Abstract
We present a detailed spectral analysis of Type Iax SN 2011ay. Our spectra cover epochs between −3 and +19 d with respect to the maximum light in B band. This time range allows us to employ ...a so-called abundance tomography technique. The synthetic spectral fitting was made with the 1D Monte Carlo radiative transfer code tardis. In this paper, we describe our method to fit multiple epochs with a self-consistent, stratified atmospheric model. We compare our results to previously published syn++ models and the predictions of different explosion scenarios. Using a fixed density profile (exponential fit of W7), we find that a uniform abundance model cannot reproduce the spectral features before maximum light because of the emergence of excessively strong Fe lines. In our best-fitting tardis model, we find an abundance profile that separated into two different regimes: a well-mixed region under 10 000 km s−1 and a stratified region with decreasing IGE abundances above 10 000 km s−1. Based on a detailed comparative analysis, our conclusion is that the available pure deflagration models cannot fully explain either the observed properties of SN 2011ay or the results of our tardis modelling. Further examinations are necessary to find an adequate explanation for the origin of this object.
Abstract
We report spectropolarimetric observations of the Type Ia supernova (SN) SN 2021rhu at four epochs: −7, +0, +36, and +79 days relative to its
B
-band maximum luminosity. A ...wavelength-dependent continuum polarization peaking at 3890 ± 93 Å and reaching a level of
p
max
=
1.78
%
±
0.02
% was found. The peak of the polarization curve is bluer than is typical in the Milky Way, indicating a larger proportion of small dust grains along the sight line to the SN. After removing the interstellar polarization, we found a pronounced increase of the polarization in the Ca
ii
near-infrared triplet, from ∼0.3% at day −7 to ∼2.5% at day +79. No temporal evolution in high-resolution flux spectra across the Na
i
D and Ca
ii
H and K features was seen from days +39 to +74, indicating that the late-time increase in polarization is intrinsic to the SN as opposed to being caused by scattering of SN photons in circumstellar or interstellar matter. We suggest that an explanation for the late-time rise of the Ca
ii
near-infrared triplet polarization may be the alignment of calcium atoms in a weak magnetic field through optical excitation/pumping by anisotropic radiation from the SN.
The nearby SN 2017eaw is a Type II-P ("plateau") supernova (SN) showing early-time, moderate CSM interaction. We present a comprehensive study of this SN, including the analysis of high-quality ...optical photometry and spectroscopy covering the very early epochs up to the nebular phase, as well as near-ultraviolet and near-infrared spectra and early-time X-ray and radio data. The combined data of SNe 2017eaw and 2004et allow us to get an improved distance to the host galaxy, NGC 6946, of D ∼ 6.85 0.63 Mpc; this fits into recent independent results on the distance of the host and disfavors the previously derived (30% shorter) distances based on SN 2004et. From modeling the nebular spectra and the quasi-bolometric light curve, we estimate the progenitor mass and some basic physical parameters for the explosion and ejecta. Our results agree well with previous reports on a red supergiant progenitor star with a mass of ∼15-16 M . Our estimation of the pre-explosion mass-loss rate ( yr−1) agrees well with previous results based on the opacity of the dust shell enshrouding the progenitor, but it is orders of magnitude lower than previous estimates based on general light-curve modeling of Type II-P SNe. Combining late-time optical and mid-infrared data, a clear excess at 4.5 m can be seen, supporting the previous statements on the (moderate) dust formation in the vicinity of SN 2017eaw.
Abstract
The LIGO HET Response (LIGHETR) project is an enterprise to follow up optical transients (OTs) discovered as gravitational-wave merger sources by the LIGO/Virgo collaboration (LVC). Early ...spectroscopy has the potential to constrain crucial parameters such as the aspect angle. The LIGHETR collaboration also includes the capacity to model the spectroscopic evolution of mergers to facilitate a real-time direct comparison of models with our data. The principal facility is the Hobby–Eberly Telescope. LIGHETR uses the massively replicated VIRUS array of spectrographs to search for associated OTs and obtain early blue spectra, and in a complementary role, the low-resolution LRS2 spectrograph is used to obtain spectra of viable candidates as well as a densely sampled series of spectra of true counterparts. Once an OT is identified, the anticipated cadence of spectra would match or considerably exceed anything achieved for GW170817 = AT2017gfo for which there were no spectra in the first 12 hr and thereafter only roughly once daily. We describe special HET-specific software written to facilitate the program and attempts to determine the flux limits to undetected sources. We also describe our campaign to follow up OT candidates during the third observational campaign of the LIGO and Virgo Scientific Collaborations. We obtained VIRUS spectroscopy of candidate galaxy hosts for five LVC gravitational-wave events and LRS2 spectra of one candidate for the OT associated with S190901ap. We identified that candidate, ZTF19abvionh = AT2019pip, as a possible Wolf–Rayet star in an otherwise unrecognized nearby dwarf galaxy.
Abstract
2007 OR
10
is currently the third largest known dwarf planet in the trans-Neptunian region, with an effective radiometric diameter of ∼1535 km. It has a slow rotation period of ∼45 hr that ...was suspected to be caused by tidal interactions with a satellite undetected at that time. Here, we report on the discovery of a likely moon of 2007 OR
10
, identified on archival
Hubble Space Telescope
WFC3/UVIS system images. Although the satellite is detected at two epochs, this does not allow an unambiguous determination of the orbit and the orbital period. A feasible 1.5–5.8 · 10
21
kg estimate for the system mass leads to a likely 35–100 day orbital period. The moon is about 4.ͫ2 fainter than 2007 OR
10
in
HST
images that corresponds to a diameter of 237 km assuming equal albedos with the primary. Due to the relatively small size of the moon, the previous size and albedo estimates for the primary remains unchanged. With this discovery all trans-Neptunian objects larger than 1000 km are now known to harbor satellites, an important constraint for moon formation theories in the young solar system.
