General relativity
predicts that short-orbital-period binaries emit considerable amounts of gravitational radiation. The upcoming Laser Interferometer Space Antenna
(LISA) is expected to detect tens ...of thousands of such systems
but few have been identified
, of which only one
is eclipsing-the double-white-dwarf binary SDSS J065133.338+284423.37, which has an orbital period of 12.75 minutes. Here we report the discovery of an eclipsing double-white-dwarf binary system, ZTF J153932.16+502738.8, with an orbital period of 6.91 minutes. This system has an orbit so compact that the entire binary could fit within the diameter of the planet Saturn. The system exhibits a deep eclipse, and a double-lined spectroscopic nature. We see rapid orbital decay, consistent with that expected from general relativity. ZTF J153932.16+502738.8 is a strong source of gravitational radiation close to the peak of LISA's sensitivity, and we expect it to be detected within the first week of LISA observations, once LISA launches in approximately 2034.
While tidal disruption events (TDEs) have long been heralded as laboratories for the study of quiescent black holes, the small number of known TDEs and uncertainties in their emission mechanism have ...hindered progress toward this promise. Here we present 17 new TDEs that have been detected recently by the Zwicky Transient Facility along with Swift UV and X-ray follow-up observations. Our homogeneous analysis of the optical/UV light curves, including 22 previously known TDEs from the literature, reveals a clean separation of light-curve properties with spectroscopic class. The TDEs with Bowen fluorescence features in their optical spectra have smaller blackbody radii, lower optical luminosities, and higher disruption rates compared to the rest of the sample. The small subset of TDEs that show only helium emission lines in their spectra have the longest rise times, the highest luminosities, and the lowest rates. A high detection rate of Bowen lines in TDEs with small photometric radii could be explained by the high density that is required for this fluorescence mechanism. The stellar debris can provide a source for this dense material. Diffusion of photons through this debris may explain why the rise and fade timescale of the TDEs in our sample are not correlated. We also report, for the first time, the detection of soft X-ray flares from a TDE on ∼day timescales. Based on the fact that the X-ray flares peak at a luminosity similar to the optical/UV blackbody luminosity, we attribute them to brief glimpses through a reprocessing layer that otherwise obscures the inner accretion flow.
We present observations of ZTF18abfcmjw (SN2019dge), a helium-rich supernova with a fast-evolving light curve indicating an extremely low ejecta mass ( 0.33 M ) and low kinetic energy ( 1.3 × 1050 ...erg). Early-time (<4 days after explosion) photometry reveals evidence of shock cooling from an extended helium-rich envelope of ∼0.1 M located ∼1.2 × 1013 cm from the progenitor. Early-time He II line emission and subsequent spectra show signatures of interaction with helium-rich circumstellar material, which extends from 5 × 1013 cm to 2 × 1016 cm. We interpret SN2019dge as a helium-rich supernova from an ultra-stripped progenitor, which originates from a close binary system consisting of a mass-losing helium star and a low-mass main-sequence star or a compact object (i.e., a white dwarf, a neutron star, or a black hole). We infer that the local volumetric birth rate of 19dge-like ultra-stripped SNe is in the range of 1400-8200 Gpc − 3 yr − 1 (i.e., 2%-12% of core-collapse supernova rate). This can be compared to the observed coalescence rate of compact neutron star binaries that are not formed by dynamical capture.
The Kitt Peak Electron Multiplying CCD demonstrator Coughlin, Michael W; Dekany, Richard G; Duev, Dmitry A ...
Monthly notices of the Royal Astronomical Society,
05/2019, Volume:
485, Issue:
1
Journal Article
We present the discovery of an optical transient (OT) in Messier 51, designated M51 OT2019-1 (also ZTF 19aadyppr, AT 2019abn, ATLAS19bzl), by the Zwicky Transient Facility (ZTF). The OT rose over 15 ...days to an observed luminosity of Mr = −13 ( L = 9 × 106 L ), in the luminosity gap between novae and typical supernovae (SNe). Spectra during the outburst show a red continuum, Balmer emission with a velocity width of 400 km s−1, Ca ii and Ca ii emission, and absorption features characteristic of an F-type supergiant. The spectra and multiband light curves are similar to the so-called "SN impostors" and intermediate-luminosity red transients (ILRTs). We directly identify the likely progenitor in archival Spitzer Space Telescope imaging with a 4.5 m luminosity of M4.5 −12.2 mag and a 3.6-4.5 color redder than 0.74 mag, similar to those of the prototype ILRTs SN 2008S and NGC 300 OT2008-1. Intensive monitoring of M51 with Spitzer further reveals evidence for variability of the progenitor candidate at 4.5 in the years before the OT. The progenitor is not detected in pre-outburst Hubble Space Telescope optical and near-IR images. The optical colors during outburst combined with spectroscopic temperature constraints imply a higher reddening of E(B − V) 0.7 mag and higher intrinsic luminosity of Mr −14.9 mag ( L = 5.3 × 107 L ) near peak than seen in previous ILRT candidates. Moreover, the extinction estimate is higher on the rise than on the plateau, suggestive of an extended phase of circumstellar dust destruction. These results, enabled by the early discovery of M51 OT2019-1 and extensive pre-outburst archival coverage, offer new clues about the debated origins of ILRTs and may challenge the hypothesis that they arise from the electron-capture induced collapse of extreme asymptotic giant branch stars.
