Double-Peaked Balmer Emission Indicating Prompt Accretion Disk Formation in an X-Ray Faint Tidal Disruption Event

We present the multi-wavelength analysis of the tidal disruption event (TDE) AT~2018hyz (ASASSN-18zj). From follow-up optical spectroscopy, we detect the first unambiguous case of resolved double-peaked Balmer emission in a TDE. The distinct line profile can be well-modelled by a low eccentricity ($e\approx0.1$) accretion disk extending out to $\sim$100 $R_{p}$ and a Gaussian component originating from non-disk clouds, though a bipolar outflow origin cannot be completely ruled out. Our analysis indicates that in AT~2018hyz, disk formation took place promptly after the most-bound debris returned to pericenter, which we estimate to be roughly tens of days before the first detection. Redistribution of angular momentum and mass transport, possibly through shocks, must occur on the observed timescale of about a month to create the large \Ha-emitting disk that comprises $\lesssim$5\% of the initial stellar mass. With these new insights from AT~2018hyz, we infer that circularization is efficient in at least some, if not all optically-bright, X-ray faint TDEs. In these efficiently circularized TDEs, the detection of double-peaked emission depends on the disk inclination angle and the relative strength of the disk contribution to the non-disk component, possibly explaining the diversity seen in the current sample.Comment: 24 pages, 8 figures, 6 tables. Accepted for publication in Ap

Carnegie Supernova Project-I and -II: Measurements of H0H_0 using Cepheid, TRGB, and SBF Distance Calibration to Type Ia Supernovae

We present an analysis of Type Ia Supernovae (SNe~Ia) from both the Carnegie Supernova Project~I (CSP-I) and II (CSP-II), and extend the Hubble diagram from the optical to the near-infrared wavelengths ($uBgVriYJH$). We calculate the Hubble constant, $H_0$, using various distance calibrators: Cepheids, Tip of the Red Giant Branch (TRGB), and Surface Brightness Fluctuations (SBF). Combining all methods of calibrations, we derive $\rm H_0=71.76 \pm 0.58 \ (stat) \pm 1.19 \ (sys) \ km \ s^{-1} \ Mpc^{-1}$from$B$-band, and$\rm H_0=73.22 \pm 0.68 \ (stat) \pm 1.28 \ (sys) \ km \ s^{-1} \ Mpc^{-1}$from$H$-band. By assigning equal weight to the Cepheid, TRGB, and SBF calibrators, we derive the systematic errors required for consistency in the first rung of the distance ladder, resulting in a systematic error of$1.2\sim 1.3 \rm \ km \ s^{-1} \ Mpc^{-1}$in$H_0$. As a result, relative to the statistics-only uncertainty, the tension between the late-time$H_0$we derive by combining the various distance calibrators and the early-time$H_0$from the Cosmic Microwave Background is reduced. The highest precision in SN~Ia luminosity is found in the$Y$band ($0.12\pm0.01$mag), as defined by the intrinsic scatter ($\sigma_{int}$). We revisit SN~Ia Hubble residual-host mass correlations and recover previous results that these correlations do not change significantly between the optical and the near-infrared wavelengths. Finally, SNe~Ia that explode beyond 10 kpc from their host centers exhibit smaller dispersion in their luminosity, confirming our earlier findings. Reduced effect of dust in the outskirt of hosts may be responsible for this effect.Comment: Revised calculations are made. Will be resubmitted to Ap

Models of classroom assessment for course-based research experiences

Course-based research pedagogy involves positioning students as contributors to authentic research projects as part of an engaging educational experience that promotes their learning and persistence in science. To develop a model for assessing and grading students engaged in this type of learning experience, the assessment aims and practices of a community of experienced course-based research instructors were collected and analyzed. This approach defines four aims of course-based research assessment—(1) Assessing Laboratory Work and Scientific Thinking; (2) Evaluating Mastery of Concepts, Quantitative Thinking and Skills; (3) Appraising Forms of Scientific Communication; and (4) Metacognition of Learning—along with a set of practices for each aim. These aims and practices of assessment were then integrated with previously developed models of course-based research instruction to reveal an assessment program in which instructors provide extensive feedback to support productive student engagement in research while grading those aspects of research that are necessary for the student to succeed. Assessment conducted in this way delicately balances the need to facilitate students’ ongoing research with the requirement of a final grade without undercutting the important aims of a CRE education

BEAST OF YOUR ABSENCE

A collection of poetry that follows the death of a close friend and explores how grief devours the soul, and the ways in which we find strength to endure

X‑ray Crystallographic, Multifrequency Electron Paramagnetic Resonance, and Density Functional Theory Characterization of the Ni(P^Cy₂N^<i>t</i>Bu₂)₂^<i>n</i>+ Hydrogen Oxidation Catalyst in the Ni(I) Oxidation State

