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We present a kinematic study of the nuclear stellar disk in M31 at infrared wavelengths using high spatial resolution integral field spectroscopy. The spatial resolution achieved, FWHM = 0.″12 (0.45 pc at the distance of M31), has only previously been equaled in spectroscopic studies by space-based long-slit observations. Using adaptive-optics-corrected integral field spectroscopy from the OSIRIS instrument at the W. M. Keck Observatory, we map the line-of-sight kinematics over the entire old stellar eccentric disk orbiting the supermassive black hole (SMBH) at a distance of r < 4 pc. The peak velocity dispersion is 381 ± 55 km s−1, offset by 0.″13 ± 0.″03 from the SMBH, consistent with previous high-resolution long-slit observations. There is a lack of near-infrared (NIR) emission at the position of the SMBH and young nuclear cluster, suggesting a spatial separation between the young and old stellar populations within the nucleus. We compare the observed kinematics with dynamical models from Peiris & Tremaine. The best-fit disk orientation to the NIR flux is [θl, θi, θa] = [−33° ± 4°, 44° ± 2°, −15° ± 15°], which is tilted with respect to both the larger-scale galactic disk and the best-fit orientation derived from optical observations. The precession rate of the old disk is ΩP = 0.0 ± 3.9 km s−1 pc−1, lower than the majority of previous observations. This slow precession rate suggests that stellar winds from the disk will collide and shock, driving rapid gas inflows and fueling an episodic central starburst as suggested in Chang et al. [ABSTRACT FROM AUTHOR]

While dozens of stellar-mass black holes (BHs) have been discovered in binary systems, isolated BHs have eluded detection. Their presence can be inferred when they lens light from a background star. We attempt to detect the astrometric lensing signatures of three photometrically identified microlensing events, OGLE-2011-BLG-0022, OGLE-2011-BLG-0125, and OGLE-2012-BLG-0169 (OB110022, OB110125, and OB120169), located toward the Galactic Bulge. These events were selected because of their long durations, which statistically favors more massive lenses. Astrometric measurements were made over one to two years using laser-guided adaptive optics observations from the W. M. Keck Observatory. Lens model parameters were first constrained by the photometric light curves. The OB120169 light curve is well fit by a single-lens model, while both OB110022 and OB110125 light curves favor binary lens models. Using the photometric fits as prior information, no significant astrometric lensing signal was detected and all targets were consistent with linear motion. The significant lack of astrometric signal constrains the lens mass of OB110022 to 0.05–1.79 M⊙ in a 99.7% confidence interval, which disfavors a BH lens. Fits to OB110125 yielded a reduced Einstein crossing time and insufficient observations during the peak, so no mass limits were obtained. Two degenerate solutions exist for OB120169, which have a lens mass between 0.2–38.8 M⊙ and 0.4–39.8 M⊙ for a 99.7% confidence interval. Follow-up observations of OB120169 will further constrain the lens mass. Based on our experience, we use simulations to design optimal astrometric observing strategies and show that with more typical observing conditions the detection of BHs is feasible. [ABSTRACT FROM AUTHOR]

We present a new geometric distortion model for the narrow-field mode of the near-infrared camera (NIRC2) fed by the adaptive optics system on the W. M. Keck II telescope. The adaptive optics system and NIRC2 camera were realigned on 2015 April 13. Observations of the crowded globular cluster, M53, were obtained before and after the realignment to characterize the geometric field distortion. The distorted NIRC2 positions of M53 stars were compared with precise astrometry of this cluster from Hubble Space Telescope observations. The resulting distortion map constructed just before the realignment is consistent with the previous solution derived using data from 2007 to 2009, indicating that the distortion has been stable to ∼0.5 mas. The distortion map changed significantly after a realignment of 4.5 mas (75%) rms, and the new distortion model for post-realignment observations have a total accuracy of ∼1.1 mas. [ABSTRACT FROM AUTHOR]

The structure of the adsorbed proteinlayer at the oil/water interfaceis essential to the understanding of the role of proteins in emulsionstabilization, and it is important to glean the mechanistic eventsof protein adsorption at such buried interfaces. This article reportson a novel experimental methodology for probing protein adsorptionat the buried oil/water interface. Neutron reflectivity was used witha carefully selected set of isotopic contrasts to study the adsorptionof bovine serum albumin (BSA) at the hexadecane/water interface, andthe results were compared to those for the air/water interface. Theadsorption isotherm was determined at the isoelectric point, and theresults showed that a higher degree of adsorption could be achievedat the more hydrophobic interface. The adsorbed BSA molecules formeda monolayer on the aqueous side of the interface. The molecules inthis layer were partially denatured by the presence of oil, and oncereleased from the spatial constraint by the globular framework theywere free to establish more favorable interactions with the hydrophobicmedium. Thus, a loose layer extending toward the oil phase was clearlyobserved, resulting in an overall broader interface. By analogy tothe air/water interface, as the concentration of BSA increased to1.0 mg mL–1a secondary layer extending toward theaqueous phase was observed, possibly resulting from the steric repulsionupon the saturation of the primary monolayer. Results clearly indicatea more compact arrangement of molecules at the oil/water interface:this must be caused by the loss of the globular structure as a consequenceof the denaturing action of the hexadecane. [ABSTRACT FROM AUTHOR]

