12,032 research outputs found
Alessi 95 and the short period Cepheid SU Cassiopeiae
The parameters for the newly-discovered open cluster Alessi 95 are
established on the basis of available photometric and spectroscopic data, in
conjunction with new observations. Colour excesses for
spectroscopically-observed B and A-type stars near SU Cas follow a reddening
relation described by E(U-B)/E(B-V)=0.83+0.02*E(B-V), implying a value of
R=Av/E(B-V)~2.8 for the associated dust. Alessi 95 has a mean reddening of
E(B-V)_(B0)=0.35+-0.02 s.e., an intrinsic distance modulus of Vo-Mv=8.16+-0.04
s.e. (+-0.21 s.d.), d=429+-8 pc, and an estimated age of 10^8.2 yr from ZAMS
fitting of available UBV, CCD BV, NOMAD, and 2MASS JHKs observations of cluster
stars. SU Cas is a likely cluster member, with an inferred space reddening of
E(B-V)=0.33+-0.02 and a luminosity of =-3.15+-0.07 s.e., consistent with
overtone pulsation (P_FM=2.75 d), as also implied by the Cepheid's light curve
parameters, rate of period increase, and Hipparcos parallaxes for cluster
stars. There is excellent agreement of the distance estimates for SU Cas
inferred from cluster ZAMS fitting, its pulsation parallax derived from the
infrared surface brightness technique, and Hipparcos parallaxes, which all
agree to within a few percent.Comment: Accepted for Publication (MNRAS
The period change of the Cepheid Polaris suggests enhanced mass loss
Polaris is one of the most observed stars in the night sky, with recorded
observations spanning more than 200 years. From these observations, one can
study the real-time evolution of Polaris via the secular rate of change of the
pulsation period. However, the measurements of the rate of period change do not
agree with predictions from state-of-the-art stellar evolution models. We show
that this may imply that Polaris is currently losing mass at a rate of yr based on the difference between modeled and
observed rates of period change, consistent with pulsation-enhanced Cepheid
mass loss. A relation between the rate of period change and mass loss has
important implications for understanding stellar evolution and pulsation, and
provides insight into the current Cepheid mass discrepancy.Comment: 5 pages, 4 figures, compiled using emulateapj, Accepted for
publication in ApJ Letters. Fixed correction in titl
Double Rotating Wall Compression of Positron Clouds and Towards Resistive Cooling
Low energy positron clouds from a buer gas trap have been characterised and compressed by a novel double rotating wall (RW) electric field. A theoretical and experimental study comparing compression due to dipolar single and double RW electric fields is presented, with details of a custom-built function generator capable of operating on two sets of four, six, and eight-segment electrodes. The installation of a cylindrical Penning trap with two sets of six-segment RW elec-trodes has allowed the implementation of a double RW, which provides a better approximation to the electric potential in the model for independent charged par-ticle compression. A reduction in particle heating has been observed with the double RW, whilst obtaining at least equivalent compression as the single RW, which may in future allow a reduction in the minimum attainable cloud width.Without the use of RW electric fields, optimisations to positron ejection and recapture techniques led to positron clouds being held in a deep, harmonic poten-tial well for over 100 s, enabling time to study RW electric fields and to perform resistive cooling experiments
Discovery of the Host Cluster for the Fundamental Cepheid Calibrator Zeta Gem
New and existing CORAVEL, UBVJHKs, HST, HIP/Tycho, ARO, KPNO, and DAO
observations imply that the fundamental Cepheid calibrator Zeta Gem is a
cluster member. The following parameters were inferred for Zeta Gem from
cluster membership and are tied to new spectral classifications (DAO)
established for 26 nearby stars (e.g., HD53588/B7.5IV, HD54692/B9.5IV):
E(B-V)=0.02+-0.02, log t=7.85+-0.15, and d=355+-15 pc. The mean distance to
Zeta Gem from cluster membership and six recent estimates (e.g., IRSB) is
d=363+-9(se)+-26(sd) pc. The results presented here support the color-excess
and HST parallax derived for the Cepheid by Benedict et al. (2007). Forthcoming
precise proper motions (DASCH) and Chandra/XMM-Newton observations of the
broader field may be employed to identify cluster members, bolster the
cluster's existence, and provide stronger constraints on the Cepheid's
fundamental parameters.Comment: To appear in ApJ Letter
Buying Your First Horse
This publications gives information about evaluating a horse for purchase, age and experience of new owner, breed and sex of horse, intended use, care and housing, cost of ownership, locating the right horse, and trying it out
Conformal GaP layers on Si wire arrays for solar energy applications
We report conformal, epitaxial growth of GaP layers on arrays of Si microwires. Silicon wires grown using chlorosilane chemical vapor deposition were coated with GaP grown by metal-organic chemical vapor deposition. The crystalline quality of conformal, epitaxial GaP/Si wire arrays was assessed by transmission electron microscopy and x-ray diffraction. Hall measurements and photoluminescence show p- and n-type doping with high electron mobility and bright optical emission. GaP pn homojunction diodes on planar reference samples show photovoltaic response with an open circuit voltage of 660 mV
- …