Alan W. Irwin

Faulty environments and risk reasoning: the local understanding of industrial hazards

Building upon a detailed empirical analysis of the local understanding of hazards in one geographical area, in this paper we offer a critique of both the psychometric and ‘risk society’ approaches to the relationship between lay and scientific groups. Specifically, we explore the connection between lay understandings of risk and the contexts of their development and application with regard to one industrial hazard site in northeast England. Rather than presenting local knowledges as fixed or separable from cultural practices and social worldviews, we examine the relational and active construction of environmental understandings—noting the significance of such factors as local memory, observation and evidence, definitions of expertise, risk and credibility, and moral discourses. The paper concludes with a discussion of the relationship between knowledge, understanding, and context. We also consider the wider significance of this case study both for environmental policy and for more theoretical treatments of science and its publics.

Evidence for a Long-Period Planet Orbiting ϵ Eridani*

High-precision radial velocity (RV) measurements spanning the years 1980.8‐2000.0 are presented for the nearby (3.22 pc) K2 V star e Eri. These data, which represent a combination of six independent data sets taken with four different telescopes, show convincing variations with a period of …7 yr. A least-squares orbital solution using robust estimation yields orbital parameters of period yr, velocity amplitude m s 21 , ecP p 6.9 K p 19 centricity , projected companion mass , and semimajor axis

The initial helium content of Galactic globular cluster stars from the R-parameter : Comparison with the cosmic microwave background constraint

Recent precise determinations of the primordial He abundance (Yp) from cosmic microwave background (CMB) analyses and cosmological nucleosynthesis computations provide Yp = 0.248 ± 0.001. On the other hand, recent works on the initial He abundance of Galactic globular cluster (GGC) stars, making use of the R-parameter as an He indicator, have consistently obtained YGGC ~ 0.20. In light of this serious discrepancy, which casts doubt on the adequacy of low-mass He-burning stellar models, we have rederived the initial He abundance for stars in two large samples of GGCs by employing theoretical models computed using new and more accurate determinations of the equation of state for the stellar matter and of the uncertain 12C(α,γ)16O reaction rate. Our models include semiconvection during the central convective He-burning phase, while the breathing pulses are suppressed, in agreement with the observational constraints coming from the measurements of the R2-parameter in a sample of clusters. By taking into account the observational errors on the individual R-parameter values, as well as uncertainties in the GGC [Fe/H] scale, treatment of convection, and 12C(α,γ)16O reaction rate, we have obtained a mean YGGC = 0.243 ± 0.006 and YGGC = 0.244 ± 0.006 for the two studied GGC samples. These estimates are now fully consistent with Yp obtained from CMB studies. Moreover, the trend of the individual He abundances with respect to [Fe/H] is consistent with no appreciable He enrichment along the GGC metallicity range.

Yellow giants - A new class of radial velocity variable

The five K giants and one K supergiant included in a precise (HF) radial velocity program all show significant long-term (about 1 yr), low-amplitude (30-300 m/s rms) radial velocity variations which make them unsuitable as precise radial velocity standars. Arcturus has been discussed in detail elsewhere, and the supergiant Epsilon Peg is probably a semiregular variable. The sampling in the five years of data is inadequate to say whether the giants are related to the Cepheid or Mira variables or form an independent class. The amplitudes of the long-term radial velocity variations of the giants and supergiant are correlated with the level of chromospheric activity shown by K line emission intensity and its fluctuation as seen in He I 10830-A. 19 refs.

The orbit and mass of Procyon

We have determined the orbit and parallax of the Procyon system (F5 IV-V primary and white dwarf secondary) using conventional absolute radial velocities, precise relative radial velocities determined with the hydrogen flouride (HF) absorption-cell technique, and astrometric and visual observations. Our least-squares analysis confirms and strengthens Strands previous analysis based on more limited material. We derive an absolute parallax of piabs=0.2899 ± 0.0074 arcsec. Our parallax result is in excellent agreement with other parallax investigations based on independent material. If we adopt the latest USNO parallax of piabs=0.2864 ± 0.0023 arcsec, then from our orbital paramters we derive MA=1.751 ± 0.051 solar mass, and MB=0.622 ± 0.017 solar mass. For the derived mass of Procyon A (which is consistent with previous results), it has long been known that the luminosity predicted by stellar interior theory is approximately a factor of two larger than the luminosity derived from observations. The errors in this observed luminosity and the above formal standard errors (i.e., our best estimates of the statistical random errors) in our derived mass are too small to explain this discrepancy. If the observed separation of the binary components has been systematically overestimated by approximately 0.2 arcsec, then the derived mass would be reduced, thus resolving the discrepancy. However, the excellent consistency of the separations measured by Aitken and Barnard for a number of years at different sites argues against this interpretation. The stellar interior theory of Procyon A may need substantial revision.

