分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: A thermonuclear explosion triggered by a helium-shell detonation on a carbon-oxygen white dwarf core has been predicted to have strong UV line blanketing at early times due to the iron-group elements produced during helium-shell burning. We present the photometric and spectroscopic observations of SN 2016dsg, a sub-luminous peculiar Type I SN consistent with a thermonuclear explosion involving a thick He shell. With a redshift of 0.04, the $i$-band peak absolute magnitude is derived to be around -17.5. The object is located far away from its host, an early-type galaxy, suggesting it originated from an old stellar population. The spectra collected after the peak are unusually red, show strong UV line blanketing and weak O I $\lambda$7773 absorption lines, and do not evolve significantly over 30 days. An absorption line around 9700-10500 \AA is detected in the near-infrared spectrum and is likely from the unburnt helium in the ejecta. The spectroscopic evolution is consistent with the thermonuclear explosion models for a sub-Chandrasekhar mass white dwarf with a thick helium shell, while the photometric evolution is not well described by existing models.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: Optical time-domain surveys can unveil and characterize exciting but less-explored non-accreting and/or non-beaming neutron stars (NS) in binaries. Here we report the discovery of such a NS candidate using the LAMOST spectroscopic survey. The candidate, designated LAMOST J112306.9+400736 (hereafter J1123), is in a single-lined spectroscopic binary containing an optically visible M star. The star's large radial velocity variation and ellipsoidal variations indicate a relatively massive unseen companion. Utilizing follow-up spectroscopy from the Palomar 200-inch telescope and high-precision photometry from TESS, we measure a companion mass of $1.24_{-0.03}^{+0.03}~M_{\odot}$. Main-sequence stars with this mass are ruled out, leaving a NS or a massive white dwarf (WD). Although a massive WD cannot be ruled out, the lack of UV excess radiation from the companion supports the NS hypothesis. Deep radio observations with FAST yielded no detections of either pulsed or persistent emission. J1123 is not detected in numerous X-ray and gamma-ray surveys. These non-detections suggest that the NS candidate is not presently accreting and pulsing. Our work exemplifies the capability of discovering compact objects in non-accreting close binaries by synergizing the optical time-domain spectroscopy and high-cadence photometry.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: Optical time-domain surveys can unveil and characterize exciting but less-explored non-accreting and/or non-beaming neutron stars (NS) in binaries. Here we report the discovery of such a NS candidate using the LAMOST spectroscopic survey. The candidate, designated LAMOST J112306.9+400736 (hereafter J1123), is in a single-lined spectroscopic binary containing an optically visible M star. The star's large radial velocity variation and ellipsoidal variations indicate a relatively massive unseen companion. Utilizing follow-up spectroscopy from the Palomar 200-inch telescope and high-precision photometry from TESS, we measure a companion mass of $1.24_{-0.03}^{+0.03}~M_{\odot}$. Main-sequence stars with this mass are ruled out, leaving a NS or a massive white dwarf (WD). Although a massive WD cannot be ruled out, the lack of UV excess radiation from the companion supports the NS hypothesis. Deep radio observations with FAST yielded no detections of either pulsed or persistent emission. J1123 is not detected in numerous X-ray and gamma-ray surveys. These non-detections suggest that the NS candidate is not presently accreting and pulsing. Our work exemplifies the capability of discovering compact objects in non-accreting close binaries by synergizing the optical time-domain spectroscopy and high-cadence photometry.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: We report analysis using the James Webb Space Telescope (JWST) to identify a candidate progenitor star of the Type II-plateau supernova SN 2022acko in the nearby, barred spiral galaxy NGC 1300. To our knowledge, our discovery represents the first time JWST has been used to localize a progenitor system in pre-explosion archival Hubble Space Telescope (HST) images. We astrometrically registered a JWST NIRCam image from 2023 January, in which the SN was serendipitously captured, to pre-SN HST F160W and F814W images from 2017 and 2004, respectively. A star corresponding precisely to the SN position has been isolated with reasonable confidence, although a ~2.9 sigma difference exists between the measured position for the star from HST and the transformed SN position from JWST. That star has a spectral energy distribution and overall luminosity consistent with a single-star model having an initial mass somewhat less than the canonical 8 Msun theoretical threshold for core collapse, although the star's initial mass is inconsistent with that of a super-asymptotic giant branch star which might be a forerunner of an electron-capture SN. The properties of the progenitor alone imply that SN 2022acko is a relatively normal SN II-P, albeit most likely a low-luminosity one. The progenitor candidate should be confirmed with follow-up HST imaging at late times, when the SN has sufficiently faded. This potential use of JWST opens a new era of identifying SN progenitor candidates at high spatial resolution.