The Ni­(I) hydrogen oxidation catalyst [Ni­(P^Cy₂N^<i>t</i>Bu₂)₂]⁺ (<b>1</b>⁺; P^Cy₂N^<i>t</i>Bu₂ = 1,5-di­(<i>tert</i>-butyl)-3,7-dicyclohexyl-1,5-diaza-3,7-diphosphacyclooctane) has been studied using a combination of electron paramagnetic resonance (EPR) techniques (X-, Q-, and D-band, electron–nuclear double resonance, hyperfine sublevel correlation spectroscopy), X-ray crystallography, and density functional theory (DFT) calculations. Crystallographic and DFT studies indicate that the molecular structure of <b>1</b>⁺ is highly symmetrical. EPR spectroscopy has allowed determination of the electronic <b>g</b> tensor and the spin density distribution on the ligands, and revealed that the Ni­(I) center does not interact strongly with the potentially coordinating solvents acetonitrile and butyronitrile. The EPR spectra and magnetic parameters of <b>1</b>⁺ are found to be distinctly different from those for the related compound [Ni­(P^Ph₂N^Ph₂)₂]⁺ (<b>4</b>⁺). One significant contributor to these differences is that the molecular structure of <b>4</b>⁺ is unsymmetrical, unlike that of <b>1</b>⁺. DFT calculations on derivatives in which the R and R′ groups are systematically varied have allowed elucidation of structure/substituent relationships and their corresponding influence on the magnetic resonance parameters

X‑ray Crystallographic, Multifrequency Electron Paramagnetic Resonance, and Density Functional Theory Characterization of the Ni(P^Cy₂N^<i>t</i>Bu₂)₂^<i>n</i>+ Hydrogen Oxidation Catalyst in the Ni(I) Oxidation State

The Ni­(I) hydrogen oxidation catalyst [Ni­(P^Cy₂N^<i>t</i>Bu₂)₂]⁺ (<b>1</b>⁺; P^Cy₂N^<i>t</i>Bu₂ = 1,5-di­(<i>tert</i>-butyl)-3,7-dicyclohexyl-1,5-diaza-3,7-diphosphacyclooctane) has been studied using a combination of electron paramagnetic resonance (EPR) techniques (X-, Q-, and D-band, electron–nuclear double resonance, hyperfine sublevel correlation spectroscopy), X-ray crystallography, and density functional theory (DFT) calculations. Crystallographic and DFT studies indicate that the molecular structure of <b>1</b>⁺ is highly symmetrical. EPR spectroscopy has allowed determination of the electronic <b>g</b> tensor and the spin density distribution on the ligands, and revealed that the Ni­(I) center does not interact strongly with the potentially coordinating solvents acetonitrile and butyronitrile. The EPR spectra and magnetic parameters of <b>1</b>⁺ are found to be distinctly different from those for the related compound [Ni­(P^Ph₂N^Ph₂)₂]⁺ (<b>4</b>⁺). One significant contributor to these differences is that the molecular structure of <b>4</b>⁺ is unsymmetrical, unlike that of <b>1</b>⁺. DFT calculations on derivatives in which the R and R′ groups are systematically varied have allowed elucidation of structure/substituent relationships and their corresponding influence on the magnetic resonance parameters

\u3ci\u3eDrosophila\u3c/i\u3e Muller F Elements Maintain a Distinct Set of Genomic Properties Over 40 Million Years of Evolution

The Muller F element (4.2 Mb, ~80 protein-coding genes) is an unusual autosome of Drosophila melanogaster; it is mostly heterochromatic with a low recombination rate. To investigate how these properties impact the evolution of repeats and genes, we manually improved the sequence and annotated the genes on the D. erecta, D. mojavensis, and D. grimshawi F elements and euchromatic domains from the Muller D element. We find that F elements have greater transposon density (25–50%) than euchromatic reference regions (3–11%). Among the F elements, D. grimshawi has the lowest transposon density (particularly DINE-1: 2% vs. 11–27%). F element genes have larger coding spans, more coding exons, larger introns, and lower codon bias. Comparison of the Effective Number of Codons with the Codon Adaptation Index shows that, in contrast to the other species, codon bias in D. grimshawi F element genes can be attributed primarily to selection instead of mutational biases, suggesting that density and types of transposons affect the degree of local heterochromatin formation. F element genes have lower estimated DNA melting temperatures than D element genes, potentially facilitating transcription through heterochromatin. Most F element genes (~90%) have remained on that element, but the F element has smaller syntenic blocks than genome averages (3.4–3.6 vs. 8.4–8.8 genes per block), indicating greater rates of inversion despite lower rates of recombination. Overall, the F element has maintained characteristics that are distinct from other autosomes in the Drosophila lineage, illuminating the constraints imposed by a heterochromatic milieu