Spectropolarimetry with the DAO 1.8-m telescope

The fast-switching DAO spectropolarimeter mounted on the 1.8-m Plaskett telescope started operation in 2007. Almost 14,000 medium-resolution (R=15,000) polarimetric spectra of 65 O - F type stars have been obtained since then in the course of three ongoing projects: the DAO Magnetic Field Survey, supporting observations for the CFHT MiMeS survey, and an investigation of the systematic differences between the observed longitudinal field measured with the Hbeta line and metallic lines. The projects are briefly described here. The current status as well as some results are presented.Comment: "Magnetic Stars", Proceedings of the International Conference, Nizhny Arkhyz, 27 August - 1 September 201

Abundance And Magnetic Field Geometries Of The Helium-strong Stars

High signal-to-noise coude reticon spectra of five helium-strong stars have been obtained in two spectral regions ({dollar}\lambda\lambda{dollar}3980-4160 and {dollar}\lambda\lambda{dollar}4400-4580) at the Canada-France-Hawaii Telescope, Mauna Kea, Hawaii. Phase-resolved sets of spectra have been obtained for the magnetic-variable stars {dollar}\sigma{dollar} Ori E, HD 37776, and HD 64740. Additional observations have also been made of the sharp-lined helium-strong stars HD 58260 and {dollar}\delta{dollar} Ori C. These data, and additional Zeeman analyzer observations, have been used in an attempt to determine the magnetic field geometries and abundance distributions of the program stars. The models have been obtained by use of a line synthesis program that incorporates the effects of an assumed magnetic field and abundance distribution into the calculation of line profiles.;Helium line profile variations of HD 64740 may be modelled with two spots with anomalously high helium abundances near the magnetic poles of the star. Silicon, appears to have a large abundance in a high latitude band around the star. The surface magnetic field of HD 64740 is not strong enough to cause magnetic intensification effects in the Si III multiplet 2 line profiles.;The peculiar, broad helium line profiles of {dollar}\delta{dollar} Ori C suggest two possible helium abundance geometries for the star. A helium-rich spot near the visible magnetic pole of an otherwise extremely helium-poor star, and a vertical helium abundance gradient are both able to reproduce the observed profiles of the star. The second non-variable program star, HD 58260, also shows marginal evidence for such an abundance geometry.;The helium line profiles of {dollar}\sigma{dollar} Ori E are reproduced with two spots of large helium abundance ({dollar}\epsilon\sb{lcub}\rm He{rcub}{dollar} {dollar}\u3e{dollar} 0.5) near the intersections of the magnetic and rotation equators of the star. Silicon, magnesium, nitrogen, and oxygen all appear to be overabundant in a high latitude band on the surface of the star. Observations of the variable H{dollar}\alpha{dollar} emission of the star are presented.;A theoretical model for the peculiar longitudinal magnetic field variations of HD 37776 is proposed. The model consists of colinear dipole, quadrupole, and octupole field components that result in a magnetic field that varies between 20 and 60 kG over the surface of the star. Helium and silicon abundance geometries consistent with equatorial and polar distributions of the respective elements support the field model, as do the pronounced differential magnetic intensification effects seen in the silicon lines.;Several suggestions for interesting future observational and theoretical work are discussed

Photoreactivation of Lethal Damage Induced in Hamster X Xenopus Hybrid Cells and Their Parentals by UV Light

A85 Xenopus cells that exhibited a high level of photoreactivation (PR) and V79B2 hamster cells that exhibited little PR were fused to produce the V79B2 x A85 cell line — a hybrid line which possessed a relatively stable karyotype, with most cells containing the entire V79B2 and A85 genomes. UV and UV plus PR fluence-survival relations were then determined and compared for the hybrid and parental lines in a first attempt to elucidate interactions of the parental PR mechanisms in the hybrid. It was anticipated that the A85 genome in the hybrid would produce PR enzyme in sufficient concentration and of such a nature as to efficiently PR UV-induced lethal damage in both A85 and V79B2 DNA, and little difference would be observed in the levels of PR exhibited by the V79B2 x A85 and A85 lines. To the contrary, the level of PR observed for the hybrid was substantially below that observed for the A85 line. To assist in the interpretation of this unexpected observation, three additional preliminary studies were carried out: 1) Comparison of the optimum PR schemes for the A85 and hybrid lines, 2) examination of relations between the PR and dark UV repair mechanisms possessed by these lines, and 3) comparison of the levels of PR of chromatid deletions induced by UV in selected V79B2 and A85 chromosomes of the hybrid. The results suggested that the relatively low level of PR manifested by the hybrid cells was a consequence of their inability to efficiently PR pyrimidine dimers induced by UV in V79B2 DNA

