Abstract
We present three epochs of early-time ultraviolet (UV) and optical HST/STIS spectroscopy of the young, nearby Type IIP supernova (SN) 2021yja. We complement the HST data with two earlier ...epochs of Swift UVOT spectroscopy. The HST and Swift UVOT spectra are consistent with those of other well-studied Type IIP SNe. The UV spectra exhibit rapid cooling at early times, while less dramatic changes are seen in the optical. We also present Lick/KAIT optical photometry up to the late-time tail phase, showing a very long plateau and shallow decline compared with other SNe IIP. Our modeling of the UV spectrum with the
TARDIS
radiative transfer code produces a good fit for a high-velocity explosion, a low total extinction
E
(
B
−
V
) = 0.07 mag, and a subsolar metallicity. We do not find a significant contribution to the UV flux from an additional heating source, such as interaction with the circumstellar medium, consistent with the observed flat plateau. Furthermore, the velocity width of the Mg
ii
λ
2798 line is comparable to that of the hydrogen Balmer lines, suggesting that the UV emission is confined to a region close to the photosphere.
Abstract
With
Cosmicflows-
4, distances are compiled for 55,877 galaxies gathered into 38,065 groups. Eight methodologies are employed, with the largest numbers coming from the correlations between ...the photometric and kinematic properties of spiral galaxies (TF) and elliptical galaxies (FP). Supernovae that arise from degenerate progenitors (type Ia SNe) are an important overlapping component. Smaller contributions come from distance estimates from the surface brightness fluctuations of elliptical galaxies and the luminosities and expansion rates of core-collapse supernovae (SNe II). Cepheid period–luminosity relation and tip of the red giant branch observations founded on local stellar parallax measurements along with the geometric maser distance to NGC 4258 provide the absolute scaling of distances. The assembly of galaxies into groups is an important feature of the study in facilitating overlaps between methodologies. Merging between multiple contributions within a methodology and between methodologies is carried out with Bayesian Markov chain Monte Carlo procedures. The final assembly of distances is compatible with a value of the Hubble constant of
H
0
= 74.6 km s
−1
Mpc
−1
with the small statistical error of ±0.8 km s
−1
Mpc
−1
but a large potential systematic error of ∼3 km s
−1
Mpc
−1
. Peculiar velocities can be inferred from the measured distances. The interpretation of the field of peculiar velocities is complex because of large errors on individual components and invites analyses beyond the scope of this study.
ABSTRACT
We present 637 low-redshift optical spectra collected by the Berkeley Supernova Ia Program (BSNIP) between 2009 and 2018, almost entirely with the Kast double spectrograph on the Shane 3 m ...telescope at Lick Observatory. We describe our automated spectral classification scheme and arrive at a final set of 626 spectra (of 242 objects) that are unambiguously classified as belonging to Type Ia supernovae (SNe Ia). Of these, 70 spectra of 30 objects are classified as spectroscopically peculiar (i.e. not matching the spectral signatures of ‘normal’ SNe Ia) and 79 SNe Ia (covered by 328 spectra) have complementary photometric coverage. The median SN in our final set has one epoch of spectroscopy, has a redshift of 0.0208 (with a low of 0.0007 and high of 0.1921), and is first observed spectroscopically 1.1 d after maximum light. The constituent spectra are of high quality, with a median signal-to-noise ratio of 31.8 pixel−1, and have broad wavelength coverage, with $\sim\! 95{{\ \rm per\ cent}}$ covering at least 3700–9800 Å. We analyse our data set, focusing on quantitative measurements (e.g. velocities, pseudo-equivalent widths) of the evolution of prominent spectral features in the available early-time and late-time spectra. The data are available to the community, and we encourage future studies to incorporate our spectra in their analyses.
The Type Ia supernova (SN Ia) 2017cfd in IC 0511 (redshift ) was discovered by the Lick Observatory Supernova Search 1.6 0.7 day after the fitted first-light time (15.2 days before B-band maximum ...brightness). Photometric and spectroscopic follow-up observations show that SN 2017cfd is a typical, normal SN Ia with a peak luminosity mag, Δm15(B) = 1.16 mag, and reached a B-band maximum ∼16.8 days after the first light. We estimate there to be moderately strong host-galaxy extinction (AV = 0.39 0.03 mag) based on MLCS2k2 fitting. The spectrum reveals a Si ii λ6355 velocity of ∼11,200 km s−1 at peak brightness. SN 2017cfd was discovered very young, with multiband data taken starting 2 days after the first light, making it a valuable complement to the currently small sample (fewer than a dozen) of SNe Ia with color data at such early times. We find that its intrinsic early-time color evolution belongs to the "blue" population rather than to the distinct "red" population. Using the photometry, we constrain the companion-star radius to be 2.5 R☉ with the Kasen model, thus ruling out a red-giant companion.
