Magnetism, rotation and accretion in Herbig Ae-Be stars

Studies of stellar magnetism at the pre-main sequence phase can provide important new insights into the detailed physics of the late stages of star formation, and into the observed properties of main sequence stars. This is especially true at intermediate stellar masses, where magnetic fields are strong and globally organised, and therefore most amenable to direct study. This talk reviews recent high-precision ESPaDOnS observations of pre-main sequence Herbig Ae-Be stars, which are yielding qualitatively new information about intermediate-mass stars: the origin and evolution of their magnetic fields, the role of magnetic fields in generating their spectroscopic activity and in mediating accretion in their late formative stages, and the factors influencing their rotational angular momentum.Comment: 8 page

Spectropolarimetry of the H-alpha line in Herbig Ae/Be stars

Using the HiVIS spectropolarimeter built for the Haleakala 3.7m AEOS telescope, we have obtained a large number of high precision spectropolarimetrc observations (284) of Herbig AeBe stars collected over 53 nights totaling more than 300 hours of observing. Our sample of five HAeBe stars: AB Aurigae, MWC480, MWC120, MWC158 and HD58647, all show systematic variations in the linear polarization amplitude and direction as a function of time and wavelength near the H-alpha line. In all our stars, the H-alpha line profiles show evidence of an intervening disk or outflowing wind, evidenced by strong emission with an absorptive component. The linear polarization varies by 0.2% to 1.5% with the change typically centered in the absorptive part of the line profile. These observations are inconsistent with a simple disk-scattering model or a depolarization model which produce polarization changes centered on the emmissive core. We speculate that polarized absorption via optical pumping of the intervening gas may be the cause.Comment: Accepted for publication in ApJ Letter

Discovery of a strong magnetic field on the O star HD 191612: new clues to the future of theta1 Orionis C?

From observations made with the ESPaDOnS spectropolarimeter, recently installed on the 3.6-m Canada--France--Hawaii Telescope, we report the discovery of a strong magnetic field in the Of?p spectrum variable HD 191612 -- only the second known magnetic O star (following theta1 Ori C). The stability of the observed Zeeman signature over four nights of observation, together with the non-rotational shape of line profiles, argue that the rotation period of HD 191612 is significantly longer than the 9-d value previously proposed. We suggest that the recently identified 538-d spectral-variability period is the rotation period, in which case the observed line-of-sight magnetic field of -220+-38 G implies a large-scale field (assumed dipolar) with a polar strength of about -1.5 kG. If confirmed, this scenario suggests that HD 191612 is, essentially, an evolved version of the near-ZAMS magnetic O star theta1 Ori C, but with an even stronger field (about 15 kG at an age similar to that of theta1Ori C). We suggest that the rotation rate of HD 191612, which is exceptionally slow by accepted O-star standards, could be due to angular-momentum dissipation through a magnetically confined wind.Comment: Accepted by MNRAS Letters, 5 pages, 2 figures, 2 table

The PLATO End-to-End CCD Simulator -- Modelling space-based ultra-high precision CCD photometry for the assessment study of the PLATO Mission

The PLATO satellite mission project is a next generation ESA Cosmic Vision satellite project dedicated to the detection of exo-planets and to asteroseismology of their host-stars using ultra-high precision photometry. The main goal of the PLATO mission is to provide a full statistical analysis of exo-planetary systems around stars that are bright and close enough for detailed follow-up studies. Many aspects concerning the design trade-off of a space-based instrument and its performance can best be tackled through realistic simulations of the expected observations. The complex interplay of various noise sources in the course of the observations made such simulations an indispensable part of the assessment study of the PLATO Payload Consortium. We created an end-to-end CCD simulation software-tool, dubbed PLATOSim, which simulates photometric time-series of CCD images by including realistic models of the CCD and its electronics, the telescope optics, the stellar field, the pointing uncertainty of the satellite (or Attitude Control System [ACS] jitter), and all important natural noise sources. The main questions that were addressed with this simulator were the noise properties of different photometric algorithms, the selection of the optical design, the allowable jitter amplitude, and the expected noise budget of light-curves as a function of the stellar magnitude for different parameter conditions. The results of our simulations showed that the proposed multi-telescope concept of PLATO can fulfil the defined scientific goal of measuring more than 20000 cool dwarfs brighter than mV =11 with a precision better than 27 ppm/h which is essential for the study of earth-like exo-planetary systems using the transit method.Comment: 5 pages, submitted for the Proceedings of the 4th HELAS International Conference: Seismological Challenges for Stellar Structur

The dramatic change of the fossil magnetic field of HD 190073: evidence of the birth of the convective core in a Herbig star ?