Studies of Variability in Proto-Planetary Nebulae: II. Light and Velocity Curve Analyses of Iras 22272+5435 and 22223+4327

We have carried out a detailed observational study of the light, color, and velocity variations of two bright, carbon-rich proto-planetary nebulae, IRAS 22223+4327 and 22272+5435. The light curves are based upon our observations from 1994 to 2011, together with published data by Arkhipova and collaborators. They each display four significant periods, with primary periods for IRAS 22223+4327 and 22272+5435 being 90 and 132 days, respectively. For each of them, the ratio of secondary to primary period is 0.95, a value much different from that found in Cepheids, but which may be characteristic of post-AGB stars. Fewer significant periods are found in the smaller radial velocity data sets, but they agree with those of the light curves. The color curves generally mimic the light curves, with the objects reddest when faintest. A comparison in seasons when there exist contemporaneous light, color, and velocity curves reveals that the light and color curves are in phase, while the radial velocity curves are 0.25 out of phase with the light curves. Thus they differ from what is seen in Cepheids, in which the radial velocity curve is 0.50 P out of phase with the light curve. Comparison of the observed periods and amplitudes with those of post-AGB pulsation models shows poor agreement, especially for the periods, which are much longer than predicted. These observational data, particularly the contemporaneous light, color, and velocity curves, provide an excellent benchmark for new pulsation models of cool stars in the post-AGB, proto-planetary nebula phase.Comment: 15 Figures plus Erratu

Where Are the Binaries? Results of a Long-Term Search for Radial Velocity Binaries in Proto-Planetary Nebulae

We present the results of an expanded, long-term radial velocity search (25 yrs) for evidence of binarity in a sample of seven bright proto-planetary nebulae (PPNe). The goal is to investigate the widely-held view that the bipolar or point-symmetric shapes of planetary nebulae (PNe) and PPNe are due to binary interactions. Observations from three observatories were combined from 2007-2015 to search for variations on the order of a few years and then combined with earlier observations from 1991-1995 to search for variations on the order of decades. All seven show velocity variations due to periodic pulsation in the range of 35-135 days. However, in only one PPN, IRAS 22272+5435, did we find even marginal evidence found for multi-year variations that might be due to a binary companion. This object shows marginally-significant evidence of a two-year period of low semi-amplitude which could be due to a low-mass companion, and it also displays some evidence of a much longer period of >30 years. The absence of evidence in the other six objects for long-period radial velocity variations due to a binary companion sets significant constraints on the properties of any undetected binary companions: they must be of low mass, 30 years. Thus the present observations do not provide direct support for the binary hypothesis to explain the shapes of PNe and PPNe and severely constrains the properties of any such undetected companions.Comment: 28 pages, 5 figure

Modulation of Ca II H & K Emission by Short-Period Planets

We have detected modulation of the Ca II H&K reversal structure in four out of five 51 Peg-type stars whose planets have orbital periods between 3 and 4 days. We observe two effects in the K-core: (1) a broad 3-A variation at ~1% level and (2) changes on a scale of 0.5 A (~1-3%) in each of the three reversal features. The nightly variations are coherent in both H and K. From differential radial velocities measured to better than 20 m/s, up-to-date phases were extracted. The enhancements in the reversals tend to be greatest at the sub-planetary points which may imply that there is a magnetic interaction between the star's outer layers and the magnetosphere of the planet. These high-S/N (500 per pixel in the continuum) and high-resolution (R = 110,000) data are too few to confirm orbital synchronization.Comment: 4 pages, 2 figures, in newpasp.sty format. To be published by PASP (ed. Drake Deming) in the proceedings of the conference entitled "Scientific Frontiers in Research on Extrasolar Planets," held at the Carnegie Institution of Washington, DC, June 18-21, 200