ABSTRACT
We present photometric and spectroscopic observations and analysis of SN 2021bxu (ATLAS21dov), a low-luminosity, fast-evolving Type IIb supernova (SN). SN 2021bxu is unique, showing a large ...initial decline in brightness followed by a short plateau phase. With $M_r = -15.93 \pm 0.16\, \mathrm{mag}$ during the plateau, it is at the lower end of the luminosity distribution of stripped-envelope supernovae (SE-SNe) and shows a distinct ∼10 d plateau not caused by H- or He-recombination. SN 2021bxu shows line velocities which are at least $\sim 1500\, \mathrm{km\, s^{-1}}$ slower than typical SE-SNe. It is photometrically and spectroscopically similar to Type IIb SNe during the photospheric phases of evolution, with similarities to Ca-rich IIb SNe. We find that the bolometric light curve is best described by a composite model of shock interaction between the ejecta and an envelope of extended material, combined with a typical SN IIb powered by the radioactive decay of 56Ni. The best-fitting parameters for SN 2021bxu include a 56Ni mass of $M_{\mathrm{Ni}} = 0.029^{+0.004}_{-0.005}\, \mathrm{{\rm M}_{\odot }}$, an ejecta mass of $M_{\mathrm{ej}} = 0.61^{+0.06}_{-0.05}\, \mathrm{{\rm M}_{\odot }}$, and an ejecta kinetic energy of $K_{\mathrm{ej}} = 8.8^{+1.1}_{-1.0} \times 10^{49}\, \mathrm{erg}$. From the fits to the properties of the extended material of Ca-rich IIb SNe we find a trend of decreasing envelope radius with increasing envelope mass. SN 2021bxu has MNi on the low end compared to SE-SNe and Ca-rich SNe in the literature, demonstrating that SN 2021bxu-like events are rare explosions in extreme areas of parameter space. The progenitor of SN 2021bxu is likely a low-mass He star with an extended envelope.
During the analysis of RR Lyrae stars (RRLs) discovered in the High Cadence Transient Survey (HiTS) taken with the Dark Energy Camera at the 4 m telescope at Cerro Tololo Inter-American Observatory, ...we found a group of three very distant, fundamental mode pulsator RR Lyrae (type ab). The location of these stars agrees with them belonging to the Leo V ultra-faint satellite galaxy, for which no variable stars have been reported to date. The heliocentric distance derived for Leo V based on these stars is 173 5 kpc. The pulsational properties (amplitudes and periods) of these stars locate them within the locus of the Oosterhoff II group, similar to most other ultra-faint galaxies with known RRLs. This serendipitous discovery shows that distant RRLs may be used to search for unknown faint stellar systems in the outskirts of the Milky Way.
Abstract
We report early-time ultraviolet (UV) and optical spectroscopy of the young, nearby Type II supernova (SN) 2022wsp obtained by the Hubble Space Telescope (HST)/STIS at about 10 and 20 days ...after the explosion. The SN 2022wsp UV spectra are compared to those of other well-observed Type II/IIP SNe, including the recently studied Type IIP SN 2021yja. Both SNe exhibit rapid cooling and similar evolution during early phases, indicating a common behavior among SNe II. Radiative-transfer modeling of the spectra of SN 2022wsp with the
TARDIS
code indicates a steep radial density profile in the outer layer of the ejecta, a solar metallicity, and a relatively high total extinction of
E
(
B
−
V
) = 0.35 mag. The early-time evolution of the photospheric velocity and temperature derived from the modeling agree with the behavior observed from other previously studied cases. The strong suppression of hydrogen Balmer lines in the spectra suggests interaction with a preexisting circumstellar environment could be occurring at early times. In the SN 2022wsp spectra, the absorption component of the Mg
ii
P Cygni profile displays a double-trough feature on day +10 that disappears by day +20. The shape is well reproduced by the model without fine-tuning the parameters, suggesting that the secondary blueward dip is a metal transition that originates in the SN ejecta.
Abstract Over recent decades, robotic (or highly automated) searches for supernovae (SNe) have discovered several thousand events, many of them in quite nearby galaxies (distances < 30 Mpc). Most of ...these SNe, including some of the best-studied events to date, were found before maximum brightness and have associated with them extensive follow-up photometry and spectroscopy. Some of these discoveries are so-called “SN impostors,” thought to be superoutbursts of luminous blue variable stars, although possibly a new, weak class of massive-star explosions. We conducted a Snapshot program with the Hubble Space Telescope (HST) and obtained images of the sites of 31 SNe and four impostors, to acquire late-time photometry through two filters. The primary aim of this project was to reveal the origin of any lingering energy for each event, whether it is the result of radioactive decay or, in some cases, ongoing late-time interaction of the SN shock with preexisting circumstellar matter, or the presence of a light echo. Alternatively, lingering faint light at the SN position may arise from an underlying stellar population (e.g., a host star cluster, companion star, or a chance alignment). The results from this study complement and extend those from Snapshot programs by various investigators in previous HST cycles.
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.
We report the discovery of distant RR Lyrae stars, including the most distant known in the Milky Way, using data taken in the g-band with the Dark Energy Camera as part of the High cadence Transient ...Survey (HiTS; 2014 campaign). We detect a total of 173 RR Lyrae stars over a ∼120 deg2 area, including both known RR Lyrae and new detections. The heliocentric distances dH of the full sample range from 9 to >200 kpc, with 18 of them beyond 90 kpc. We identify three sub-groups of RR Lyrae as members of known systems: the Sextans dwarf spheroidal galaxy, for which we report 46 new discoveries, and the ultra-faint dwarf galaxies Leo IV and Leo V. Following an MCMC methodology, we fit spherical and ellipsoidal profiles of the form (R) ∼ Rn to the radial density distribution of RR Lyrae in the Galactic halo. The best fit corresponds to the spherical case, for which we obtain a simple power-law index of , consistent with recent studies made with samples covering shorter distances. The pulsational properties of the outermost RR Lyrae in the sample (dH > 90 kpc) differ from the ones in the halo population at closer distances. The distribution of the stars in a period-amplitude diagram suggest they belong to Oosterhoff-intermediate or Oosterhoff II groups, similar to what is found in the ultra-faint dwarf satellites around the Milky Way. The new distant stars discovered represent an important addition to the few existing tracers of the Milky Way potential in the outer halo.
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