We explore the consequences of dynamical evolution of field binaries composed of a primary black hole (BH) and aWolf-Rayet (WR) star in the context of gravitational wave (GW) source progenitors. We argue, from general considerations, that the spin of the WR-descendent BH will be maximal in a significant number of cases due to dynamical effects. In other cases, the spin should reflect the natal spin of the primary BH which is currently theoretically unconstrained. We argue that the three currently published LIGO systems (GW150914, GW151226, LVT151012) suggest that this spin is small. The resultant effective spin distribution of gravitational wave sources should thus be bi-model if this classic GW progenitor channel is indeed dominant. While this is consistent with the LIGO detections thus far, it is in contrast to the three best-measured high-mass X-ray binary (HMXB) systems. A comparison of the spin distribution of HMXBs and GW sources should ultimately reveal whether or not these systems arise from similar astrophysical channels.

Swope Supernova Survey 2017a (SSS17a) was discovered as the first optical counterpart to the gravitational wave event GW170817. Although its light curve on the timescale of weeks roughly matches the expected luminosity and red color of an r-process powered transient, the explanation for the blue emission from high velocity material over the first few days is not as clear. Here we show that the power-law evolution of the luminosity, temperature, and photospheric radius during these early times can be explained by cooling of shock-heated material around the neutron star merger. This heating is likely from the interaction of the gamma-ray burst jet with merger debris, the so-called cocoon emission. We summarize the properties of this emission and provide formulae that can be used to study future detections of shock cooling from merging neutron stars. This argues that optical transient surveys should search for such early, blue light if they wish to find off-axis gamma-ray bursts and double neutron star gravitational wave events as soon as possible after the merger.

We present a new method for calculating loops in cosmological perturbation theory. This method is based on approximating a ACDM-like cosmology as a finite sum of complex power-law universes. The decomposition is naturally achieved using an FFTLog algorithm. For power-law cosmologies, all loop integrals are formally equivalent to loop integrals of massless quantum field theory. These integrals have analytic solutions in terms of generalized hypergeometric functions. We provide explicit formulae for the one-loop and the two-loop power spectrum and the one-loop bispectrum. A chief advantage of our approach is that the difficult part of the calculation is cosmology independent, need be done only once, and can be recycled for any relevant predictions. Evaluation of standard loop diagrams then boils down to a simple matrix multiplication. We demonstrate the promise of this method for applications to higher multiplicity/loop correlation functions.

Stellar tidal streams provide an opportunity to study the motion and structure of the disrupting galaxy as well as the gravitational potential of its host. Streams around the Milky Way are especially promising as phase space positions of individual stars will he measured by ongoing or upcoming surveys. Nevertheless, it remains a challenge to accurately assess distances to stars farther than 10 kpc from the Sun, where we have the poorest knowledge of the Galaxy's mass distribution. To address this, we present observations of 32 candidate RR Lyrae stars in the Orphan tidal stream taken as part of the Spitzer Merger History and Shape of the Galactic Halo (SMHASH) program. The extremely tight correlation between the periods, luminosities, and metallicities of RR Lyrae variable stars in the Spitzer IRAC 3.6 mu m band allows the determination of precise distances to individual stars; the median statistical relative distance uncertainty to each RR Lyrae star is 2.5 per cent. By fitting orbits in an example potential, we obtain an upper limit on the mass of the Milky Way interior to 60 kpc of 5.6(-1.1)(+1.2) x 10(11) M-circle dot, bringing estimates based on the Orphan Stream in line with those using other tracers. The SMHASH data also resolve the stream in line-of-sight depth, allowing a new perspective on the internal structure of the disrupted dwarf galaxy. Comparing with N body models, we find that the progenitor had an initial dark halo mass of approximately 3,2 x 10(9) M-circle dot, placing the Orphan Stream's progenitor amongst the classical dwarf spheroidals.

We present nebular-phase spectra of the Type Ia supernova (SN Ia) 2016brx, a member of the 1991bg-like subclass that lies at the faint end of the SN Ia luminosity function. Nebular spectra are available for only three other 1991bg-like SNe, and their Co line centres are all within less than or similar to 500 km s(-1) of each other. In contrast, the nebular Co line centre of SN 2016brx is blue-shifted by >1500 km s(-1) compared to them and by approximate to 1200 km s(-1) compared to the rest frame. This is a significant shift relative to the narrow nebular line velocity dispersion of less than or similar to 2000 km s(-1) of these SNe. The large range of nebular line shifts implies that the Ni-56 in the ejecta of SN 1991bg-like events is off-centre by similar to 1000 km s(-1) rather than universally centrally confined as previously suggested. With the addition of SN 2016brx, the Co nebular line shapes of 1991bg-like objects appear to connect with the brighter SNe Ia that show double-peaked profiles, hinting at a continuous distribution of line profiles among SNe la. One class of models to produce both off-centre and bimodal Ni-56 distributions is collisions of white dwarfs with unequal and equal masses.

We present photometry of 30 Galactic RR Lyrae variables taken with HST WFC3/IR for the Carnegie-Chicago Hubble Program. These measurements form the base of the distance-ladder measurements that comprise a pure Population II base to a measurement of H-o at an accuracy of 3%. These data are taken with the same instrument and filter (F160W) as our observations of RR Lyrae stars in external galaxies so as to minimize sources of systematic error in our calibration of the extragalactic distance scale. We calculate mean magnitudes based on one to three measurements for each RR Lyrae star using star-by-star templates generated from densely time-sampled data at optical and midinfrared wavelengths. We use four RR Lyrae stars from our sample with well-measured HST parallaxes to determine a zero-point. This zero-point will soon be improved with the large number of precise parallaxes to be provided by Gaia. We also provide preliminary calibration with the TGAS and Gaia DR2 data, and all three zero points are in agreement, to within their uncertainties.

