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Register a new userNear-Infrared Spectroscopy of SN 2017eaw in 2017: Carbon Monoxide and Dust Formation in a Type II-P Supernova
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The origin of dust in the early Universe has been the subject of considerable debate. Core-collapse supernovae (ccSNe), which occur several million years after their massive progenitors form, could be a major source of that dust, as in the local universe several ccSNe have been observed to be copious dust producers. Here we report nine near-infrared (0.8 - 2.5 micron) spectra of the Type II-P SN 2017eaw in NGC 6946, spanning the time interval 22 - 205 days after discovery. The specta show the onset of CO formation and continuum emission at wavelengths greater than 2.1 micron from newly-formed hot dust, in addition to numerous lines of hydrogen and metals, which reveal the change in ionization as the density of much of the ejecta decreases. The observed CO masses estimated from an LTE model are typically 10^{-4} Msun during days 124 - 205, but could be an order of magnitude larger if non-LTE conditions are present in the emitting region. The timing of the appearance of CO is remarkably consistent with chemically controlled dust models of Sarangi & Cherchneff.
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We present infrared (IR) photometry and spectroscopy of the Type II-P SN 2017eaw and its progenitor in the nearby galaxy NGC 6946. Progenitor observations in the Ks band in 4 epochs from 1 year to 1 day before the explosion reveal no significant variability in the progenitor star greater than 6% that last longer than 200 days. SN 2017eaw is a typical SN II-P with near-IR and mid-IR photometric evolution similar to those of SNe 2002hh and 2004et, other normal SNe II-P in the same galaxy. Spectroscopic monitoring between 389 and 480 days post explosion reveals strong CO first overtone emission at 389 d, with a line profile matching that of SN 1987A from the same epoch, indicating $sim 10^{-3} , M_{odot}$ of CO at 1,800 K. From the 389 d epoch until the most recent observation at 566 d, the first overtone feature fades while the 4.5 $mu$m excess, likely from the CO fundamental band, remains. This behavior indicates that the CO has not been destroyed, but that the gas has cooled enough that the levels responsible for first overtone emissions are no longer populated. Finally, the evolution of Spitzer 3.6 $mu$m photometry shows evidence for dust formation in SN 2017eaw, with a dust mass of $10^{-6}$ or $10^{-4},M_{odot}$ assuming carbonaceous or silicate grains respectively.
We present near-infrared spectroscopy of the NGC 5128 supernova SN 2016adj in the first 2 months following discovery. We report the detection of first overtone carbon monoxide emission at $sim58.2$ d after discovery, one of the earliest detections of CO in an erupting supernova. We model the CO emission to derive the CO mass, temperature and velocity, assuming both pure $^{12}$CO and a composition that includes $^{13}$CO; the case for the latter is the isotopic analyses of meteoritic grains, which suggest that core collapse supernovae can synthesise significant amounts of $^{13}$C. Our models show that, while the CO data are adequately explained by pure $^{12}$CO, they do not preclude the presence of $^{13}$CO, to a limit of $^{12}$C/$^{13}$C $> 3$, the first constraint on the $^{12}$C/$^{13}$C ratio determined from near-infrared observations. We estimate the reddening to the object, and the effective temperature from the energy distribution at outburst. We discuss whether the ejecta of SN 2016adj may be carbon-rich, what the infrared data tell us about the classification of this supernova, and what implications the early formation of CO in supernovae may have for CO formation in supernovae in general.
We present near-infrared and optical observations of the Type Ic Supernova (SN) 2020oi in the galaxy M100 and the broad-lined Type Ic SN2020bvc in UGC 9379, using Gemini, LCO, SOAR, and other ground-based telescopes. The near-IR spectrum of SN2020oi at day 63 since the explosion shows strong CO emissions and a rising K-band continuum, which is the first unambiguous dust detection from a Type Ic SN. Non-LTE CO modeling shows that CO is still optically thick, and that the lower limit to the CO mass is 0.001 Msun. The dust temperature is 810 K, and the dust mass is ~10^(-5) Msun. We explore the possibilities that the dust is freshly formed in the ejecta, heated dust in the pre-existing circumstellar medium, and an infrared echo. The light curves of SN2020oi are consistent with a STELLA model with canonical explosion energy, 0.07 Msun Ni mass, and 0.7 Msun ejecta mass. A model of high explosion energy of ~10^(52) erg, 0.4 Msun Ni mass, 6.5 Msun ejecta mass with the circumstellar matter, reproduces the double-peaked light curves of SN2020bvc. We observe temporal changes of absorption features of the IR Ca~II triplet, S~I at 1.043 micron, and Fe~II at 5169 Angstrom. The blue-shifted lines indicate high velocities, up to 60,000 km/s for SN2020bvc and 20,000 km/s for SN2020oi, and the expansion velocity rapidly declines before the optical maximum. We present spectral signatures and diagnostics of CO and SiO molecular bands between 1.4 and 10 microns.
We present near-infrared (NIR) observations of Nova V5668 Sgr, discovered in outburst on 2015 March 15.634 UT, between 2d to 107d after outburst. NIR spectral features are used to classify it as a FeII class of nova. The spectra follow the evolution of the spectral lines from a P Cygni stage to a pure emission phase where the shape of the profiles suggests the presence of a bipolar flow. A notable feature is the presence of carbon monoxide first overtone bands which are seen in emission. The CO emission is modeled to make estimates of the mass, temperature and column density to be (0.5--2.0)$times$ 10$^{-8}$ M$_odot$, 4000 $pm$ 300K and (0.36--1.94)$times$ 10$^{19}$ cm$^{-2}$ respectively. The $^{12}$C/$^{13}$C ratio is estimated to be $sim$ 1.5. V5668 Sgr was a strong dust producer exhibiting the classical deep dip in its optical light curve during dust formation. Analysis of the dust SED yields a dust mass of 2.7 $times$ 10${^{rm -7}}$ $M_odot $, a blackbody angular diameter of the dust shell of 42 mas and a distance estimate to the nova of 1.54 kpc which agrees with estimates made from MMRD relations.
We present near-infrared (NIR) time-series spectroscopy, as well as complementary ultraviolet (UV), optical, and NIR data, of the Type Ia supernova (SN Ia) iPTF13ebh, which was discovered within two days from the estimated time of explosion. The first NIR spectrum was taken merely 2.3 days after explosion and may be the earliest NIR spectrum yet obtained of a SN Ia. The most striking features in the spectrum are several NIR C I lines, and the C I {lambda}1.0693 {mu}m line is the strongest ever observed in a SN Ia. Interestingly, no strong optical C II counterparts were found, even though the optical spectroscopic time series began early and is densely-cadenced. Except at the very early epochs, within a few days from the time of explosion, we show that the strong NIR C I compared to the weaker optical C II appears to be general in SNe Ia. iPTF13ebh is a fast decliner with {Delta}m15(B) = 1.79 $pm$ 0.01, and its absolute magnitude obeys the linear part of the width-luminosity relation. It is therefore categorized as a transitional event, on the fast-declining end of normal SNe Ia as opposed to subluminous/91bg-like objects. iPTF13ebh shows NIR spectroscopic properties that are distinct from both the normal and subluminous/91bg-like classes, bridging the observed characteristics of the two classes. These NIR observations suggest composition and density of the inner core similar to that of 91bg-like events, and a deep reaching carbon burning layer not observed in slower declining SNe Ia. There is also a substantial difference between the explosion times inferred from the early-time light curve and the velocity evolution of the Si II {lambda}0.6355 {mu}m line, implying a long dark phase of ~ 4 days.
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