SNe Ia play key roles in revealing the accelerating expansion of the universe, but our knowledge of their progenitors is still very limited. Here we report the discovery of a rigid dichotomy in ...circumstellar (CS) environments around two subclasses of SNe Ia as defined by their distinct photospheric velocities. For the SNe Ia with high photospheric velocities (HVs), we found a significant excess flux in blue light 60-100 days past maximum, while this phenomenon is absent for SNe with normal photospheric velocity. This blue excess can be attributed to light echoes by circumstellar dust located at a distance of about (1-2) × 1017 cm from the HV subclass. Moreover, we also found that the HV SNe Ia show systematically evolving Na i absorption line by performing a systematic search of variable Na i absorption lines in spectra of all SNe Ia, whereas this evolution is rarely seen in normal ones. The evolving Na i absorption can be modeled in terms of photoionization model, with the location of the gas clouds at a distance of about 2 × 1017 cm, in striking agreement with the location of CS dust inferred from B-band light-curve excess. These observations show clearly that the progenitors of HV subclass are likely from single-degenerate progenitor system (i.e., symbiotic binary), while the NV subclass may arise from double-degenerate system.
Abstract
In this paper, we present photometric and spectroscopic observations of the subluminous Type Ia supernova (SN Ia) 2012ij, which has an absolute
B
-band peak magnitude
M
B
,
max
=
−
17.95
±
...0.15
mag. The
B
-band light curve exhibits a fast postpeak decline with Δ
m
15
(
B
) = 1.86 ± 0.05 mag. All the
R
- and
I
/
i
-band light curves show a weak secondary peak/shoulder feature at about 3 weeks after the peak, like some transitional subclass of SNe Ia, which could result from an incomplete merger of near-infrared (NIR) double peaks. The spectra are characterized by Ti
ii
and strong Si
ii
λ
5972 absorption features that are usually seen in low-luminosity objects like SN 1999by. The NIR spectrum before maximum light reveals weak carbon absorption features, implying the existence of unburned materials. We compare the observed properties of SN 2012ij with those predicted by the sub-Chandrasekhar-mass and the Chandrasekhar-mass delayed-detonation models and find that both optical and NIR spectral properties can be explained to some extent by these two models. By comparing the secondary maximum features in the
I
and
i
bands, we suggest that SN 2012ij is a transitional object linking normal SNe Ia to typical 91bg-like ones. From the published sample of SNe Ia from the Carnegie Supernova Project II, we estimate that the fraction of SN 2012ij–like SNe Ia is not lower than ∼2%.
Abstract
We present extensive optical photometric and spectroscopic observations of the high-velocity (HV) Type Ia supernova (SN Ia) 2017fgc, covering the phase from ∼12 days before to ∼389 days ...after maximum brightness. SN 2017fgc is similar to normal SNe Ia, with an absolute peak magnitude of
M
max
B
≈
−19.32 ± 0.13 mag and a post-peak decline of Δ
m
15
(
B
) = 1.05 ± 0.07 mag. Its peak bolometric luminosity is derived as (1.32 ± 0.13) × 10
43
erg s
−1
, corresponding to a
56
Ni mass of 0.51 ± 0.03
M
⊙
. The light curves of SN 2017fgc are found to exhibit excess emission in the
UBV
bands in the early nebular phase and pronounced secondary shoulder/maximum features in the
RrIi
bands. Its spectral evolution is similar to that of HV SNe Ia, with a maximum-light Si
ii
velocity of 15,000 ± 150 km s
−1
and a post-peak velocity gradient of ∼120 ± 10 km s
−1
day
−1
. The Fe
ii
and Mg
ii
lines blended near 4300 Å and the Fe
ii
, Si
ii
, and Fe
iii
lines blended near 4800 Å are obviously stronger than those of normal SNe Ia. Inspecting a large sample reveals that the strength of the two blends in the spectra, and the secondary peak in the
i
/
r
-band light curves, are found to be positively correlated with the maximum-light Si
ii
velocity. Such correlations indicate that HV SNe Ia may experience more complete burning in the ejecta and/or that their progenitors have higher metallicity. Examining the birthplace environment of SN 2017fgc suggests that it likely arose from a stellar environment with young and high-metallicity populations.
