155 research outputs found
Optical observations of a SN 2002cx-like peculiar supernova SN 2013en in UGC 11369
We present optical observations of a SN 2002cx-like supernova SN 2013en in
UGC 11369, spanning from a phase near maximum light (t= +1 d) to t= +60 d with
respect to the R-band maximum. Adopting a distance modulus of mu=34.11 +/- 0.15
mag and a total extinction (host galaxy+Milky Way) of mag, we
found that SN 2013en peaked at mag, which is underluminous
compared to the normal SNe Ia. The near maximum spectra show lines of Si II, Fe
II, Fe III, Cr II, Ca II and other intermediate-mass and iron group elements
which all have lower expansion velocities (i.e., ~ 6000 km/s). The photometric
and spectroscopic evolution of SN 2013en is remarkably similar to those of SN
2002cx and SN 2005hk, suggesting that they are likely to be generated from a
similar progenitor scenario or explosion mechanism.Comment: 8 pages, 8 figures, 3 tables, accepted for publication in MNRA
The Progenitor of Supernova 2004dj in a Star Cluster
The progenitor of type II-plateau supernova (SN) 2004dj is identified with a
supergiant in a compact star cluster known as "Sandage Star 96" (S96) in the
nearby spiral galaxy NGC 2403, which was fortuitously imaged as part of the
Beijing-Arizona-Taiwan-Connecticut (BATC) Multicolor Sky Survey from Feb 1995
to Dec 2003 prior to SN 2004dj. The superior photometry of BATC images for S96,
taken with 14 intermediate-band filters covering 3000-10000\AA, unambiguously
establishes the star cluster nature of S96 with an age of Myr, a
reddening of mag and a total mass of M. The compact star cluster nature of S96 is also consistent
with the lack of light variations in the past decade. The SN progenitor is
estimated to have a main-sequence mass of 12M. The comparison
of our intermediate-band data of S96 with the post-outburst photometry obtained
as the SN has significantly dimmed, may hopefully conclusively establish the
nature of the progenitor.Comment: 4 pages; 3 figures. To accept for Publications in ApJ Letters, but
slightly longer in this perprin
Photometry of Variable Stars from THU-NAOC Transient Survey I: The First 2 Years
In this paper, we report the detections of stellar variabilities from the
first 2-year observations of sky area of about 1300 square degrees from the
Tsinghua University-NAOC Transient Survey (TNTS). A total of 1237 variable
stars (including 299 new ones) were detected with brightness < 18.0 mag and
magnitude variation >= 0.1 mag on a timescale from a few hours to few hundred
days. Among such detections, we tentatively identified 661 RR Lyrae stars, 431
binaries, 72 Semiregular pulsators, 29 Mira stars, 11 slow irregular variables,
11 RS Canum Venaticorum stars, 7 Gamma Doradus stars, 5 long period variables,
3 W Virginis stars, 3 Delta Scuti stars, 2 Anomalous Cepheids, 1 Cepheid, and 1
nove-like star based on their time-series variability index Js and their phased
diagrams. Moreover, we found that 14 RR Lyrae stars show the Blazhko effect and
67 contact eclipsing binaries exhibit the O'Connell effect. Since the period
and amplitude of light variations of RR Lyrae variables depend on their
chemical compositions, their photometric observations can be used to
investigate distribution of metallicity along the direction perpendicular to
the Galactic disk. We find that the metallicity of RR Lyrae stars shows large
scatter at regions closer to the Galactic plane (e.g., -3.0 < [Fe/H] < 0) but
tends to converge at [Fe/H]~ -1.7 at larger Galactic latitudes. This variation
may be related to that the RRAB Lyrae stars in the Galactic halo come from
globular clusters with different metallicity and vertical distances, i.e. OoI
and OoII populations, favoring for the dual-halo model.Comment: 18 pages, 19 figures, published in AJ, 150, 10
Revealing the Biexciton and Trion-exciton Complexes in BN Encapsulated WSe2
Strong Coulomb interactions in single-layer transition metal dichalcogenides
(TMDs) result in the emergence of strongly bound excitons, trions and
biexcitons. These excitonic complexes possess the valley degree of freedom,
which can be exploited for quantum optoelectronics. However, in contrast to the
good understanding of the exciton and trion properties, the binding energy of
the biexciton remains elusive, with theoretical calculations and experimental
studies reporting discrepant results. In this work, we resolve the conflict by
employing low-temperature photoluminescence spectroscopy to identify the
biexciton state in BN encapsulated single-layer WSe2. The biexciton state only
exists in charge neutral WSe2, which is realized through the control of
efficient electrostatic gating. In the lightly electron-doped WSe2, one free
electron binds to a biexciton and forms the trion-exciton complex. Improved
understanding of the biexciton and trion-exciton complexes paves the way for
exploiting the many-body physics in TMDs for novel optoelectronics
applications
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