Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userThe Peculiar Balmer Decrement of SN 2009ip: Constraints on Circumstellar Geometry
92
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We present optical and near-IR spectroscopic observations of the luminous blue variable SN 2009ip during its remarkable photometric evolution of 2012. The spectra sample three key points in the SN 2009ip lightcurve, corresponding to its initial brightening in August (2012-A) and its dramatic rebrightening in early October (2012-B). Based on line fluxes and velocities measured in our spectra, we find a surprisingly low I(H-alpha)/I(H-beta) ~ 1.3-1.4 in the 2012-B spectra. Such a ratio implies either a rare Case B recombination scenario where H-alpha, but not H-beta, is optically thick, or an extremely high density for the circumstellar material of n_e > 10^13 cm^(-3) The H-alpha line intensity yields a minimum radiating surface area of >~20,000 AU^2 in H-alpha at the peak of SN 2009ips photometric evolution. Combined with the nature of this objects spectral evolution in 2012, a high circumstellar density and large radiating surface area imply the presence of a thin disk geometry around the central star (and, consequently, a possible binary companion), suggesting that the observed 2012-B rebrightening of SN 2009ip can be attributed to the illumination of the disks inner rim by fast-moving ejecta produced by the underlying events of 2012-A.
rate research
Read More
High resolution spectra are necessary to distinguish and correctly measure the Balmer emission lines due to the presence of strong metal and Balmer absorption features in the stellar continuum. This accurate measurement is necessary for use in emission line diagnostics, such as the Balmer decrement (i.e. Halpha/Hbeta), used to determine the attenuation of galaxies. Yet at high redshifts obtaining such spectra becomes costly. Balmer emission line equivalent widths are much easier to measure, requiring only low resolution spectra or even simple narrow band filters and therefore shorter observation times. However a correction for the stellar continuum is still needed for this equivalent width Balmer decrement. We present here a statistical analysis of the Sloan Digital Sky Survey Data Release 7 emission line galaxy sample, using the spectrally determined Balmer emission line fluxes and equivalent widths. Using the large numbers of galaxies available in the SDSS catalogue, we determined an equivalent width Balmer decrement including a statistically-based correction for the stellar continuum. Based on this formula, the attenuation of galaxies can now be obtained from low spectral resolution observations. In addition, this investigation also revealed an error in the Hbeta line fluxes, within the SDSS DR7 MPA/JHU catalogue, with the equivalent widths underestimated by average ~0.35A in the emission line galaxy sample. This error means that Balmer decrement determined attenuations are overestimated by a systematic 0.1 magnitudes in A_V, and future analyses of this sample need to include this correction.
We report the results of a 3 year-long dedicated monitoring campaign of a restless Luminous Blue Variable (LBV) in NGC 7259. The object, named SN 2009ip, was observed photometrically and spectroscopically in the optical and near-infrared domains. We monitored a number of erupting episodes in the past few years, and increased the density of our observations during eruptive episodes. In this paper we present the full historical data set from 2009-2012 with multi-wavelength dense coverage of the two high luminosity events between August - September 2012. We construct bolometric light curves and measure the total luminosities of these eruptive or explosive events. We label them the 2012a event (lasting ~50 days) with a peak of 3x10^41 erg/s, and the 2012b event (14 day rise time, still ongoing) with a peak of 8x10^42 erg/s. The latter event reached an absolute R-band magnitude of about -18, comparable to that of a core-collapse supernova (SN). Our historical monitoring has detected high-velocity spectral features (~13000 km/s) in September 2011, one year before the current SN-like event. This implies that the detection of such high velocity outflows cannot, conclusively, point to a core-collapse SN origin. We suggest that the initial peak in the 2012a event was unlikely to be due to a faint core-collapse SN. We propose that the high intrinsic luminosity of the latest peak, the variability history of SN 2009ip, and the detection of broad spectral lines indicative of high-velocity ejecta are consistent with a pulsational pair-instability event, and that the star may have survived the last outburst. The question of the survival of the LBV progenitor star and its future fate remain open issues, only to be answered with future monitoring of this historically unique explosion.
