The Distance To The Hyades Cluster Based On Hubble Space Telescope Fine Guidance Sensor Parallaxes

Trigonometric parallax observations made with the Hubble Space Telescope (HST) Fine Guidance Sensor (FGS) 3 of seven Hyades members in six fields of view have been analyzed along with their proper motions to determine the distance to the cluster. Knowledge of the convergent point and mean proper motion of the Hyades is critical to the derivation of the distance to the center of the cluster. Depending on the choice of the proper-motion system, the derived cluster center distance varies by 9%. Adopting a reference distance of 46.1 pc or m - M = 3.32, which is derived from the ground-based parallaxes in the General Catalogue of Trigonometric Stellar Parallaxes (1995 edition), the FK5/PPM proper-motion system yields a distance 4% larger, while the Hanson system yields a distance 2% smaller. The HST FGS parallaxes reported here yield either a 14% or 5% larger distance, depending on the choice of the proper-motion system. Orbital parallaxes (Torres et al.) yield an average distance 4% larger than the reference distance. The variation in the distance derived from the HST data illustrates the importance of the proper-motion system and the individual proper motions to the derivation of the distance to the Hyades center; therefore, a full utilization of the HST FGS parallaxes awaits the establishment of an accurate and consistent proper-motion system.NASA HST GTO, HF-1042.01-93A, HF-1046.01-93A, NAS526555Astronom

Astrometry with Hubble Space Telescope: A Parallax of the Fundamental Distance Calibrator RR Lyrae

We present an absolute parallax and relative proper motion for the fundamental distance scale calibrator, RR Lyr. We obtain these with astrometric data from FGS 3, a white-light interferometer on HST. We find $\pi_{abs} = 3.82 \pm 0.2$ mas. Spectral classifications and VRIJHKT$_2$M and DDO51 photometry of the astrometric reference frame surrounding RR Lyr indicate that field extinction is low along this line of sight. We estimate =0.07\pm0.03 for these reference stars. The extinction suffered by RR Lyr becomes one of the dominant contributors to the uncertainty in its absolute magnitude. Adopting the average field absorption, =0.07 \pm 0.03, we obtain M_V^{RR} = 0.61 ^{-0.11}_{+0.10}. This provides a distance modulus for the LMC, m-M = 18.38 - 18.53^{-0.11}_{+0.10} with the average extinction-corrected magnitude of RR Lyr variables in the LMC, , remaining a significant uncertainty. We compare this result to more than 80 other determinations of the distance modulus of the LMC.Comment: Several typos corrected. To appear in The Astronomical Journal, January 200

Search for TeV Gamma-Rays from Shell-Type Supernova Remnants

If cosmic rays with energies <100 TeV originate in the galaxy and are accelerated in shock waves in shell-type supernova remnants (SNRs), gamma-rays will be produced as the result of proton and electron interactions with the local interstellar medium, and by inverse Compton emission from electrons scattering soft photon fields. We report on observations of two supernova remnants with the Whipple Observatory's 10 m gamma-ray telescope. No significant detections have been made and upper limits on the >500 GeV flux are reported. Non-thermal X-ray emission detected from one of these remnants (Cassiopeia A) has been interpreted as synchrotron emission from electrons in the ambient magnetic fields. Gamma-ray emission detected from the Monoceros/Rosette Nebula region has been interpreted as evidence of cosmic-ray acceleration. We interpret our results in the context of these observations.Comment: 4 pages, 2 figures, to appear in the proceedings of 26th International Cosmic Ray Conference (Salt Lake City, 1999

Bibliometric Analysis of Female Authorship Trends and Collaboration Dynamics Over JBMR's 30-Year History

