The nebular spectra of SN 2012aw and constraints on stellar nucleosynthesis from oxygen emission lines

We present nebular phase optical and near-infrared spectroscopy of the Type IIP supernova SN 2012aw combined with NLTE radiative transfer calculations applied to ejecta from stellar evolution/explosion models. Our spectral synthesis models generally show good agreement with the ejecta from a MZAMS = 15 Msun progenitor star. The emission lines of oxygen, sodium, and magnesium are all consistent with the nucleosynthesis in a progenitor in the 14 - 18 Msun range. We also demonstrate how the evolution of the oxygen cooling lines of [O I] 5577 A, [O I] 6300 A, and [O I] 6364 A can be used to constrain the mass of oxygen in the non-molecularly cooled ashes to < 1 Msun, independent of the mixing in the ejecta. This constraint implies that any progenitor model of initial mass greater than 20 Msun would be difficult to reconcile with the observed line strengths. A stellar progenitor of around MZAMS = 15 Msun can consistently explain the directly measured luminosity of the progenitor star, the observed nebular spectra, and the inferred pre-supernova mass-loss rate. We conclude that there is still no convincing example of a Type IIP explosion showing the nucleosynthesis expected from a MZAMS > 20 Msun progenitor.Comment: Accepted for publication in MNRA

Identification of adaptation in human postural control using GARCH models

Human postural dynamics was investigated in twelve normal subjects by means of a force platform recording body sway induced by bipolar transmastoid galvanic stimulation of the vestibular nerve and labyrinth. We modeled the stabilizing forces actuated by the feet as resulting from complex muscular activity subject to feedback of body velocity and position. Time series analysis demonstrated that a transfer function from stimulus to sway-force response with specific parameters could be identified. In addition, adaptation to the vestibular stimulus was demonstrated to exist. Residual GARCH modeling (generalized autoregressive conditional heteroskedasticity) suggested a postural adaptation time constant in the range of 40-50 s. The results suggest means to evaluate adaptive behavior in postural control and in other physiological context

iPTF16abc and the population of Type Ia supernovae: Comparing the photospheric, transitional and nebular phases

Key information about the progenitor system and the explosion mechanism of Type Ia supernovae (SNe~Ia) can be obtained from early observations, within a few days from explosion. iPTF16abc was discovered as a young SN~Ia with excellent early time data. Here, we present photometry and spectroscopy of the SN in the nebular phase. A comparison of the early time data with a sample of SNe~Ia shows distinct features, differing from normal SNe~Ia at early phases but similar to normal SNe~Ia at a few weeks after maximum light (i.e. the transitional phase) and well into the nebular phase. The transparency timescales ($t_0$) for this sample of SNe~Ia range between $\sim$ 25 and 41 days indicating a diversity in the ejecta masses. $t_0$ also weakly correlates with the peak bolometric luminosity, consistent with the interpretation that SNe with higher ejecta masses would produce more $^{56}$Ni. Comparing the $t_0$ and the maximum luminosity, L$_{max}$\, distribution of a sample of SNe~Ia to predictions from a wide range of explosion models we find an indication that the sub-Chandrasekhar mass models span the range of observed values. However, the bright end of the distribution can be better explained by Chandrasekhar mass delayed detonation models, hinting at multiple progenitor channels to explain the observed bolometric properties of SNe~Ia. iPTF16abc appears to be consistent with the predictions from the M$_{ch}$ models.Comment: 13 pages, 8 figures, accepted for publication in MNRA

Chandra X-Ray Point Sources, including Supernova 1979C, in the Spiral Galaxy M100

Six x-ray point sources, with luminosities of $4 \times 10^{38} - 2 \times 10^{39} \rm ergs s^{-1}$ in the 0.4--7 keV band, were detected in Chandra observations of the spiral galaxy M100. One source is identified with supernova SN 1979C and appears to have roughly constant x-ray flux for the period 16--20 years after the outburst. The x-ray spectrum is soft, as would be expected if the x-ray emission is due to the interaction of supernova ejecta with circumstellar matter. Most of the other sources are variable either within the Chandra observation or when compared to archival data. None are coincident with the peak of the radio emission at the nucleus. These sources have harder spectra than the supernova and are likely x-ray binaries. M100 has more bright x-ray sources than typical for spiral galaxies of its size. This is likely related to active star formation occurring in the galaxy.Comment: accepted by the Astrophysical Journal, 7 page