Abstract
ASASSN-14ms may represent the most luminous Type Ibn supernova (SN Ibn) ever detected, with an absolute
U
-band magnitude brighter than −22.0 mag and a total bolometric luminosity >1.0 × 10
...44
erg s
−1
near maximum light. The early-time spectra of this SN are characterized by a blue continuum on which are superimposed narrow P Cygni profile lines of He
i
, suggesting the presence of slowly moving (∼1000 km s
−1
), He-rich circumstellar material (CSM). At 1–2 months after maximum brightness, the He
i
line profiles become only slightly broader, with blueshifted velocities of 2000–3000 km s
−1
, consistent with the CSM shell being continuously accelerated by the SN light and ejecta. Like most SNe Ibn, the light curves of ASASSN-14ms show rapid post-peak evolution, dropping by ∼7 mag in the
V
band over three months. Such a rapid post-peak decline and high luminosity can be explained by interaction between SN ejecta and helium-rich CSM of 0.9
M
⊙
at a distance of ∼10
15
cm. The CSM around ASASSN-14ms is estimated to originate from a pre-explosion event with a mass-loss rate of 6.7
M
⊙
yr
−1
(assuming a velocity of ∼1000 km s
−1
), which is consistent with abundant He-rich material violently ejected during the late Wolf–Rayet (WN9-11 or Opfe) stage. After examining the light curves for a sample of SNe Ibn, we find that the more luminous ones tend to have slower post-peak decline rates, reflecting that the observed differences may arise primarily from discrepancies in the CSM distribution around the massive progenitors.
Abstract We present optical observations and analysis of the bright type Iax supernova SN 2020udy hosted by NGC 0812. The evolution of the light curve of SN 2020udy is similar to that of other bright ...type Iax SNe. Analytical modeling of the quasi-bolometric light curves of SN 2020udy suggests that 0.08 ± 0.01 M ⊙ of 56 Ni would have been synthesized during the explosion. The spectral features of SN 2020udy are similar to those of the bright members of type Iax class, showing a weak Si ii line. The late-time spectral sequence is mostly dominated by iron group elements with broad emission lines. Abundance tomography modeling of the spectral time series of SN 2020udy using TARDIS indicates stratification in the outer ejecta; however, to confirm this, spectral modeling at a very early phase is required. After maximum light, uniform mixing of chemical elements is sufficient to explain the spectral evolution. Unlike in the case of normal type Ia SNe, the photospheric approximation remains robust until +100 days, requiring an additional continuum source. Overall, the observational features of SN 2020udy are consistent with the deflagration of a carbon–oxygen white dwarf.
Abstract
We have conducted photometric and spectroscopic observations of the peculiar Type Ia supernova (SN Ia) 2016ije that was discovered through the Tsinghua-NAOC Transient Survey. This peculiar ...object exploded in the outskirts of a metal-poor, low-surface brightness galaxy (i.e.,
M
g
= −14.5 mag). Our photometric analysis reveals that SN 2016ije is subluminous (
M
B
,
max
= −17.65 ± 0.06 mag) but exhibits relatively broad light curves (Δ
m
15
(
B
) = 1.35 ± 0.14 mag), similar to the behavior of SN 2002es. Our analysis of the bolometric light curve indicates that only 0.14 ± 0.04
M
⊙
of
56
Ni was synthesized in the explosion of SN 2016ije, which suggests a less energetic thermonuclear explosion when compared to normal SNe Ia, and this left a considerable amount of unburned materials in the ejecta. Spectroscopically, SN 2016ije resembles other SN 2002es-like SNe Ia, except that the ejecta velocity inferred from its carbon absorption line (∼4500 km s
−1
) is much lower than that from silicon lines (∼8300 km s
−1
) at around the maximum light. Additionally, most of the absorption lines are broader than other 02es-like SNe Ia. These peculiarities suggest the presence of significant unburned carbon in the inner region and a wide line-forming region along the line of sight. These characteristics suggest that SN 2016ije might originate from the violent merger of a white dwarf binary system, when viewed near an orientation along the iron-group-element cavity caused by the companion star.
ABSTRACT We present a comprehensive photometric and spectroscopic analysis of the short-period (∼5.32 h) and low-mass eclipsing binary TMTSJ0803 discovered by Tsinghua-Ma Huateng Telescope for Survey ...(TMTS). By fitting the light curves and radial velocity data with the Wilson–Devinney code, we find that the binary is composed of two late spotted active M dwarfs below the fully convective boundary. This is supported by the discovery of a significant Balmer emission lines in the LAMOST spectrum and prominent coronal X-ray emission. In comparison with the typical luminosity of rapidly rotating fully convective stars, the much brighter X-ray luminosity (LX/Lbol = 0.0159 ± 0.0059) suggests the stellar magnetic activity of fully convective stars could be enhanced in such a close binary system. Given the metallicity of M/H = − 0.35 dex as inferred from the LAMOST spectrum, we measure the masses and radii of both stars to be M1 = 0.169 ± 0.010 M⊙, M2 = 0.162 ± 0.016 M⊙, R1 = 0.170 ± 0.006 R⊙, and R2 = 0.156 ± 0.006 R⊙, respectively. Based on the luminosity ratio from the light-curve modelling, the effective temperatures of two components are also estimated. In comparison with the stellar evolution models, the radii, and effective temperatures of two components are all below the isochrones. The radius deflation might be mainly biased by a small radial velocity (RV) data or (and) a simple correction on RVs, while the discrepancy in effective temperature might be due to the enhanced magnetic activity in this binary.