HD 35502: a hierarchical triple system with a magnetic B5IVpe primary

We present our analysis of HD~35502 based on high- and medium-resolution spectropolarimetric observations. Our results indicate that the magnetic B5IVsnp star is the primary component of a spectroscopic triple system and that it has an effective temperature of $18.4\pm0.6\,{\rm kK}$, a mass of $5.7\pm0.6\,M_\odot$, and a polar radius of $3.0^{+1.1}_{-0.5}\,R_\odot$. The two secondary components are found to be essentially identical A-type stars for which we derive effective temperatures ($8.9\pm0.3\,{\rm kK}$), masses ($2.1\pm0.2\,M_\odot$), and radii ($2.1\pm0.4\,R_\odot$). We infer a hierarchical orbital configuration for the system in which the secondary components form a tight binary with an orbital period of $5.66866(6)\,{\rm d}$ that orbits the primary component with a period of over $40\,{\rm yrs}$. Least-Squares Deconvolution (LSD) profiles reveal Zeeman signatures in Stokes $V$ indicative of a longitudinal magnetic field produced by the B star ranging from approximately $-4$ to $0\,{\rm kG}$ with a median uncertainty of $0.4\,{\rm kG}$. These measurements, along with the line variability produced by strong emission in H$\alpha$, are used to derive a rotational period of $0.853807(3)\,{\rm d}$. We find that the measured $v\sin{i}=75\pm5\,{\rm km\,s}^{-1}$ of the B star then implies an inclination angle of the star's rotation axis to the line of sight of $24^{+6}_{-10}\degree$. Assuming the Oblique Rotator Model, we derive the magnetic field strength of the B star's dipolar component ($14^{+9}_{-3}\,{\rm kG}$) and its obliquity ($63\pm13\degree$). Furthermore, we demonstrate that the calculated Alfv\'{e}n radius ($41^{+17}_{-6}\,R_\ast$) and Kepler radius ($2.1^{+0.4}_{-0.7}\,R_\ast$) place HD~35502's central B star well within the regime of centrifugal magnetosphere-hosting stars.Comment: 24 pages, 14 figures, Accepted for publication in MNRA

Evidence for Planet-induced Chromospheric Activity on HD 179949

We have detected the synchronous enhancement of Ca II H & K emission with the short-period planetary orbit in HD 179949. High-resolution spectra taken on three observing runs extending more than a year show the enhancement coincides with phi ~ 0 (the sub-planetary point) of the 3.093-day orbit with the effect persisting for more than 100 orbits. The synchronous enhancement is consistent with planet-induced chromospheric heating by magnetic rather than tidal interaction. Something which can only be confirmed by further observations. Independent observations are needed to determine whether the stellar rotation is sychronous with the planet's orbit. Of the five 51 Peg-type systems monitored, HD 179949 shows the greatest chromospheric H & K activity. Three others show significant nightly variations but the lack of any phase coherence prevents us saying whether the activity is induced by the planet. Our two standards, tau Ceti and the Sun, show no such nightly variations.Comment: 10 pages, 6 figures. Submitted to Ap

The Radial Velocity Precision of Fiber-fed Spectrographs

We have measured the radial velocities of five 51 Peg-type stars and one star with constant velocity. Our measurements, on 20 \AA centered at 3947 \AA, were conventional using Th/Ar comparison spectra taken every 20 or 40 minutes between the stellar exposures. Existing IRAF routines were used for the reduction. We find $\sigma_{RV}$ $\leq$ 20 m s$^{-1}$, provided 4 measurements (out of 72) with residuals $>5\sigma_{RV}$ are neglected. The observations were made with the CFHT Gecko spectrograph, fiber-fed with the CAFE system (R$\sim$110,000). $\sigma_{RV}$ $\leq$10 m s$^{-1}$ seems possible with additional care. This study was incidental to the main program and so not exhaustive but the small value of $\sigma_{RV}$ implies that the fiber feed/image slicer system on Gecko + CAFE, essentially eliminates the long standing problem of guiding errors in radial velocity measurements. We are not suggesting this conventional approach for serious Doppler planet searches (especially with Gecko which has such a small multiplex gain), but the precision is valuable for observations made in spectral regions remote from telluric lines or captive-gas fiducials. Instrument builders might consider the advantages of the CAFE optics which incorporate agitation and invert the object and pupil for slit and grating illumination in future spectrograph designs.Comment: 12 pages, 3 figure