We have characterized three diblock copolymers bearing zwitterionic phosphorylcholine and weak tertiary amine groups, namely, poly[((2-(methacryloyloxy)ethyl)phosphorylcholine) 30- block-(2-(dimethylamino)ethyl methacrylate) 60] (denoted as MPC 30−DMA 60, Mn= 18 000), poly[((2-(methacryloyloxy)ethyl)phosphorylcholine) 30- block-(2-(diethylamino)ethyl methacrylate) 60) (denoted as MPC 30−DEA 60, Mn= 20 000), and poly[((2-(methacryloyloxy)ethyl)phosphorylcholine) 30- block-(2-(diisopropylamino)ethyl methacrylate) 60) (denoted as MPC 30−DPA 60, Mn= 21 000), by studying their surface tension and solution aggregation through a combined approach of surface tension measurement, dynamic light scattering, and small-angle neutron scattering. Our results show that larger tertiary amine substituents lead to an increasing tendency to form micellar aggregates, which is consistent with the increasing copolymer hydrophobicity. Thus, MPC 30−DMA 60did not aggregate under the experimental conditions studied. The free chains exist in the form of thin cylinders, whose length decreases with copolymer concentration and solution temperature but increases with solution pH. The diameters of the MPC 30−DMA 60cylinders remained almost constant at around 30 Å under all the conditions studied. At the lower copolymer concentration of 0.5 wt %, the cylindrical lengths correspond to the persistence length of the copolymer backbone and are close to its full length, indicating a rather high rigidity. Further data analysis showed that, at the two higher concentrations of 2 and 4 wt %, the phosphorylcholine and amine blocks associate, inducing bending of the copolymer backbone. One backbone kink was required to satisfy all the constraints, including the dry volume of the copolymer. MPC 30−DEA 60showed a similar trend of pH- and concentration-dependent conformational responses for the free copolymer, but in addition micellar aggregation occurred at pH 9. In contrast, MPC 30−DPA 60exhibited significantly reduced solubility associated with strong aggregation, which is consistent with it being the most hydrophobic copolymer in the series. [ABSTRACT FROM AUTHOR]

In various fields of physics and astronomy, access to experimental facilities or to telescopes is becoming more and more competitive and limited. It therefore becomes important to optimize the type of measurements and their scheduling to reach a given scientific objective and to increase the chances of success of a scientific project. In this communication, extending the work of Ford and of Loredo et al., we present an efficient adaptive scheduling tool aimed at prioritizing measurements in order to reach a scientific goal. The algorithm, based on the Fisher matrix, can be applied to a wide class of measurements. We present this algorithm in detail and discuss some practicalities such as systematic errors or measurement losses due to contingencies (such as weather, experimental failure, ...). As an illustration, we consider measurements of the short-period star S0-2 in our Galactic Center (GC). We show that the radial velocity measurements at the two turning points of the radial velocity curve are more powerful for detecting the gravitational redshift than measurements at the maximal relativistic signal. We also explicitly present the methodology that was used to plan measurements in order to detect the relativistic redshift considering systematics and possible measurement losses. For the future, we identify the astrometric turning points to be highly sensitive to the relativistic advance of the periastron. Finally, we also identify measurements particularly sensitive to the distance to our GC: the radial velocities around periastron and the astrometric measurements just before closest approach and at the maximal R.A. astrometric turning point. [ABSTRACT FROM AUTHOR]

We present new adaptive optics (AO) imaging and spectroscopic measurements of Galactic center source G1 from W. M. Keck Observatory. Our goal is to understand its nature and relationship to G2, which is the first example of a spatially resolved object interacting with a supermassive black hole (SMBH). Both objects have been monitored with AO for the past decade (2003–2014) and are comparatively close to the black hole (amin ∼ 200–300 au) on very eccentric orbits (eG1 ∼ 0.99; eG2 ∼ 0.96). While G2 has been tracked before and during periapsis passage (T0 ∼ 2014.2), G1 has been followed since soon after emerging from periapsis (T0 ∼ 2001.3). Our observations of G1 double the previously reported observational time baseline, which improves its orbital parameter determinations. G1's orbital trajectory appears to be in the same plane as that of G2 but with a significantly different argument of periapsis (Δω = 21° ± 4°). This suggests that G1 is an independent object and not part of a gas stream containing G2, as has been proposed. Furthermore, we show for the first time that (1) G1 is extended in the epochs closest to periapsis along the direction of orbital motion, and (2) it becomes significantly smaller over time (450 au in 2004 to less than 170 au in 2009). Based on these observations, G1 appears to be the second example of an object tidally interacting with an SMBH. G1's existence 14 yr after periapsis, along with its compactness in epochs further from the time of periapsis, suggest that this source is stellar in nature. [ABSTRACT FROM AUTHOR]

We present new, more precise measurements of the mass and distance of our Galaxy’s central supermassive black hole, Sgr A*. These results stem from a new analysis that more than doubles the time baseline for astrometry of faint stars orbiting Sgr A*, combining 2 decades of speckle imaging and adaptive optics data. Specifically, we improve our analysis of the speckle images by using information about a star’s orbit from the deep adaptive optics data (2005–2013) to inform the search for the star in the speckle years (1995–2005). When this new analysis technique is combined with the first complete re-reduction of Keck Galactic Center speckle images using speckle holography, we are able to track the short-period star S0-38 (K-band magnitude = 17, orbital period = 19 yr) through the speckle years. We use the kinematic measurements from speckle holography and adaptive optics to estimate the orbits of S0-38 and S0-2 and thereby improve our constraints of the mass (Mbh) and distance (Ro) of Sgr A*: Mbh = (4.02 ± 0.16 ± 0.04) × 106M⊙ and 7.86 ± 0.14 ± 0.04 kpc. The uncertainties in Mbh and Ro as determined by the combined orbital fit of S0-2 and S0-38 are improved by a factor of 2 and 2.5, respectively, compared to an orbital fit of S0-2 alone and a factor of ∼2.5 compared to previous results from stellar orbits. This analysis also limits the extended dark mass within 0.01 pc to less than 0.13 × 106M⊙ at 99.7% confidence, a factor of 3 lower compared to prior work. [ABSTRACT FROM AUTHOR]