Long-period radial-velocity variations of Arcturus

Precise measurements of the radial velocity of Arcturus were obtained on 43 occasions between 1981 and 1985. The measurements show a 500 m/s range, confirming the radial velocity variability of Arcturus. Multiperiod models which give a good representation of the velocities are derived using a least-squares technique. The models also fit the velocities of Smith et al. (1987). It is suggested that the small-amplitude short-period components of the models could be analogous to the solar five-minute oscillations. The best-fitting models require the largest-amplitude component to have a period of at least 640 days.

The prediction of stellar effective temperatures from the mixing-length theory of convection

A generalized version of the mixing-length theory (MLT) of convection, along with simplifications in the limits of high and low convective efficiency, is described. This forms the basis for a study of the effects of proposed modifications to the original (Boehm-Vitense, 1958) form of the MLT on the predicted effective temperatures of cool stars. These modifications include the parameters y and m. It is found that none of the suggested refinements to the MLT affect the location and shape of an evolutionary track on the H-R diagram in ways that cannot be mimicked to high accuracy by a suitable choice of mixing length parameters alone. Thus, if mixing length parameters is calibrated by comparing stellar models with observed main-sequence stars with well-determined properties, then the subsequent evolutionary tracks and isochrones are uniquely defined, regardless of what version of the MLT is used in the calculations. A careful examination of the Revised Yale Isochrones suggests that the Teff scale of these isochrones is inconsistent with the assumed MLT, thereby resolving much of the known discrepancies between these calculations and those of VandenBerg and Bell (1958). 44 refs.

A CA II LAMBDA-8662 INDEX OF CHROMOSPHERIC ACTIVITY: THE CASE OF 61 CYGNI A

The stellar spectra obtained in our precise velocity program include the Ca II infrared triplet line at lambda-8662. Changes in the core flux of this line, quantified with our Delta-EW8662 index, reflect changes in stellar chromospheric activity. In our 12 years of Ca II observations for 61 Cygni A, we detect a solar-type cycle of 7.22 years and a rotational period of 36.21 days which confirm earlier results based on the H and K lines. The stability of the derived rotation period over 12 years suggests that the regions of chromospheric activity are either long-lived or formed within a limited-longitudal range.

A LOW-AMPLITUDE PERIODICITY IN THE RADIAL VELOCITY AND CHROMOSPHERIC EMISSION OF BETA GEMINORUM

Using high-quality spectra obtained with the hydrogren fluoride technique at the Canada-France-Hawaii 3.6-meter telescope and Dominion Astrophysical Observatory 1.22-meter telescope, we have detected a low-amplitude periodicity in both the radial velocity and chromospheric emission of Beta Geminorum. In addition, we have detected a long-term change (time scale > 12 years) in thi stars chromospheric emission which is reminiscent of solar-type magnetic cycles believed present in giants of similar spectral type. The radial-velocity variations can be fitted by a sinusoid with amplitude and period of K = 46.23 ± 3.9 m s-1, P=584.65 ± 3.3 days. A similar, statistically significant (false-alarm probability of 1%) period is found in the residuals from the long-term trend in the chromospheric emission: P = 587.7 ± 12 days. However, because of the weakness of the signal, K = 0.583 ± 19 mA, this detection needs confirmation. Although these independently determined periods are in agreement with each other, they are not consistent with the maximum rotation period of 178 days derived from this stars v sin i = 2.5 km s-1 (Gray 1982). Either the observed v sin i value of Beta Geminorum needs to be revised below 0.76 km s-1 or some alternative to rotational modulation of surface phenomena must be found to explain this stars periodicity.

36 OPHIUCHI AB: INCOMPATIBILITY OF THE ORBIT AND PRECISE RADIAL VELOCITIES

The long-period (~600 yr) binary system 36 Ophiuchi AB consists of two chromospherically active K dwarfs. If we constrain the period using the mass-luminosity relation and the observed parallax, the remaining orbit parameters can be estimated from the 170 years of visual-binary observations. In this paper, we further constrain the orbit by precise measurements of the differential radial velocities (with arbitrary zero points) of both 36 Oph A and B and the difference in radial velocity between 36 Oph B and A. Our best orbit gives a good fit to the visual-binary observations, the difference in velocity, and the mean radial acceleration of A; but the observed acceleration of B is a factor of 164 larger than the value predicted by the orbit. This factor is so large that no reasonable variation in the adopted sum of masses, mass ratio, parallax, or orbit parameters will remove the B acceleration discrepancy. Ths maximum companion mass allowed by the residuals from the visual-binary orbit is of order 8 Jupiter masses for assumed periods between 30 and 100 years so the 36 Oph B acceleration discrepancy would ordinarily make it a candidate for a substellar companion. However, the very high eccentricity (~0.9) of the binary-star orbit means its closest approach is of order 6 a.u. making it unlikely that any substellar companions would form or survive with the semi-major axis exceeding ~1.5 a.u. or period exceeding ~2 years. Thus, 36 Oph B is an important counter-example which serves as a warning that for chromospherically active stars, at least, it is possible to have apparent radial accelerations in the absence of substellar companions.