarying parameters such as the black hole mass. We find that the BLR geometry of a thick disk viewed close to face-on is stable over this time, although the size of the BLR grows by a factor of ∼2. The dynamics of the BLR are dominated by inflow, and the inferred black hole mass is consistent for the three data sets, despite the increase in BLR size. Combining the inference for the three data sets yields a black hole mass and statistical uncertainty of log10( / ) = with a standard deviation in individual measurements of 0.13 dex.
The nearby Type Ia supernovae (SNe Ia) 2011fe and 2011by had nearly identical photospheric phase optical spectra, light-curve widths, and photometric colours, but at peak brightness SN 2011by reached ...a fainter absolute magnitude in all optical bands and exhibited lower flux in the near-ultraviolet (NUV). Based on those data, Foley & Kirshner argue that the progenitors of SNe 2011by and 2011fe had supersolar and subsolar metallicity, respectively, and that SN 2011fe generated 1.7 times the amount of 56Ni as SN 2011by. With this work, we extend the comparison of these SNe Ia to 10 d before and 300 d after maximum brightness with new spectra and photometry. We show that the nebular phase spectra of SNe 2011fe and 2011by are almost identical, and do not support a factor of 1.7 difference in 56Ni mass. Instead, we find it plausible that the Tully-Fisher distance for SN 2011by is an underestimate, in which case these SNe Ia may have reached similar peak luminosity, formed similar amounts of 56Ni, and had lower metallicity progenitors than previously estimated. Regardless of the true distance to SN 2011by, we find that the relative progenitor metallicity difference remains well supported by their disparity in NUV flux, which we show to be even stronger at pre-maximum epochs -- although contributions from differences in total ejecta mass, viewing angle, or progenitor density cannot be ruled out. We also demonstrate that, independent of distance modulus, SN 2011by exhibits a late-time luminosity excess that cannot be explained by a light echo, but is more likely to be the result of greater energy trapping by the nucleosynthetic products of SN 2011by.
We analyse the fifth rapidly oscillating Ap (roAp) star reported in the Kepler field, KIC 7582608, discovered with the SuperWASP (Wide Angle Search for Planets) project. The object shows a ...high-frequency pulsation at 181.7324 d−1 (P = 7.9 min) with an amplitude of 1.45 mmag, and low-frequency rotational modulation corresponding to a period of 20.4339 d with an amplitude of 7.64 mmag. Spectral analysis confirms the Ap nature of the target, with characteristic lines of Eu ii, Nd iii and Pr iii present. The spectra are not greatly affected by broadening, which is consistent with the long rotational period found from photometry. From our spectral observations we derive a lower limit on the mean magnetic field modulus of 〈B〉 = 3.05 ± 0.23 kG. Long cadence Kepler observations show a frequency quintuplet split by the rotational period of the star, typical for an oblique pulsator. We suggest the star is a quadrupole pulsator with a geometry such that i ∼ 66° and β ∼ 33°. We detect frequency variations of the pulsation in both the WASP and Kepler data sets on many time-scales. Linear, non-adiabatic stability modelling allows us to constrain a region on the Hertzsprung–Russell diagram where the pulsations are unstable, an area consistent with observations.
ABSTRACT We present extensive optical (UBV RI, , and open CCD) and near-infrared (ZY JH) photometry for the very nearby Type IIP SN 2013ej extending from +1 to +461 days after shock breakout, ...estimated to be MJD 56496.9 0.3. Substantial time series ultraviolet and optical spectroscopy obtained from +8 to +135 days are also presented. Considering well-observed SNe IIP from the literature, we derive UBV RIJHK bolometric calibrations from UBV RI and unfiltered measurements that potentially reach 2% precision with a B − V color-dependent correction. We observe moderately strong Si ii as early as +8 days. The photospheric velocity ( ) is determined by modeling the spectra in the vicinity of Fe ii whenever observed, and interpolating at photometric epochs based on a semianalytic method. This gives km s−1 at +50 days. We also observe spectral homogeneity of ultraviolet spectra at +10-12 days for SNe IIP, while variations are evident a week after explosion. Using the expanding photosphere method, from combined analysis of SN 2013ej and SN 2002ap, we estimate the distance to the host galaxy to be Mpc, consistent with distance estimates from other methods. Photometric and spectroscopic analysis during the plateau phase, which we estimated to be 94 7 days long, yields an explosion energy of erg, a final pre-explosion progenitor mass of 15.2 4.2 and a radius of 250 70 . We observe a broken exponential profile beyond +120 days, with a break point at +183 16 days. Measurements beyond this break time yield a 56Ni mass of 0.013 0.001 M .
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