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: We present photometric and spectroscopic data of SN 2018lab, a low luminosity type IIP supernova (LLSN) with a V-band peak luminosity of $-15.1\pm0.1$ mag. SN 2018lab was discovered by the Distance Less Than 40 Mpc (DLT40) SNe survey only 0.73 days post-explosion, as determined by observations from the Transiting Exoplanet Survey Satellite (TESS). TESS observations of SN 2018lab yield a densely sampled, fast-rising, early time light curve likely powered by circumstellar medium (CSM) interaction. The blue-shifted, broadened flash feature in the earliest spectra ($<$2 days) of SN 2018lab provide further evidence for ejecta-CSM interaction. The early emission features in the spectra of SN 2018lab are well described by models of a red supergiant progenitor with an extended envelope and close-in CSM. As one of the few LLSNe with observed flash features, SN 2018lab highlights the need for more early spectra to explain the diversity of flash feature morphology in type II SNe.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: Type Ia Supernovae are thermonuclear explosions of white dwarf stars. They play a central role in the chemical evolution of the Universe and are an important measure of cosmological distances. However, outstanding questions remain about their origins. Despite extensive efforts to obtain natal information from their earliest signals, observations have thus far failed to identify how the majority of them explode. Here, we present infant-phase detections of SN 2018aoz from a brightness of -10.5 absolute AB magnitudes -- the lowest luminosity early Type Ia signals ever detected -- revealing a hitherto unseen plateau in the $B$-band that results in a rapid redward color evolution between 1.0 and 12.4 hours after the estimated epoch of first light. The missing $B$-band flux is best-explained by line-blanket absorption from Fe-peak elements in the outer 1% of the ejected mass. The observed $B-V$ color evolution of the SN also matches the prediction from an over-density of Fe-peak elements in the same outer 1% of the ejected mass, whereas bluer colors are expected from a purely monotonic distribution of Fe-peak elements. The presence of excess nucleosynthetic material in the extreme outer layers of the ejecta points to enhanced surface nuclear burning or extended sub-sonic mixing processes in some normal Type Ia Supernova explosions.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: SN~2018aoz is a Type Ia SN with a $B$-band plateau and excess emission in the infant-phase light curves $\lesssim$ 1 day after first light, evidencing an over-density of surface iron-peak elements as shown in our previous study. Here, we advance the constraints on the nature and origin of SN~2018aoz based on its evolution until the nebular phase. Near-peak spectroscopic features show the SN is intermediate between two subtypes of normal Type Ia: Core-Normal and Broad-Line. The excess emission could have contributions from the radioactive decay of surface iron-peak elements as well as ejecta interaction with either the binary companion or a small torus of circumstellar material. Nebular-phase limits on H$\alpha$ and He~I favour a white dwarf companion, consistent with the small companion size constrained by the low early SN luminosity, while the absence of [O~I] and He~I disfavours a violent merger of the progenitor. Of the two main explosion mechanisms proposed to explain the distribution of surface iron-peak elements in SN~2018aoz, the asymmetric Chandrasekhar-mass explosion is less consistent with the progenitor constraints and the observed blueshifts of nebular-phase [Fe~II] and [Ni~II]. The helium-shell double-detonation explosion is compatible with the observed lack of C spectral features, but current 1-D models are incompatible with the infant-phase excess emission, $B_{\rm max}-V_{\rm max}$ color, and absence of nebular-phase [Ca~II]. Although the explosion processes of SN~2018aoz still need to be more precisely understood, the same processes could produce a significant fraction of Type Ia SNe that appear normal after $\sim$ 1 day.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: We present near-infrared (NIR) and optical observations of the Type Ic supernova (SN Ic) SN 2021krf obtained between days 13 and 259 at several ground-based telescopes. The NIR spectrum at day 68 exhibits a rising $K$-band continuum flux density longward of $\sim 2.0 \mu$m, which is likely from freshly formed dust in the SN ejecta. We estimate a carbon-grain dust mass of $\sim 2 \times 10^{-5}$ M$_{\odot}$ and a dust temperature of $\sim 900-1200$ K associated with this rising continuum and suggest the dust has formed in SN ejecta. Utilizing the one-dimensional multigroup radiation hydrodynamics code STELLA, we present two degenerate progenitor solutions for SN 2021krf, characterized by C-O star masses of 3.93 and 5.74 M$_{\odot}$, but with the same best-fit $^{56}$Ni mass of 0.11 M$_{\odot}$ for early times (0-70 days). At late times (70-300 days), optical light curves of SN 2021krf decline substantially more slowly than that expected from $^{56}$Co radioactive decay. A late-time optical spectrum on day 259 shows strong Ca II and [O I] ejecta lines from the SN. Lack of H and He lines in the late-time SN spectrum suggests the absence of significant interaction of the ejecta with the circumstellar medium. We reproduce the entire bolometric light curve with a combination of radioactive decay and an additional powering source in the form of a central engine of a millisecond pulsar with a magnetic field smaller than that of a typical magnetar.