12 research outputs found
Synthetic Light Curves of Shocked Dense Circumstellar Shells
We numerically investigate light curves (LCs) of shocked circumstellar shells
which are suggested to reproduce the observed LC of superluminous SN 2006gy
analytically. In the previous analytical model, the effects of the
recombination and the bolometric correction on LCs are not taken into account.
To see the effects, we perform numerical radiation hydrodynamic calculations of
shocked shells by using STELLA, which can numerically treat multigroup
radiation transfer with realistic opacities. We show that the effects of the
recombination and the bolometric correction are significant and the analytical
model should be compare to the bolometric LC instead of a single band LC. We
find that shocked circumstellar shells have a rapid LC decline initially
because of the adiabatic expansion rather than the luminosity increase and the
shocked shells fail to explain the LC properties of SN 2006gy. However, our
synthetic LCs are qualitatively similar to those of superluminous SN 2003ma and
SN 1988Z and they may be related to shocked circumstellar shells.Comment: 7 pages, 7 figures, 1 table, accepted by Monthly Notices of the Royal
Astronomical Societ
Supernovae from Red Supergiants with Extensive Mass Loss
We calculate multicolor light curves (LCs) of supernovae (SNe) from red
supergiants (RSGs) exploded within dense circumstellar medium (CSM). Multicolor
LCs are calculated by using a multi-group radiation hydrodynamics code STELLA.
If CSM is dense enough, the shock breakout signal is delayed and smeared by CSM
and kinetic energy of SN ejecta is efficiently converted to thermal energy
which is eventually released as radiation. We find that explosions of RSGs are
affected by CSM in early epochs when mass-loss rate just before the explosions
is higher than 10^{-4} Msun/yr. Their characteristic features are that the LC
has a luminous round peak followed by a flat LC, that multicolor LCs are
simultaneously bright in ultraviolet and optical at the peak, and that
photospheric velocity is very low at these epochs. We calculate LCs for various
CSM conditions and explosion properties, i.e., mass-loss rates, radii of CSM,
density slopes of CSM, explosion energies of SN ejecta, and SN progenitors
inside, to see their influence on LCs. We compare our model LCs to those of
ultraviolet-bright Type IIP SN 2009kf and show that the mass-loss rate of the
progenitor of SN 2009kf just before the explosion is likely to be higher than
10^{-4} Msun/yr. Combined with the fact that SN 2009kf is likely to be an
energetic explosion and has large 56Ni production, which implies that the
progenitor of SN 2009kf is a massive RSG, our results indicate that there could
be some mechanism to induce extensive mass loss in massive RSGs just before
their explosions.Comment: 16 pages, 17 figures, 3 tables, accepted by Monthly Notices of the
Royal Astronomical Society, the unit of Lbol in Table 3 corrected in v
The rise-time of Type II supernovae
We investigate the early-time light curves of a large sample of 223 Type II supernovae (SNe II) from the Sloan Digital Sky Survey and the Supernova Legacy Survey. Having a cadence of a few days and sufficient non-detections prior to explosion, we constrain risetimes, i.e. the durations from estimated first to maximum light, as a function of effective wavelength. At rest-frame g' band (λeff = 4722 Å), we find a distribution of fast rise-times with median of (7.5 ± 0.3) d. Comparing these durations with analytical shock models of Rabinak &Waxman and Nakar & Sari, and hydrodynamical models of Tominaga et al., which are mostly sensitive to progenitor radius at these epochs, we find a median characteristic radius of less than 400 solar radii. The inferred radii are on average much smaller than the radii obtained for observed red supergiants (RSG). Investigating the post-maximum slopes as a function of effective wavelength in the light of theoretical models, we find that massive hydrogen envelopes are still needed to explain the plateaus of SNe II. We therefore argue that the SN II rise-times we observe are either (a) the shock cooling resulting from the core collapse of RSG with small and dense envelopes, or (b) the delayed and prolonged shock breakout of the collapse of an RSG with an extended atmosphere or embedded within pre-SN circumstellar material.Instituto de Astrofísica de La PlataFacultad de Ciencias Astronómicas y Geofísica
Survey of Period Variations of Superhumps in SU UMa-Type Dwarf Novae
We systematically surveyed period variations of superhumps in SU UMa-type
dwarf novae based on newly obtained data and past publications. In many
systems, the evolution of superhump period are found to be composed of three
distinct stages: early evolutionary stage with a longer superhump period,
middle stage with systematically varying periods, final stage with a shorter,
stable superhump period. During the middle stage, many systems with superhump
periods less than 0.08 d show positive period derivatives. Contrary to the
earlier claim, we found no clear evidence for variation of period derivatives
between superoutburst of the same object. We present an interpretation that the
lengthening of the superhump period is a result of outward propagation of the
eccentricity wave and is limited by the radius near the tidal truncation. We
interpret that late stage superhumps are rejuvenized excitation of 3:1
resonance when the superhumps in the outer disk is effectively quenched. Many
of WZ Sge-type dwarf novae showed long-enduring superhumps during the
post-superoutburst stage having periods longer than those during the main
superoutburst. The period derivatives in WZ Sge-type dwarf novae are found to
be strongly correlated with the fractional superhump excess, or consequently,
mass ratio. WZ Sge-type dwarf novae with a long-lasting rebrightening or with
multiple rebrightenings tend to have smaller period derivatives and are
excellent candidate for the systems around or after the period minimum of
evolution of cataclysmic variables (abridged).Comment: 239 pages, 225 figures, PASJ accepte
The Circumstellar Material around the Type IIP SN 2021yja
International audienceThe majority of Type II-plateau supernovae (SNe IIP) have light curves that are not compatible with the explosions of stars in a vacuum; instead, the light curves require the progenitors to be embedded in circumstellar matter (CSM). We report on the successful fitting of the well-observed SN IIP 2021yja as a core-collapse explosion of a massive star with an initial mass of ∼15 M and a pre-explosion radius of 631 R. To explain the early-time behavior of the broadband light curves, the presence of 0.55 M CSM within ∼2 × 10 cm is needed. Like many other SNe IIP, SN 2021yja exhibits an early-time flux excess including ultraviolet wavelengths. This, together with the short rise time (<2 days) in the gri bands, indicates the presence of a compact component in the CSM, essentially adjacent to the progenitor. We discuss the origin of the preexisting CSM, which is most likely a common property of highly convective red supergiant envelopes. We argue that the difficulty in fitting the entire light curve with one spherical distribution indicates that the CSM around the SN 2021yja progenitor was asymmetric
Research agenda for the Russian Far East and utilization of multi-platform comprehensive environmental observations
The Russian Far East is a region between China and the Russian Arctic with a diverse climatological, geophysical, oceanic, and economical characteristic. The southern region is located in the Far East monsoon sector, while the northern parts are affected by the Arctic Ocean and cold air masses penetrating far to the south. Growing economic activities and traffic connected to the China Belt and Road Initiative together with climate change are placing an increased pressure upon the Russian Far East environment. There is an urgent need to improve the capacity to measure the atmospheric and environmental pollution and analyze their sources and to quantify the relative roles of local and transported pollution emissions in the region. In the paper, we characterize the current environmental and socio-economical landscape of the Russian Far East and summarize the future climate scenarios and identify the key regional research questions. We discuss the research infrastructure concept, which is needed to answer the identified research questions. The integrated observations, filling in the critical observational gap at the Northern Eurasian context, are required to provide state-of-the-art observations and enable follow-up procedures that support local, regional, and global decision making in the environmental context.Peer reviewe