Abstract
We present photometry and spectroscopy of SN 2013fs and SN 2013fr in the first ∼100 d post-explosion. Both objects showed transient, relatively narrow H α emission lines characteristic of ...SNe IIn, but later resembled normal SNe II-P or SNe II-L, indicative of fleeting interaction with circumstellar material (CSM). SN 2013fs was discovered within 8 h of explosion; one of the earliest SNe discovered thus far. Its light curve exhibits a plateau, with spectra revealing strong CSM interaction at early times. It is a less luminous version of the transitional SN IIn PTF11iqb, further demonstrating a continuum of CSM interaction intensity between SNe II-P and SNe IIn. It requires dense CSM within 6.5 × 1014 cm of the progenitor, from a phase of advanced pre-SN mass loss beginning shortly before explosion. Spectropolarimetry of SN 2013fs shows little continuum polarization (∼0.5 per cent, consistent with zero), but noticeable line polarization during the plateau phase. SN 2013fr morphed from an SN IIn at early times to an SN II-L. After the first epoch, its narrow lines probably arose from host-galaxy emission, but the bright, narrow H α emission at early times may be intrinsic to the SN. As for SN 2013fs, this would point to a short-lived phase of strong CSM interaction if proven to be intrinsic, suggesting a continuum between SNe IIn and SNe II-L. It is a low-velocity SN II-L like SN 2009kr, but more luminous. SN 2013fr also developed an infrared excess at later times, due to warm CSM dust that requires a more sustained phase of strong pre-SN mass loss.
ABSTRACT
MCA-1B (also called UIT003) is a luminous hot star in the western outskirts of M33, classified over 20 yr ago with a spectral type of Ofpe/WN9 and identified then as a candidate luminous ...blue variable (LBV). Palomar Transient Factory data reveal that this star brightened in 2010, with a light curve resembling that of the classic LBV star AF And in M31. Other Ofpe/WN9 stars have erupted as LBVs, but MCA-1B was unusual because it remained hot. It showed a WN-type spectrum throughout its eruption, whereas LBVs usually get much cooler. MCA-1B showed an almost four-fold increase in bolometric luminosity and a doubling of its radius, but its temperature stayed ≳29 kK. As it faded, it shifted to even hotter temperatures, exhibiting a WN7/WN8-type spectrum, and doubling its wind speed. MCA-1B is reminiscent of some supernova impostors, and its location resembles the isolated environment of SN 2009ip. It is most similar to HD 5980 (in the Small Magellanic Cloud) and GR 290 (also in M33). Whereas these two LBVs exhibited B-type spectra in eruption, MCA-1B is the first clear case where a Wolf–Rayet (WR) spectrum persisted at all times. Together, MCA-1B, HD 5980, and GR 290 constitute a class of WN-type LBVs, distinct from S Doradus LBVs. They are most interesting in the context of LBVs at low metallicity, a possible post-LBV/WR transition in binaries, and as likely Type Ibn supernova progenitors.
ABSTRACT We present spectropolarimetric observations of the nearby Type Ia supernova SN 2014J in M82 over six epochs: +0, +7, +23, +51, +77, +109, and +111 days with respect to B-band maximum. The ...strong continuum polarization, which is constant with time, shows a wavelength dependence unlike that produced by linear dichroism in Milky Way dust. The observed polarization may be due entirely to interstellar dust or include a circumstellar scattering component. We find that the polarization angle aligns with the magnetic field of the host galaxy, arguing for an interstellar origin. Additionally, we confirm a peak in polarization at short wavelengths that would imply along the light of sight, in agreement with earlier polarization measurements. For illustrative purposes, we include a two-component fit to the continuum polarization of our +51-day epoch that combines a circumstellar scattering component with interstellar dust where scattering can account for over half of the polarization at 4000 Å. Upon removal of the interstellar polarization signal, SN 2014J exhibits very low levels of continuum polarization. Asymmetries in the distribution of elements within the ejecta are visible through moderate levels of time-variable polarization in accordance with the Si ii λ6355 absorption line. At maximum light, the line polarization reaches ∼0.6% and decreases to 1 week later. This feature also forms a loop on the plane, illustrating that the ion does not have an axisymmetric distribution. The observed polarization properties suggest that the explosion geometry of SN 2014J is generally spheroidal with a clumpy distribution of silicon.