Chandra and ASCA X-ray Observations of the Radio Supernova SN1979C IN NGC 4321

We report on the X-ray observation of the radio selected supernova SN1979C carried out with ASCA in 1997 December and serendipitously available from a Chandra Guaranteed Time Observation in 1999 November. The supernova, of type SN II-Linear (SN IIL), was first observed in the optical and occurred in the weakly barred, almost face on spiral galaxy NGC 4321 (M100). The galaxy, a member of the Virgo S cluster, is at a distance of 17.1 Mpc, and contains at least three other supernovae discovered in this century. The useful exposure time was ~25 ks for the Solid-State Imaging Spectrometer (SIS), ~28 ks for the Gas Scintillation Imaging Spectrometer (GIS), and ~2.5 ks for Chandra's Advanced CCD Imaging Spectrometer (ACIS). No point source was detected at the radio position of SN1979C in a 3' diameter half power response circle in the ASCA data. The background and galaxy subtracted SN signal had a 3sigma upper limit to the flux of 6.3x10^-14 ergs/s/cm^-2 in the full ASCA SIS band (0.4-10.0 keV) and a 3sigma upper limit of <3-4x10^-14 erg/s/cm^2 in the 2-10 keV band. In the Chandra data, a source at the position of SN1979C is marginally detected at energies below 2 keV at a flux consistent with the ROSAT HRI detection in 1995. At energies above 2 keV, no source is detected with an upper limit of ~3x10^-14 erg/s/cm^-2. These measurements give the first ever x-ray flux limit of a Type IIL SN above 2 keV which is an important diagnostic of the outgoing shock wave ploughing through the circumstellar medium.Comment: 8 pages, 2 figures, accepted A

Goodness-of-Fit Tests DIFF1 and DIFF2 for Locally-Normalized Supernova Spectra

Two quantitative tests DIFF1 and DIFF2 for measuring goodness-of-fit between two locally-normalized supernova spectra are presented. Locally-normalized spectra are obtained by dividing a spectrum by the same spectrum smoothed over a wavelength interval relatively large compared to line features, but relatively small compared to continuum features. DIFF1 essentially measures the mean relative difference between the line patterns of locally-normalized spectra and DIFF2 is DIFF1 minimized by a relative logarithmic wavelength shift between the spectra: the shift is effectively an artificial relative Doppler shift. Both DIFF1 and DIFF2 measure the physical similarity of line formation, and thus of supernovae. DIFF1 puts more weight on overall physical similarity of the supernovae than DIFF2 because the DIFF2 shift compensates somewhat for some physical distinction in the supernovae. Both tests are useful in ordering supernovae into empirical groupings for further analysis. We present some examples of locally-normalized spectra for Type IIb supernova SN 1993J with some analysis of these spectra. The UV parts of two of the SN 1993J spectra are HST spectra that have not been published before. We also give an example of fitted locally-normalized spectra and, as an example of the utility of DIFF1 and DIFF2, some preliminary statistical results for hydrogen-deficient core-collapse (HDCC) supernova spectra. This paper makes use of and refers to material to found at the first author's online supernova spectrum database SUSPEND (SUpernovae Spectra PENDing further analysis: see http://www.nhn.ou.edu/~jeffery/astro/sne/spectra/spectra.html)Comment: 6 coauthors, 53 pages, 6 Figures, accepted by the Astrophysical Journal Supplement Series Version 2: Improved discussion from Version

Metallicity at the explosion sites of interacting transients

Context. Some circumstellar-interacting (CSI) supernovae (SNe) are produced by the explosions of massive stars that have lost mass shortly before the SN explosion. There is evidence that the precursors of some SNe IIn were luminous blue variable (LBV) stars. For a small number of CSI SNe, outbursts have been observed before the SN explosion. Eruptive events of massive stars are named as SN impostors (SN IMs) and whether they herald a forthcoming SN or not is still unclear. The large variety of observational properties of CSI SNe suggests the existence of other progenitors, such as red supergiant (RSG) stars with superwinds. Furthermore, the role of metallicity in the mass loss of CSI SN progenitors is still largely unexplored. Aims. Our goal is to gain insight on the nature of the progenitor stars of CSI SNe by studying their environments, in particular the metallicity at their locations. Methods. We obtain metallicity measurements at the location of 60 transients (including SNe IIn, SNe Ibn, and SN IMs), via emission-line diagnostic on optical spectra obtained at the Nordic Optical Telescope and through public archives. Metallicity values from the literature complement our sample. We compare the metallicity distributions among the different CSI SN subtypes and to those of other core-collapse SN types. We also search for possible correlations between metallicity and CSI SN observational properties. Results. We find that SN IMs tend to occur in environments with lower metallicity than those of SNe IIn. Among SNe IIn, SN IIn-L(1998S-like) SNe show higher metallicities, similar to those of SNe IIL/P, whereas long-lasting SNe IIn (1988Z-like) show lower metallicities, similar to those of SN IMs. The metallicity distribution of SNe IIn can be reproduced by combining the metallicity distributions of SN IMs (that may be produced by major outbursts of massive stars like LBVs) and SNe IIP (produced by RSGs). The same applies to the distributions of the Normalized Cumulative Rank (NCR) values, which quantifies the SN association to H II regions. For SNe IIn, we find larger mass-loss rates and higher CSM velocities at higher metallicities. The luminosity increment in the optical bands during SN IM outbursts tend to be larger at higher metallicity, whereas the SN IM quiescent optical luminosities tend to be lower. Conclusions. The difference in metallicity between SNe IIn and SN IMs suggests that LBVs are only one of the progenitor channels for SNe IIn, with 1988Z-like and 1998S-like SNe possibly arising from LBVs and RSGs, respectively. Finally, even though linedriven winds likely do not primarily drive the late mass-loss of CSI SN progenitors, metallicity has some impact on the observational properties of these transients. Key words. supernovae: general - stars: evolution - galaxies: abundancesComment: Submitted to Astronomy and Astrophysics on 28/02/2015; submitted to arXiv after the 1st referee repor