During the summer of 2013, a 4-month spectroscopic campaign took place to observe the variabilities in three Wolf-Rayet stars. The spectroscopic data have been analyzed for WR 134 (WN6b), to better ...understand its behaviour and long-term periodicity, which we interpret as arising from corotating interaction regions (CIRs) in the wind. By analyzing the variability of the He II \(\lambda\)5411 emission line, the previously identified period was refined to P = 2.255 \(\pm\) 0.008 (s.d.) days. The coherency time of the variability, which we associate with the lifetime of the CIRs in the wind, was deduced to be 40 \(\pm\) 6 days, or \(\sim\) 18 cycles, by cross-correlating the variability patterns as a function of time. When comparing the phased observational grayscale difference images with theoretical grayscales previously calculated from models including CIRs in an optically thin stellar wind, we find that two CIRs were likely present. A separation in longitude of \(\Delta \phi \simeq\) 90\(^{\circ}\) was determined between the two CIRs and we suggest that the different maximum velocities that they reach indicate that they emerge from different latitudes. We have also been able to detect observational signatures of the CIRs in other spectral lines (C IV \(\lambda\lambda\)5802,5812 and He I \(\lambda\)5876). Furthermore, a DAC was found to be present simultaneously with the CIR signatures detected in the He I \(\lambda\)5876 emission line which is consistent with the proposed geometry of the large-scale structures in the wind. Small-scale structures also show a presence in the wind, simultaneously with the larger scale structures, showing that they do in fact co-exist.
We report on the discovery of a fourth component in the HD 221356 star system, previously known to be formed by an F8V, slightly metal-poor primary (Fe/H=-0.26), and a distant M8V+L3V pair. In our ...ongoing common proper motion search based on VISTA Hemisphere Survey (VHS) and 2MASS catalogues, we have detected a faint (J=13.76+/-0.04 mag) co-moving companion of the F8 star located at angular separation of 12.13+/-0.18 arcsec (position angle of 221.8+/-1.7), corresponding to a projected distance of ~312 AU at 26 pc. Near-infrared spectroscopy of the new companion, covering the 1.5-2.4 micron wavelength range with a resolving power of R~600, indicates an L1+/-1 spectral type. Using evolutionary models the mass of the new companion is estimated at ~0.08 solar masses, which places the object close to the stellar-substellar borderline. This multiple system provides an interesting example of objects with masses slightly above and below the hydrogen burning mass limit. The low mass companions of HD 221356 have slightly bluer colours than field dwarfs with similar spectral type, which is likely a consequence of the sub-solar metallicity of the system.
A method is defined for identifying late T and Y dwarfs in WISE down to low values of signal-to-noise. This requires a WISE detection only in the W2-band and uses the statistical properties of the ...WISE multi-frame measurements and profile fit photometry to reject contamination resulting from non-point-like objects, variables and moving sources. To trace our desired parameter space we use a control sample of isolated non-moving non-variable point sources from the SDSS, and identify a sample of 158 WISE W2-only candidates down to a signal-to-noise limit of 8. For signal-to-noise ranges >10 and 8-10 respectively, ~45% and ~90% of our sample fall outside the selection criteria published by the WISE team (Kirkpatrick et al. 2012), due mainly to the type of constraints placed on the number of individual W2 detections. We present follow-up of eight candidates and identify WISE 0013+0634 and WISE 0833+0052, T8 and T9 dwarfs with high proper motion (~1.3 and ~1.8 arcsec/yr). Both objects show a mid-infrared/near-infrared excess of ~1-1.5 magnitudes, and are K-band suppressed. Distance estimates lead to space motion constraints that suggest halo (or at least thick disk) kinematics. We then assess the reduced proper motion diagram of WISE ultracool dwarfs, which suggests that late T and Y dwarfs may have a higher thick-disk/halo population fraction than earlier objects.
A simple method is developed for aligning the laterally difluorinated high birefringence liquid crystal (LC) compounds and mixtures in a homeotropic cell. Adding a few percent positive dielectric ...anisotropic or nonpolar LC material not only enhances the contrast ratio but also improves the overall figure-of-merit. Several negative LC compounds with a wide variation of birefringence are used to investigate this phenomenon. Molecular modeling and experimentation are demonstrated to support this concept.
UV stable, high birefringence and low viscosity nematic liquid crystal mixtures were developed and their properties evaluated. Our new mixtures exhibit similar birefringence but ∼3.5X lower ...visco‐elastic coefficient than Merck E44. In the mean time, our new mixtures show better UV stability than those cyano‐biphenyls based commercial mixtures. To make a performance of new material more visible a high birefringence and relatively low viscosity liquid crystal mixture was developed for this experiment in conjunction with the voltage overdrive and undershoot technique. We demonstrated a liquid crystal light switch with response time ∼50 μs at room temperature and λ= 633 nm Potential application for sub‐millisecond laser beam steering is emphasized.
Mixtures of 4-cyano-4′-hydroxyazobenzene 4-n-octyloxybenzoate (8OBCAB) - constant compound and 4′-X-phenyl 4-n-decylbenzoate or 4′-X-phenyl 4-n-decyloxybenzoate (10.X, 10.O.X) - the variable compound ...in which X refers to the terminal group CN, NO
2
, NCS, COCH
3
, Cl or F, were studied by thermomicroscopic and X-ray methods. The influence of the terminal groups on the kind of phases and their miscibility was observed. The enhancement of the smectic A
d
phase together with the appearance of the nematic gap between A
d
and A
1
smectic phases and re-entrant nematic phase were observed in mixtures with high polar compounds (-CN, -NO
2
). Complete miscibility together with an increase of smectic A phase persistence were observed in mixtures with medium polar compounds (-NCS, -COCH
3
). Additive miscibility was observed in mixtures with low polar compounds (-Cl, F).