The discovery of "hot Jupiters" very close to their parent stars confirmed that Jovian planets migrate inward via several potential mechanisms. We present empirical constraints on planet migration ...halting mechanisms. We compute-model density functions of close-in exoplanets in the orbital semi-major axis-stellar-mass plane to represent planet migration that is halted via several mechanisms, including the interior 1:2 resonance with themagnetospheric disk truncation radius, the interior 1:2 resonance with the dust sublimation radius, and several scenarios for tidal halting. We use a Bayesian analysis to assess the model success in reproducing empirical distributions of confirmed exoplanets and Kepler candidates that orbit interior to 0.1 AU. For Kepler candidates, which have a more restricted range in stellar-mass compared to confirmed planets, we are unable to discern between the tidal dissipation and magnetospheric disk truncation braking mechanisms at a statistically significant level. The power-law model favors exponents in the range of 0.38-0.9. This is larger than that predicted for tidal halting, which suggests that additional physics may be missing in the tidal halting theory.
The Kepler mission discovery of candidate transiting exoplanets (KOIs) enables a plethora of ensemble analyses of the architecture and properties of exoplanetary systems. We compare the observed ...transit durations of KOIs to a synthetic distribution generated from the known eccentricities of radial velocity (RV) discovered exoplanets. We find that the Kepler and RV distributions differ at a statistically significant level. We identify three related systematic trends that are likely due to errors in stellar radii, which in turn affect the inferred exoplanet radii and the distribution thereof, and prevent a valid analysis of the underlying ensemble eccentricity distribution. First, 15% of KOIs have transit durations >20% longer than the transit duration expected for an edge-on circular orbit, including 92 KOIs with transit durations >50% longer, when only a handful of such systems are expected. Second, the median transit duration is too long by up to ∼25%. Random errors of < 50% in the stellar radius are not adequate to account for these two trends. We identify that incorrect estimates of stellar metallicity and extinction could account for these anomalies, rather than astrophysical effects such as eccentric exoplanets improbably transiting near apastron. Third, we find that the median transit duration is correlated with stellar radius, when no such trend is expected. All three effects are still present, although less pronounced, when considering only multiple transiting KOI systems which are thought to have a low false-positive rate. Improved stellar parameters for KOIs are necessary for the validity of future ensemble tests of exoplanetary systems found by Kepler.
ABSTRACT
We present multi-epoch spectropolarimetry and spectra for a sample of 14 Type IIn supernovae (SNe IIn). We find that after correcting for likely interstellar polarization, SNe IIn commonly ...show intrinsic continuum polarization of 1–3 per cent at the time of peak optical luminosity, although a few show weaker or negligible polarization. While some SNe IIn have even stronger polarization at early times, their polarization tends to drop smoothly over several hundred days after peak. We find a tendency for the intrinsic polarization to be stronger at bluer wavelengths, especially at early times. While polarization from an electron scattering region is expected to be grey, scattering of SN light by dusty circumstellar material (CSM) may induce such a wavelength-dependent polarization. For most SNe IIn, changes in polarization degree and wavelength dependence are not accompanied by changes in the position angle, requiring that asymmetric pre-SN mass loss had a persistent geometry. While 2–3 per cent polarization is typical, about 30 per cent of SNe IIn have very low or undetected polarization. Under the simplifying assumption that all SN IIn progenitors have axisymmetric CSM (i.e. disc/torus/bipolar), then the distribution of polarization values we observe is consistent with similarly asymmetric CSM seen from a distribution of random viewing angles. This asymmetry has very important implications for understanding the origin of pre-SN mass loss in SNe IIn, suggesting that it was shaped by binary interaction.
In this dissertation, I use spectropolarimetry, spectroscopy, and photometry to study Type IIn supernovae (SNe IIn) and their progenitor environments. In Chapter 1, I first introduce why the ...environments of massive stars undergoing eruptive mass-loss are interesting to study. I then discuss the classification scheme for SNe and why SNe IIn are of particular importance when studying eruptive mass-loss from massive stars. I describe the benefits of polarization data and how to interpret it in the context of SNe IIn. Lastly, I discuss spectropolarimetric trends in all SNe so far, with an emphasis on results for SNe IIn.In Chapter 2, I show my analysis of pre-SN images over almost 12 years from the Katzman Automatic Imaging Telescope, searching for progenitor outbursts similar to those of SN~2009ip or ηCar. While no progenitor outbursts were detected, I was able to set limiting magnitudes in the pre-SN images which constrain how faint outbursts must have been in order for there to be no detection. Further, I was able to estimate the probability of detecting at least one outburst within the dataset to be ≥ 60% for each outburst template used, suggesting that outbursts are typically less luminous than ~—13 mag or are not common just prior to explosion. This work was published in Bilinski et al. (2015).In Chapter 3, I use spectropolarimetry, spectra, and photometry of SN 2012ab to study its environment. The lack