A central goal of group-based psychotherapy is for participants to gain insight into how they perceive others and how others perceive them. However, such interpersonal perceptions are challenging to ...study because any given perception could be a function of the perceiver (some people see everyone as friendly), the target (some people are seen as friendly by everyone), or both. The present article provides an introduction and brief tutorial for how the social relations model (SRM) can be applied to studying such interpersonal perceptions within psychotherapy groups. The SRM is a theoretical and statistical model for understanding the possible sources of dyadic perceptions and behaviors. Specifically, any interpersonal perception within a group can be partitioned into variance due to the person making the rating (perceiver effect), the target of the rating (target effect), the relationship between perceiver and target (relationship effect), and the group as a whole. Research on group psychotherapy is especially amenable to a SRM analysis because the interpersonal context allows multiple perceivers to rate multiple targets, which is a requirement of any SRM analysis. A fictitious study of wilderness therapy is used to highlight the conceptual, methodological, and statistical issues that are addressed with the SRM. Supplementary data and output files are provided to elucidate the analytic process using the WinSoReMo software. Although there are multiple ways that SRM studies and analyses can be conducted, the WinSoReMo program is specifically designed for round-robin data in which group members rate, and are rated by, other group members.
AbstractThe City of Atlanta plans to convert a recently acquired urban quarry into Bellwood Quarry Reservoir (BQR), an off-stream supplemental water supply. CE-QUAL-W2, Version 3.5, was used to ...perform five-year water quality simulations of the reservoir. Nine inflow/outflow design and operation scenarios were evaluated for thermal stratification, dissolved oxygen (DO), algae, and iron (Fe) and manganese (Mn). For a perpetual storage scenario with no inflow and outflow and an operating scenario with monthly pump exercising flows, the model predicts ample reservoir DO to maintain an oxidizing environment in the hypolimnion and low dissolved Fe and Mn. A single portal near the bottom of the reservoir is recommended for alternating pump exercise inflows and outflows. Continuous flow-through operating scenarios do not improve predicted water quality. However, if selected, a mid-depth inflow and bottom outflow design configuration is recommended. A natural monomictic cycle is essential to maintain hypolimnetic DO. BQR’s relatively large mean depth (60 m) and low sediment surface area to volume ratio is consistent with other mesotrophic lakes of similar water quality.
The Zwicky Transient Facility: Science Objectives Graham, Matthew J.; Barbarino, Cristina; Blagorodnova, Nadejda ...
Publications of the Astronomical Society of the Pacific,
07/2019, Volume:
131, Issue:
1001
Journal Article
Peer reviewed
Open access
The Zwicky Transient Facility (ZTF), a public-private enterprise, is a new time-domain survey employing a dedicated camera on the Palomar 48-inch Schmidt telescope with a 47 deg2 field of view and an ...8 second readout time. It is well positioned in the development of time-domain astronomy, offering operations at 10% of the scale and style of the Large Synoptic Survey Telescope (LSST) with a single 1-m class survey telescope. The public surveys will cover the observable northern sky every three nights in g and r filters and the visible Galactic plane every night in g and r. Alerts generated by these surveys are sent in real time to brokers. A consortium of universities that provided funding ("partnership") are undertaking several boutique surveys. The combination of these surveys producing one million alerts per night allows for exploration of transient and variable astrophysical phenomena brighter than r ∼ 20.5 on timescales of minutes to years. We describe the primary science objectives driving ZTF, including the physics of supernovae and relativistic explosions, multi-messenger astrophysics, supernova cosmology, active galactic nuclei, and tidal disruption events, stellar variability, and solar system objects.
The Zwicky Transient Facility: Observing System Dekany, Richard; Smith, Roger M.; Riddle, Reed ...
Publications of the Astronomical Society of the Pacific,
03/2020, Volume:
132, Issue:
1009
Journal Article
Peer reviewed
Open access
The Zwicky Transient Facility (ZTF) Observing System (OS) is the data collector for the ZTF project to study astrophysical phenomena in the time domain. ZTF OS is based upon the 48 inch aperture ...Schmidt-type design Samuel Oschin Telescope at the Palomar Observatory in Southern California. It incorporates new telescope aspheric corrector optics, dome and telescope drives, a large-format exposure shutter, a flat-field illumination system, a robotic bandpass filter exchanger, and the key element: a new 47-square-degree, 600 megapixel cryogenic CCD mosaic science camera, along with supporting equipment. The OS collects and delivers digitized survey data to the ZTF Data System (DS). Here, we describe the ZTF OS design, optical implementation, delivered image quality, detector performance, and robotic survey efficiency.
PDF