We present deep Chandra X-ray observations of two nearby Type Ia supernovae, SN 2017cbv and SN 2020nlb, which reveal no X-ray emission down to a luminosity $L_X$$lesssim$5.3$times$10$^{37}$ and $lesssim$5.4$times$10$^{37}$ erg s$^{-1}$ (0.3--10 keV), respectively, at $sim$16--18 days after the explosion. With these limits, we constrain the pre-explosion mass-loss rate of the progenitor system to be $dot{M}$$<$7.2$times$10$^{-9}$ and $<$9.7$times$10$^{-9}$ M$_{odot}$ yr$^{-1}$ for each (at a wind velocity $v_w$=100 km s$^{-1}$ and a radius of $R$$approx$10$^{16}$ cm), assuming any X-ray emission would originate from inverse Compton emission from optical photons up-scattered by the supernova shock. If the supernova environment was a constant density medium, we find a number density limit of n$_{CSM}$$<$36 and $<$65 cm$^{-3}$, respectively. These X-ray limits rule out all plausible symbiotic progenitor systems, as well as large swathes of parameter space associated with the single degenerate scenario, such as mass loss at the outer Lagrange point and accretion winds. We also present late-time optical spectroscopy of SN 2020nlb, and set strong limits on any swept up hydrogen ($L_{Halpha}$$<$2.7$times$10$^{37}$ ergs s$^{-1}$) and helium ($L_{He, lambda 6678}$$<$2.7$times$10$^{37}$ ergs s$^{-1}$) from a nondegenerate companion, corresponding to $M_{H}$$lesssim$0.7--2$times$10$^{-3}$ M$_{odot}$ and $M_{He}$$lesssim$4$times$10$^{-3}$ M$_{odot}$. Radio observations of SN 2020nlb at 14.6 days after explosion also yield a non-detection, ruling out most plausible symbiotic progenitor systems. While we have doubled the sample of normal type Ia supernovae with deep X-ray limits, more observations are needed to sample the full range of luminosities and sub-types of these explosions, and set statistical constraints on their circumbinary environments.
We propose that the energetic major outburst of the supernova (SN) impostor SN 2009ip in September 2012 (outburst 2012b) was a mergerburst event, where two massive stars merged. The previous outbursts of 2009 and 2011 might have occurred near periastron passages of the binary system prior to the merger, in a similar manner to the luminosity peaks in the nineteenth century Great Eruption of the massive binary system Eta Carinae. The major 2012b outburst and the 2012a pre-outburst, resemble the light curve of the mergerburst event V838 Mon. A merger of an evolved star with a mass of M1~60-100Mo and a secondary main sequence star of M2~0.2-0.5M1 can account for the energy of SN 2009ip and for the high velocities of the ejected gas. The ejected nebula is expected to have a non-spherical structure, e.g. bipolar or even a more complicated morphology.
We present observations of the interacting transient SN 2009ip, from the start of the outburst in October 2012 until the end of the 2012 observing season. The transient reached a peak of $M_V$=-17.7 mag before fading rapidly, with a total integrated luminosity of 1.9$times10^{49}$ erg over the period of August-December 2012. The optical and near infrared spectra are dominated by narrow emission lines, signaling a dense circumstellar environment, together with multiple components of broad emission and absorption in H and He at velocities between 0.5-1.2$times10^4$ km s$^{-1}$. We see no evidence for nucleosynthesized material in SN 2009ip, even in late-time pseudo-nebular spectra. We set a limit of $<$0.02 M$_{odot}$ on the mass of any synthesized $^{56}$Ni from the late time lightcurve. A simple model for the narrow Balmer lines is presented, and used to derive number densities for the circumstellar medium of between $sim 10^{9}-10^{10}$ cm$^{-3}$. Our near-infrared data does not show any excess at longer wavelengths. Our last data, taken in December 2012, shows that SN 2009ip has spectroscopically evolved to something quite similar to its appearance in late 2009, albeit with higher velocities. It is possible that neither of the eruptive and high luminosity events of SN 2009ip were induced by a core-collapse. We show that the peak and total integrated luminosity can be due to the efficient conversion of kinetic energy from colliding ejecta, and that around 0.05-0.1 M$_{odot}$ of material moving at 0.5-1$times10^4$ km s$^{-1}$ could comfortably produce the observed luminosity. The ejection of multiple shells, lack of evidence for nucleosynthesied elements and broad nebular lines, are all consistent with the pulsational-pair instability scenario. In this case the progenitor star may still exist, and will be observed after the current outburst fades.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
