Optical and infrared spectroscopy of the type IIn SN 1998S: days 3–127

By A. Fassia, W. Meikle, Nikolai Chugai, T. Geballe, Peter Lundqvist, N. Walton, D. Pollacco, Sylvain Veilleux, G. Wright, M. Pettini and 7 more. 2000

166 citations recorded by the source corpus.

We present contemporary optical and infrared spectroscopic observations of the type IIn SN 1998S covering the period between 3 and 127 days after discovery. During the first week the spectra are characterized by prominent broad H, He and C iii/N iii emission lines with narrow peaks, superimposed on a very blue continuum (T∼24 000 K). In the following two weeks the C iii/N iii emission vanished, together with the broad emission components of the H and He lines. Broad, blueshifted absorption components appeared in the spectra. The temperature of the continuum also dropped to ∼14 000 K. By the end of the first month the spectrum comprised broad, blueshifted absorptions in H, He, Si ii, Fe ii and Sc ii. By day 44, broad emission components in H and He reappeared in the spectra. These persisted to as late as days ∼100–130, becoming increasingly asymmetric. We agree with Leonard et al. that the broad emission lines indicate interaction between the ejecta and circumstellar material (CSM) emitted by the progenitor. We also agree that the progenitor of SN 1998S appears to have gone through at least two phases of mass-loss, giving rise to two CSM zones. Examination of the spectra indicates that the inner zone extended to ≤90 au, while the outer CSM extended from 185 au to over 1800 au. We also present high-resolution spectra obtained at days 17 and 36. These spectra exhibit narrow P Cygni H i and He i lines superimposed on shallower, broader absorption components. Narrow lines of [N ii], [O iii], [Ne iii] and [Fe iii] are also seen. We attribute the narrow lines to recombination and heating following ionization of the outer CSM shell by the UV/X-ray flash at shock breakout. Using these lines, we show that the outer CSM had a velocity of 40–50 km s−1. Assuming a constant velocity, we can infer that the outer CSM wind commenced more than 170 years ago, and ceased about 20 years ago, while the inner CSM wind may have commenced less than 9 years ago. During the era of the outer CSM wind the outflow from the progenitor was high – at least ∼2×10−5 M⊙ yr−1. This corresponds to a mass-loss of at least ∼0.003 M⊙, suggesting a massive progenitor. The shallower, broader absorption is of width ∼350 km s−1, and may have arisen from a component of the outer CSM shell produced when the progenitor was going through a later blue supergiant phase. Alternatively, it may have been produced by the acceleration of the outer CSM by the radiation pressure of the UV precursor. We also describe and model first-overtone emission in carbon monoxide observed in SN 1998S. We deduce a CO mass of ∼10−3 M⊙ moving at ∼2200 km s−1, and infer a mixed metal/He core of about 4 M⊙, again indicating a massive progenitor. Only three core-collapse supernovae have been observed in the K band at post-100 days, and all three have exhibited emission from CO.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/9e5e895484633e29b9f2b255da0580789b7a024b

How researchers see this paper

The researchers whose trusted networks rank it highest, strongest advocate first. Every researcher gets a different order.