In academia, authorship is considered a currency and is important for career advancement. As the Journal of Bone and Mineral Research (JBMR) is the highest-ranked journal in the field of bone, muscle, and mineral metabolism and is the official publication of the American Society for Bone and Mineral Research, we sought to examine authorship changes over JBMR's 30-year history. Two bibliometric methods were used to collect the data. The “decade method” included all published manuscripts throughout 1 year in each decade over the past 30 years starting with the inaugural year, yielding 746 manuscripts for analysis. The “random method” examined 10% of published manuscripts from each of the 30 years, yielding 652 manuscripts for analysis. Using both methods, the average number of authors per manuscript, numerical location of the corresponding author, number of collaborating institutions, number of collaborating countries, number of printed manuscript pages, and the number of times each manuscript was cited all significantly increased between 1986 and 2015 (p < 10−4). Using the decade method, there was a significant increase in the percentage of female first authors over time from 35.8% in 1986 to 47.7% in 2015 (p = 0.02), and this trend was confirmed using the random method. The highest percentage of female first authors in 2015 was in Europe (60.0%), and Europe also had the most dramatic increase in female first authors over time (more than double in 2015 compared with 1986). Likewise, the overall number of female corresponding authors significantly increased during the past 30 years. With the increasing demands of publishing in academic medicine, understanding changes in publishing characteristics over time and by geographical region is important. These findings highlight JBMR's authorship trends over the past 30 years and demonstrate those countries having the most changes and where challenges still exist

Active spacecraft potential control for Cluster ? implementation and first results

International audienceElectrostatic charging of a spacecraft modifies the distribution of electrons and ions before the particles enter the sensors mounted on the spacecraft body. The floating potential of magnetospheric satellites in sunlight very often reaches several tens of volts, making measurements of the cold (several eV) component of the ambient ions impossible. The plasma electron data become contaminated by large fluxes of photoelectrons attracted back into the sensors. The Cluster spacecraft are equipped with emitters of the liquid metal ion source type, producing indium ions at 5 to 9 keV energy at currents of some tens of microampere. This current shifts the equilibrium potential of the spacecraft to moderately positive values. The design and principles of the operation of the instrument for active spacecraft potential control (ASPOC) are presented in detail. Experience with spacecraft potential control from the commissioning phase and the first two months of the operational phase are now available. The instrument is operated with constant ion current for most of the time, but tests have been carried out with varying currents and a "feedback" mode with the instrument EFW, which measures the spacecraft potential . That has been reduced to values according to expectations. In addition, the low energy electron measurements show substantially reduced fluxes of photoelectrons as expected. The flux decrease in photoelectrons returning to the spacecraft, however, occurs at the expense of an enlarged sheath around the spacecraft which causes problems for boom-mounted probes

THE SPIRAL WAVE INSTABILITY INDUCED BY A GIANT PLANET. I. PARTICLE STIRRING IN THE INNER REGIONS OF PROTOPLANETARY DISKS

We have recently shown that spiral density waves propagating in accretion disks can undergo a parametric instability by resonantly coupling with and transferring energy into pairs of inertial waves (or inertial-gravity waves when buoyancy is important). In this paper, we perform inviscid three-dimensional global hydrodynamic simulations to examine the growth and consequence of this instability operating on the spiral waves driven by a Jupiter-mass planet in a protoplanetary disk. We find that the spiral waves are destabilized via the spiral wave instability (SWI), generating hydrodynamic turbulence and sustained radially-alternating vertical flows that appear to be associated with long wavelength inertial modes. In the interval $0.3~R_p \leq R \leq 0.7~R_p$, where $R_p$ denotes the semi-major axis of the planetary orbit (assumed to be 5~au), the estimated vertical diffusion rate associated with the turbulence is characterized by $\alpha_{\rm diff} \sim (0.2-1.2) \times 10^{-2}$. For the disk model considered here, the diffusion rate is such that particles with sizes up to several centimeters are vertically mixed within the first pressure scale height. This suggests that the instability of spiral waves launched by a giant planet can significantly disperse solid particles and trace chemical species from the midplane. In planet formation models where the continuous local production of chondrules/pebbles occurs over Myr time scales to provide a feedstock for pebble accretion onto these bodies, this stirring of solid particles may add a time constraint: planetary embryos and large asteroids have to form before a gas giant forms in the outer disk, otherwise the SWI will significantly decrease the chondrule/pebble accretion efficiency.Comment: Accepted for publication in the The Astrophysical Journal, 19 pages, 12 figures, 1 tabl