of broad absorption features and the strong intermediate-width emission in Hα is indicative of circumstellar material (CSM) interaction. The spectral evolution for SN 2012ab proves to be interesting as it evolves from having a strong broad blueshifted peak in Hα to a late-time broad red wing with a truncated blue wing. This suggests that SN 2012ab interacted with CSM approaching us early on after explosion and then began to interact with CSM on the far side at later times. Spectropolarimetric results suggest that strong CSM interaction with significant asymmetry tangential to our line of sight turned on by day 76. Mass-loss estimates for SN 2012ab place it among other SNe IIn which likely arise from an LBV-like star in an eccentric binary system undergoing eruptive mass loss. This work was published in Bilinski et al. (2018).In Chapter 4, I use spectropolarimetry, spectra, and photometry of SN 2014ab to study its environment. The spectrum of SN 2014ab remains remarkably unchanged over the course of ~150 d, showing a consistently stronger blueshifted emission component in Hα. This implies obscuration by large dust grains, occultation by optically thick material, or asymmetry between the far and near side of the CSM interaction region. However, spectropolarimetry for SN 2014ab indicates a low polarization level at all epochs, suggesting nearly circular symmetry in the plane perpendicular to our line of sight. SN 2014ab is the first published example of a SN IIn where the polarization is very low, despite there being evidence for asymmetry along the line of sight. This work was published in Bilinski et al. (2020).In Chapter 5, I explore the collective spectropolarimetric properties for a sample of 14 SNe IIn. Past spectropolarimetric studies of SNe IIn have focused on a single object usually with a few epochs of spectropolarimetry at most. I find a tendency for the intrinsic polarization to drop smoothly over hundreds of days after peak and for the intrinsic polarization to be stronger at bluer wavelengths, especially in early epochs. I suggest that scattering of the SN light by dusty CSM may be the source of this wavelength-dependent polarization which is added to the polarization from electron scattering. Changes in the magnitude of the polarization and the wavelength dependence with time are not generally accompanied by changes in the position angle, suggesting a persistent axisymmetric geometry in the environment of SNe IIn. This result favors progenitors for SNe IIn that are undergoing binary interaction prior to death. This work will soon be submitted for publication in the Monthly Notices of the Royal Astronomical Society.
We searched through roughly 12 years of archival survey data acquired by the Katzman Automatic Imaging Telescope (KAIT) as part of the Lick Observatory Supernova Search in order to detect or place ...limits on possible progenitor outbursts of Type IIn supernovae (SNe IIn). The KAIT data base contains multiple pre-SN images for five SNe IIn (plus one ambiguous case of an SN IIn/imposter) within 50 Mpc. No progenitor outbursts are found using the false discovery rate statistical method in any of our targets. Instead, we derive limiting magnitudes (LMs) at the locations of the SNe. These LMs (typically reaching m
R
≈ 19.5 mag) are compared to outbursts of SN 2009ip and η Car, plus additional simulated outbursts. We find that the data for SN 1999el and SN 2003dv are of sufficient quality to rule out events ∼40 d before the main peak caused by initially faint SNe from blue supergiant precursor stars, as in the cases of SN 2009ip and SN 2010mc. These SNe IIn may thus have arisen from red supergiant progenitors, or they may have had a more rapid onset of circumstellar matter interaction. We also estimate the probability of detecting at least one outburst in our data set to be ≳60% for each type of the example outbursts, so the lack of any detections suggests that such outbursts are either typically less luminous (intrinsically or owing to dust) than ∼−13 mag, or not very common among SNe IIn within a few years prior to explosion.
ABSTRACT
We present multi-epoch spectropolarimetry of Type IIn supernova SN2017hcc, 16–391 d after explosion. Continuum polarization up to 6 per cent is observed during the first epoch, making SN ...2017hcc the most intrinsically polarized SN ever reported at visible wavelengths. During the first 29 d, when the polarization is strongest, the continuum polarization exhibits wavelength dependence that rises toward the blue, then becomes wavelength independent by day 45. The polarization drops rapidly during the first month, even as the flux is still climbing to peak brightness. None the less, unusually high polarization is maintained until day 68, at which point the polarization declines to levels comparable to those of previous well-studied SNe IIn. Only minor changes in position angle (PA) are measured throughout the evolution. The blue slope of the polarized continuum and polarized line emission during the first month suggests that an aspherical distribution of dust grains in pre-shock circumstellar material (CSM) is echoing the SN IIn spectrum and strongly influencing the polarization, while the subsequent decline during the wavelength-independent phase appears consistent with electron scattering near the SN/CSM interface. The persistence of the PA between these two phases suggests that the pre-existing CSM responsible for the dust scattering at early times is part of the same geometric structure as the electron-scattering region that dominates the polarization at later times. SN 2017hcc appears to be yet another, but more extreme, case of aspherical yet well-ordered CSM in Type IIn SNe, possibly resulting from pre-SN mass-loss shaped by a binary progenitor system.
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