In Astronomy and Astrophysics

1. N. Smith
2. S. Smartt
3. A. Filippenko
4. E. Berger
5. Ryan Chornock
6. Weidong Li
7. J. Silverman
8. B. Metzger

Citations in the corpus

• The fast, luminous ultraviolet transient AT2018cow: extreme supernova, or disruption of a star by an intermediate-mass black hole? (2018, background): “…(which can also remain hot for several weeks after explosion, and are emission-dominated by definition): in the bottom panel of Figure 11 we plot AT2018cow versus an early spectrum of SN1998S from Fassia et al. (2001), which shows a similar blue continuum and most of the same H and He transitions.”
• HIGH-DENSITY CIRCUMSTELLAR INTERACTION IN THE LUMINOUS TYPE IIn SN 2010jl: THE FIRST 1100 DAYS (2013, background): “…as a less extreme case of a Type IIn SN. Initially it showed typical Type IIn signatures with narrow symmetric lines (Leonard et al. 2000; Fassia et al. 2001) dominated by electron scattering of H and He I lines (Chugai 2001) The symmetric lines disappeared after about a week and instead…”
• The Distance to SN 1999em from the Expanding Photosphere Method (2001, background): “The spectroscopic studies have also been mostly limited to optical wavelengths (3000È10000 and exceptA ), for the Type II SN 1987A (Elias et al 1988 ; Meikle et al. 1989), SN 1995V (Fassia et al. 1998), and SN 19985 (Fassia et al. 2001), few spectra have been obtained beyond this range.”
• The Zwicky Transient Facility: Science Objectives (2019, background): “…may persist for days (“flash spectroscopy”, Gal-Yam et al. 2014b; Khazov et al. 2016b; Yaron et al. 2017b, weeks (e.g., SN 1998S, Li et al. 1998; Fassia et al. 2000, 2001; SN 2005gl, Gal-Yam et al. 2007; SN 2010mc Ofek et al. 2013b; PTF 12glz Soumagnac et al. 2018), or years (e.g., SN 1988Z,…”
• SN 2006tf: Precursor Eruptions and the Optically Thick Regime of Extremely Luminous Type IIn Supernovae (2008, methodology): “We encourage near-infrared spectroscopy of SN 2006tf in order to determine if it shows the expected 2.3 µm CO bandhead emission, as was seen in SN 1998S (Gerardy et al. 2000; Fassia et al. 2001).”
• SN 2006gy: Discovery of the Most Luminous Supernova Ever Recorded, Powered by the Death of an Extremely Massive Star like η Carinae (2006, unknown): “Similar absorption speeds were seen in the narrow P Cygni absorption of SN 1998S, which Fassia et al. (2001) also interpreted as a prior blue-supergiant phase.”
• SN 2005ap: A Most Brilliant Explosion (2007, background): “There have been SNe with continua slopes about as blue as SN 2005ap (e.g. SN 1998S; Fassia et al. 2001), but the existence of CIII , N III , and OIII features is unprecedented.”
• SPECTRAL EVOLUTION OF THE EXTRAORDINARY TYPE IIn SUPERNOVA 2006gy (2009, background): “Their spectra at 90–100 days after explosion do not resemble spectra of SN 2006gy at a comparable epoch because they have already become optically thin by that point (see Leonard et al. 2000; Fassia et al. 2001; Pastorello et al. 2002).”
• Optical and near infrared coverage of SN 2004et: physical parameters and comparison with other type IIP supernovae (2009, methodology): “The feature identification of both the IJ andHK bands was carried out following Fassia et al. (2001) and Gerardy et al. (2000).”
• Broad emission lines from the opaque electron‐scattering environment of SN 1998S (2001, methodology): “…103 km s−1, which is hinted by the UV lines in HST spectra on March 16 (Lentz et al. 2001), we obtain that the narrow component (or unscattered emission) of Hα in the spectrum on March 6 (Fassia et al. 2001) comprises roughly 20 − 25% of the overall line emission, which suggests U(τT) ≈ 0.2−0.25.”
• The death of massive stars – I. Observational constraints on the progenitors of Type II-P supernovae (2008, unknown): “Supernova Galaxy Vvir Type HST FOV Comments Core-collapse 1998A IC 2627 1974 IIpec – Pastorello et al. (2005)SN1987A-like 1998S NGC 3877 1115 IIn – Fassia et al. (2001) 1998bm IC 2458 1810 II – Li et al. (1998), unknown subtype 1998bv PGC2302994 1794 IIP – Kniazeb (1998) 1998dl NGC 1084 1298 IIP –…”
• CALTECH CORE-COLLAPSE PROJECT (CCCP) OBSERVATIONS OF TYPE IIn SUPERNOVAE: TYPICAL PROPERTIES AND IMPLICATIONS FOR THEIR PROGENITOR STARS (2010, background): “Leonard et al. (2000) present an extensive spectroscopic and spectropolarimetric analysis, while Fassia et al. (2000, 2001) study large optical/IR photometric and spectroscopic data sets.”
• Carnegie Supernova Project: Observations of Type IIn supernovae ⋆ (2013, methodology): “If we assume that SN 2008fq had an inner CSM (ICSM) like that of SN 1998S (Leonard et al. 2000; Fassia et al. 2001), with the first spectrum observed approximately 10 days after explosion and the above mentioned vmaxejecta, the ICSM could not be more extended thanR in CSM ≈ 7.8×1014 cm.”
• The Type IIn supernova 1994W: evidence for the explosive ejection of a circumstellar envelope (2004, background): “…with narrow lines are SNe 1997cy (Germany et al. 1994; Turatto et al. 2000), 1998S (Filippenko & Moran 1998; Bowen et al. 2000; Leonard et al. 2000; Fassia et al. 2001; Chugai et al. 2002; Fransson et al. 2004), 1999E (Filippenko 2000; Rigon et al. 2003) and, most remarkably, SN 2002ic, which has…”
• High luminosity, slow ejecta and persistent carbon lines: SN 2009dc challenges thermonuclear explosion scenarios (2010, background): “In fact, if the (highly un- certain) detection of CO emission in the +84.3 d NIR spectrum was correct, the additional cooling through molecular bands might create favourable conditions for dust formation at a later moment (Fassia et al. 2001).”