Zn Diffusion and α-Fe(Zn) Layer Growth During Annealing of Zn-Coated B Steel

Direct hot press forming of Zn-coated 22MnB5 steels is impeded by micro-cracks that occur in the substrate due to the presence of Zn during the forming process. A study was therefore undertaken to quantify concentration of Zn across the α-Fe(Zn) coating and on grain boundaries in the α-Fe(Zn) layer and the underlying γ-Fe(Zn) substrate after isothermal annealing of Zn-coated 22MnB5 at 1173 K (900 °C) and to link the Zn distribution to the amount and type of micro-cracks observed in deformed samples. Finite difference model was developed to describe Zn diffusion and the growth of the α-Fe(Zn) layer. The penetration of Zn into the γ-Fe(Zn) substrate after 600 seconds annealing at 1173 K (900 °C) through bulk diffusion is estimated to be 3 μm, and the diffusion depth of Zn on the γ-Fe(Zn) grain boundaries is estimated to be 6 μm, which is significantly shorter than the maximum length (15 to 50 μm) of the micro-cracks formed in the severely stressed conditions, indicating that the Zn diffusion into the γ-Fe(Zn) from the α-Fe(Zn) during annealing is not correlated to the depth of micro-cracks. On the other hand, the maximum amount of Zn present in α-Fe(Zn) layer decreases with annealing time as the layer grows and Zn oxidizes, and the amount of Zn-enriched areas inside the α-Fe(Zn) layer is reduced leading to reduced length of cracking. Solid-Metal-Induced Embrittlement mechanism is proposed to explain the benefit of extended annealing on reduced depth of micro-crack penetration into the γ-Fe(Zn) substrate

Astrometry with The \u3cem\u3eHubble Space Telescope\u3c/em\u3e: A Parallax of the Central Star of the Planetary Nebula NGC 6853

We present an absolute parallax and relative proper motion for the central star of the planetary nebula NGC 6853 (the Dumbbell). We obtain these with astrometric data from the Fine Guidance Sensor 3, a white-light interferometer on the Hubble Space Telescope. Spectral classifications and VRIJHKT2M and DDO51 photometry of the stars making up the astrometric reference frame provide spectrophotometric estimates of their absolute parallaxes. Introducing these into our model as observations with error, we find πabs = 2.10 ± 0.48 mas for the DAO central star of NGC 6853. A weighted average with a previous ground-based USNO determination yields πabs = 2.40 ± 0.32. We assume that the extinction suffered by the reference stars nearest (in angular separation and distance) to the central star is the same as for the central star. Correcting for color differences, we find AV = 0.30 ± 0.06 for the central star, hence, an absolute magnitude MV = 5.48. A recent determination of the central star effective temperature aided in estimating the central star radius, R* = 0.055 ± 0.02 R⊙, a star that may be descending to the white dwarf cooling track

The role of parental achievement goals in predicting autonomy-supportive and controlling parenting

Although autonomy-supportive and controlling parenting are linked to numerous positive and negative child outcomes respectively, fewer studies have focused on their determinants. Drawing on achievement goal theory and self-determination theory, we propose that parental achievement goals (i.e., achievement goals that parents have for their children) can be mastery, performance-approach or performance-avoidance oriented and that types of goals predict mothers' tendency to adopt autonomy-supportive and controlling behaviors. A total of 67 mothers (aged 30-53 years) reported their goals for their adolescent (aged 13-16 years; 19.4 % girls), while their adolescent evaluated their mothers' behaviors. Hierarchical regression analyses showed that parental performance-approach goals predict more controlling parenting and prevent acknowledgement of feelings, one autonomy-supportive behavior. In addition, mothers who have mastery goals and who endorse performance-avoidance goals are less likely to use guilt-inducing criticisms. These findings were observed while controlling for the effect of maternal anxiety