2007 OR{sub 10} is currently the third largest known dwarf planet in the trans-Neptunian region, with an effective radiometric diameter of ∼1535 km. It has a slow rotation period of ∼45 hr that was ...suspected to be caused by tidal interactions with a satellite undetected at that time. Here, we report on the discovery of a likely moon of 2007 OR{sub 10}, identified on archival Hubble Space Telescope WFC3/UVIS system images. Although the satellite is detected at two epochs, this does not allow an unambiguous determination of the orbit and the orbital period. A feasible 1.5–5.8 · 10{sup 21} kg estimate for the system mass leads to a likely 35–100 day orbital period. The moon is about 4.ͫ2 fainter than 2007 OR{sub 10} in HST images that corresponds to a diameter of 237 km assuming equal albedos with the primary. Due to the relatively small size of the moon, the previous size and albedo estimates for the primary remains unchanged. With this discovery all trans-Neptunian objects larger than 1000 km are now known to harbor satellites, an important constraint for moon formation theories in the young solar system.
We present new high-resolution spectroscopic observations (λ/Δλ≈40 000) of 18 bright northern Cepheids carried out at the David Dunlap Observatory in 1997. The measurements mainly extend those ...presented in Paper I of this series, adding three more stars (AW Per, SV Vul, T Mon). The spectra were obtained in the yellow-red spectral region in the interval of 5900 and 6660 Å, including strong lines of sodium D and Hα. New radial velocities determined with the cross-correlation technique and the bisector technique are presented. The new data are compared with those recently published by several groups. We found systematic differences between the spectroscopic and CORAVEL-type measurements as large as 1–3 km s−1 in certain phases. We performed Baade-Wesselink analysis for CK Cam discovered by the Hipparcos satellite. The resulting radius is 31±1 R⊙, which is in very good agreement with recent period-radius relation by Gieren, Moffett & Barnes III. It is shown that the systematic velocity differences do not affect the Baade-Wesselink radius more than 1 per cent for CK Cam. Observational pieces of evidence of possible velocity gradient affecting the individual line profiles are studied. The full-width at half minimum (FWHM) of the metallic lines, similarly to the velocity differences, shows a very characteristic phase dependence, illustrating the effect of global compression in the atmosphere. The smallest line widths always occur around the maximal radius, while the largest FWHM is associated with velocity reversal before the minimal radius. Three first overtone pulsators do not follow the general trend: the largest FWHM in SU Cas and SZ Tau occurs after the smallest radius, during the expansion, while in V1334 Cyg there are only barely visible FWHM variations. The possibility of a bright yellow companion of V1334 Cyg is briefly discussed. The observed line-profile asymmetries exceed the values predicted with a simple projection effect by a factor of 2–3. This could be associated with the velocity gradient, which is also supported by the differences between individual line velocities of different excitation potentials.
Abstract
We present follow-up photometric and spectroscopic observations, and subsequent analysis of Gaia20eae. This source triggered photometric alerts during 2020 after showing a ∼3 mag increase in ...its brightness. Its Gaia Alert light curve showed the shape of a typical eruptive young star. We carried out observations to confirm Gaia20eae as an eruptive young star and classify it. Its pre-outburst spectral energy distribution shows that Gaia20eae is a moderately embedded Class II object with
L
bol
= 7.22
L
⊙
. The color–color and color–magnitude diagrams indicate that the evolution in the light curve is mostly gray. Multiple epochs of the H
α
line profile suggest an evolution of the accretion rate and winds. The near-infrared spectra display several emission lines, a feature typical of EX Lupi-type (EXor) eruptive young stars. We estimated the mass accretion rate during the dimming phase to be
M
˙
= 3–8 × 10
−7
M
⊙
yr
−1
, higher than typical T Tauri stars of similar mass and comparable to other EXors. We conclude Gaia20eae is a new EXor-type candidate.
The interaction between the expanding supernova (SN) ejecta with the circumstellar material (CSM) that was expelled from the progenitor prior to explosion is a long-sought phenomenon, yet ...observational evidence is scarce. Here we confirm a new example: SN 2004dk, originally a hydrogen-poor, helium-rich Type Ib SN that reappeared as a strong -emitting point source on narrowband images. We present follow-up optical spectroscopy that reveals the presence of a broad component with full width at half maximum of ∼ 290 in addition to the narrow +N ii emission features from the host galaxy. Such a broad component is a clear sign of an ejecta-CSM interaction. We also present observations with the XMM-Newton Observatory, the Swift satellite, and the Chandra X-ray Observatory that span 10 days to 15 years after discovery. The detection of strong radio, X-ray, and emission years after explosion allows various constraints to be put on pre-SN mass-loss processes. We present a wind-bubble model in which the CSM is "pre-prepared" by a fast wind interacting with a slow wind. Much of the outer density profile into which the SN explodes corresponds to no steady-state mass-loss process. We estimate that the shell of compressed slow wind material was ejected ∼1400 yr prior to explosion, perhaps during carbon burning, and that the SN shock had swept up about 0.04 of material. The region emitting the has a density of order .
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