We describe test observations made with a customized 640 x 512 pixel indium gallium arsenide (InGaAs) prototype astronomical camera on the 2.5 m DuPont telescope. This is the first test of InGaAs as a cost-effective alternative to HgCdTe for research-grade astronomical observations. The camera exhibits a background of 113 e(-1) s(-1)/pixel (dark + thermal) at operating sensor temperature T = -40 degrees C, maintained by a simple thermoelectric cooler. The optomechanical structure floats at ambient temperature with no cold stop, unlike most IR instruments which must be cooled to mitigate thermal backgrounds. Measurements of the night sky using a reimager scaled at 0.'' 4/pixel show that the sky flux in Y is comparable to the dark current. At J the sky exceeds dark current by a factor of four, dominating the noise budget. The read noise (similar to 43 e(-)) falls below sky + dark noise for exposures of t > 7 s in Y and 3.5 s in J. We observed several representative science targets, including two supernovae, a z = 6.3 quasar, two local galaxies monitored for IR transients, and a galaxy cluster at z = 0.87. We observe a partial transit of the hot Jupiter HATS-34b, demonstrating the photometric stability to detect a 1.2% transit. A tiling of larger-format sensors would produce an IR survey instrument with significant cost savings relative to HgCdTe-based cameras, if one is willing to forego the K band. Such a camera would be sensitive for a week or more to isotropic emission from r-process kilonova ejecta similar to that observed in GW170817, over the full 190 Mpc horizon of Advanced LIGO.

We test and improve the numerical schemes in our smoothed particle hydrodynamics (SPH) code for cosmological simulations, including the pressure-entropy formulation (PESPH), a time-dependent artificial viscosity, a refined time-step criterion, and metal-line cooling that accounts for photoionization in the presence of a recently refined Haardt & Madau model of the ionizing background. The PESPH algorithm effectively removes the artificial surface tension present in the traditional SPH formulation, and in our test simulations, it produces better qualitative agreement with mesh-code results for Kelvin-Helmholtz instability and cold cloud disruption. Using a set of cosmological simulations, we examine many of the quantities we have studied in previous work. Results for galaxy stellar and Hi mass functions, star formation histories, galaxy scaling relations, and statistics of the Ly alpha forest are robust to the changes in numerics and microphysics. As in our previous simulations, cold gas accretion dominates the growth of high-redshift galaxies and of low-mass galaxies at low redshift, and recycling of winds dominates the growth of massive galaxies at low redshift. However, the PESPH simulation removes spurious cold clumps seen in our earlier simulations, and the accretion rate of hot gas increases by up to an order of magnitude at some redshifts. The new numerical model also influences the distribution of metals among gas phases, leading to considerable differences in the statistics of some metal absorption lines, most notably Ne VIII.

We report the detection of a hot Jupiter (M-p = 1.75(-0.17)(+0.14) M-J, R-p = 1.38 +/- 0.04R(J)) orbiting a middle-aged star (log g = 4.152(-0.043)(+0.030)) in the Transiting Exoplanet Survey Satellite (TESS) southern continuous viewing zone (beta = -79 degrees.59). We confirm the planetary nature of the candidate TOI-150.01 using radial velocity observations from the APOGEE-2 South spectrograph and the Carnegie Planet Finder Spectrograph, ground-based photometric observations from the robotic Three-hundred MilliMeter Telescope at Las Campanas Observatory, and Gaia distance estimates. Large-scale spectroscopic surveys, such as APOGEE/APOGEE-2, now have sufficient radial velocity precision to directly confirm the signature of giant exoplanets, making such data sets valuable tools in the TESS era. Continual monitoring of TOI-150 by TESS can reveal additional planets and subsequent observations can provide insights into planetary system architectures involving a hot Jupiter around a star about halfway through its main-sequence life.

As part of the 100IAS survey, a program aimed to obtain nebular-phase spectra for a volume-limited and homogeneous sample of Type Ia supernovae (SNe Ia), we observed ASASSN-18tb (SN 2018fhw) at 139 d past maximum light. ASASSN-18tb was a fast-declining, sub-luminous event that fits well within the observed photometric and spectroscopic distributions of the SN Ia population. We detect a prominent H alpha emission line (L-H alpha = 2.2 +/- 0.2 x 10(38) ergs s(-1)) with FWHM approximate to 1100 km s(-1) in the nebular-phase spectrum of this SN Ia. High-luminosity H alpha emission (L-H alpha greater than or similar to 10(40) ergs s(-1)) has previously been discovered in a rare class of SNe Ia-like objects showing circum-stellar medium (CSM) interactions (SNe Ia-CSM). They predominantly belong to overluminous (M-max <-19 mag in optical) 1991T-like SNe Ia and are exclusively found in star-forming galaxies. By contrast, ASASSN-18tb is a sub-luminous SN Ia (M-B,M-max similar to-17.7mag) found in an early-type galaxy dominated by old stellar populations. We discuss possible origins for the observed hydrogen. Of the 75 SNe Ia for which we have so far obtained nebular spectra in 100IAS, no other SN shows a similar to 1000 km s(-1) H alpha emission line with comparable line luminosity as ASASSN-18tb, emphasizing the rarity of such emission in the nebular phase. Based on preliminary results from our survey, the rate for ASASSN-18tb-like nebular H alpha emission could be as high as similar to 10 per cent among sub-luminous SNe Ia.