In the context of the ESPaDOnS and Narval spectropolarimetric surveys of Herbig Ae/Be stars, we discovered and then monitored the magnetic field of HD 190073 over more than four years, from 2004 to 2009. Our observations all displayed similar Zeeman signatures in the Stokes V spectra, indicating that HD 190073 hosted an aligned dipole, stable over many years, consistent with a fossil origin. We obtained new observations of the star in 2011 and 2012 and detected clear variations of the Zeeman signature on timescales of days to weeks, indicating that the configuration of its field has changed between 2009 and 2011. Such a sudden change of external structure of a fossil field has never previously been observed in any intermediate or high-mass star. HD 190073 is an almost entirely radiative pre-main sequence star, probably hosting a growing convective core. We propose that this dramatic change is the result of the interaction between the fossil field and the ignition of a dynamo field generated in the newly-born convective core.Comment: 4 pages, 5 figures, accepted for publication in A&

Characterisation of the magnetic field of the Herbig Be star HD 200775

After our recent discovery of four magnetic Herbig stars, we have decided to study in detail one of them, HD 200775, to determine if its magnetic topology is similar to that of the main sequence magnetic stars. With this aim, we monitored this star in Stokes I and V over more than two years, using the new spectropolarimeters ESPaDOnS at CFHT, and Narval at TBL. Using our data, we find that HD 200775 is a double-lined spectroscopic binary system, whose secondary seems similar, in temperature, to the primary. We determine the luminosity ratio of the system, and using the luminosity of the system found in literature, we derive the luminosity of both stars. From our measurements of the radial velocities of both stars we determine the ephemeris and the orbital parameters of the system. We have fitted 30 Stokes V profiles simultaneously, using a chi2 minimisation method, with a decentered-dipole model. The best-fit model provides a rotation period of 4.3281 d an inclination angle of 60 degrees, and a magnetic obliquity angle of 125 degrees. The polar strength of the magnetic dipole field is 1000 G, which is decentered by 0.05 R* from the center of the star. The derived magnetic field model is qualitatively identical to those commonly observed in the Ap/Bp stars, which bring strong argument in favour of the fossil field hypothesis, to explain the origin of the magnetic fields in the main sequence Ap/Bp stars. Our determination of the inclination of the rotation axis leads to a radius of the primary which is smaller than that derived from the HR diagram position. This can be explained by a larger intrinsic luminosity of the secondary relative to the primary, due to a larger circumstellar extinction of the secondary relative to the primary.Comment: Accepted for publication in MNRAS, 14 pages, 10 figure

Patterns of antenal sensilla of Panstrongylus megistus from three Brazilian states

The objective of the present study was to analyze and describe the phenotype of the antennal sensilla of Panstrongylus megistus, one of the epidemiologically most important species of triatomines in Brazil. Specimens from the Brazilian states of Goiás (GO), Minas Gerais (MG), and Rio Grande do Sul (RS) were compared, based on studies of four types of sensilla on three antennal segments: thick-walled trichoid (TK), thin-walled trichoid (TH), bristles (BR), and basiconica (BA). Discriminant analysis allowed the separation of the RS specimens from those of GO and MG. Multivariate discriminant analysis demonstrated that the sensilla of males differed from those of females, the variables with greatest weight being the BA of all three segments and the TK of flagellum 1. The basiconica sensilla were significantly more abundant in females, on all three segments. Antennal sensilla patterns also demonstrated significant differences among P. megistus specimens.Fil: Villela, M. M.. Fundación Oswaldo Cruz; BrasilFil: Catala, Silvia Susana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja. - Universidad Nacional de La Rioja. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja. - Universidad Nacional de Catamarca. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja. - Secretaría de Industria y Minería. Servicio Geológico Minero Argentino. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja. - Provincia de La Rioja. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja; ArgentinaFil: Juberg, J.. Instituto Oswaldo Cruz; Brasil. Fundación Oswaldo Cruz; BrasilFil: Silva, I. G.. Universidade Federal de Goiás; BrasilFil: Dias, J. C. P.. Fundación Oswaldo Cruz; Brasi