ABSTRACT
Periodic variables are always of great scientific interest in astrophysics. Thanks to the rapid advancement of modern large-scale time-domain surveys, the number of reported variable stars ...has experienced substantial growth for several decades, which significantly deepened our comprehension of stellar structure and binary evolution. The Tsinghua University-Ma Huateng Telescopes for Survey (TMTS) has started to monitor the LAMOST sky areas since 2020, with a cadence of 1 min. During the period from 2020 to 2022, this survey has resulted in densely sampled light curves for ~30 000 variables of the maximum powers in the Lomb–Scargle periodogram above the 5σ threshold. In this paper, we classified 11 638 variable stars into six main types using xgboost and Random Forest classifiers with accuracies of 98.83 per cent and 98.73 per cent, respectively. Among them, 5301 (45.55 per cent) variables are newly discovered, primarily consisting of δ Scuti stars, demonstrating the capability of TMTS in searching for short-period variables. We cross-matched the catalogue with Gaia’s second Data Release and LAMOST’s seventh Data Release to obtain important physical parameters of the variables. We identified 5504 δ Scuti stars (including 4876 typical δ Scuti stars and 628 high-amplitude δ Scuti stars), 5899 eclipsing binaries (including EA-, EB-, and EW-type), and 226 candidates of RS Canum Venaticorum. Leveraging the metal abundance data provided by LAMOST and the Galactic latitude, we discovered eight candidates of SX Phe stars within the class of ‘δ Scuti stars’. Moreover, with the help of Gaia colour–magnitude diagram, we identified nine ZZ Ceti stars.
ABSTRACT
Late-time spectra of Type Ia supernovae (SNe Ia) are important in clarifying the physics of their explosions, as they provide key clues to the inner structure of the exploding white dwarfs. ...We examined late-time optical spectra of 36 SNe Ia, including five from our own project (SNe 2019np, 2019ein, 2021hpr, 2021wuf, and 2022hrs), with phase coverage of ∼200 to ∼400 d after maximum light. At this late phase, the outer ejecta have become transparent and the features of inner iron-group elements emerge in the spectra. Based on multicomponent Gaussian fits and reasonable choices for the pseudo-continuum around Ni and Fe emission features, we get reliable estimates of the Ni to Fe ratio, which is sensitive to the explosion models of SNe Ia. Our results show that the majority (about 67 per cent) of our SNe Ia are more consistent with the sub-Chandrasekhar-mass (i.e. double-detonation) model, although they could be affected by evolutionary or ionization effects. Moreover, we find that the Si ii λ6355 velocity measured around the time of maximum light tends to increase with the Ni to Fe ratio for the subsample with either redshifted or blueshifted nebular velocities, suggesting that progenitor metallicity might play an important role in accounting for the observed velocity diversity of SNe Ia.
The 2-m aperture Chinese Space Station Telescope (CSST), which observes at wavelengths ranging from 255 to 1000 nm, is expected to start science operations in 2024. An ultra-deep field observation ...program covering approximately 10 deg
2
is proposed with supernovae (SNe) and other transients as one of its primary science drivers. This paper presents the simulated detection results of type Ia supernovae (SNe Ia) and explores the impact of new datasets on the determinations of cosmological parameters. The simulated observations are conducted with an exposure time of 150 s and cadences of 10, 20, and 30 d. The survey mode covering a total of 80 observations but with a random cadence in the range of 4 to 14 d is also explored. Our simulation results indicate that the CSST can detect up to ∼ 1800 SNe Ia at
z
< 1.3. The simulated SNe Ia are then used to constrain the cosmological parameters. The constraint on Ω
m
can be improved by 37.5% using the 10-d cadence sample in comparison with the Pantheon sample. A deeper measurement simulation with a 300 s exposure time together with the Pantheon sample improves the current constraints on Ω
m
by 58.3% and
ω
by 47.7%. Taking future lager sets of nearby SN Ia sample form ground-based surveys (i.e.,
N
∼ 3400) into consideration, the constraints on
ω
can be improved by 59.1%. The CSST ultra-deep field observation program is expected to discover large amounts of SNe Ia over a broad redshift span and enhance our understanding of the nature of dark energy.
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