Side reactions during the initiation step in oligomerization of methacrylic esters by electron transfer reaction

Catala, J.‐M.; Clauss, Margot

doi:10.1002/macp.1992.021930903

Cited by 10 publications

(13 citation statements)

References 16 publications

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“…Considering the very large widths of both components, it is clear that they are formed in regions of high macrotur bulent motions; these motions can reach several hundreds kms-1, a value consistent with previous estimates (Catala & Kunasz 1987;Catala 1988;Catala et al 1993). We sug gest the following interpretation of the behavior of both components of the He 15876 Â line:…”

Section: Discussionsupporting

confidence: 90%

Azimuthal structures in the wind and chromosphere of the Herbig Ae star AB Aurigae. Results from the MUSICOS 1992 campaign

Böhm

Catala

Donati

et al. 1996

Astron. Astrophys. Suppl. Ser.

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Abstract. -The observations of the MUSICOS 1992 campaign concerned three scientific programs, among which was the study of azimuthal structures in the wind and chromosphere of the pre-main sequence Herbig Ae star AB Aur. The He 15876 Â line of AB Aur, which is formed in the expanding chromosphere of this star, most probably in the innermost parts of its wind, was continuously monitored at a spectral resolution of 30000 for about 4 days. The line was discovered to be variable in a spectacular way, the profile changing from pure emission to a composite profile including a deep absorption component in the course of a few hours. In this paper we present strong clues that suggest a rotational modulation of the line, with a period corresponding to the stars rotation period of 32 hrs. We confirmed the covariation of several non-photospheric spectral lines, formed at very different radial distances of the star, which strengthens the idea that the variability is the signature of azimuthal structures in the wind of AB Aur, most probably due to magnetically confined streams or loops emanating from the stellar surface. We present the data collected during the MUSICOS 1992 campaign, but also a data set of the Hel D3 line obtained with FOE at KPNO during the years 1991-1994 and a series of IUE spectra containing the Mgllh&k UV lines obtained one month prior to the campaign. A thorough discussion of the possible interpretations of the spectacular variations of the He I 5876 Å line is presented.

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Section: Discussionsupporting

confidence: 90%

Azimuthal structures in the wind and chromosphere of the Herbig Ae star AB Aurigae. Results from the MUSICOS 1992 campaign

Böhm

Catala

Donati

et al. 1996

Astron. Astrophys. Suppl. Ser.

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“…Weaker lines, which are formed deeper in the atmosphere, have no contribution from the heated region, presumably located too high above the star's surface. A heated region at the base of the wind has been frequently invoked to explain a few strong emission lines and lines of superionized species in the spectra of several Herbig Ae/Be stars (Catala & Talavera 1984;Catala 1988;Bouret & Catala 1998). In the case of HD 190073, where a much larger number of lines are seen in emission, the heated region just needs to be of higher density than in these other less extreme cases.…”

Section: Discussionmentioning

confidence: 99%

The magnetic field of the pre-main sequence Herbig Ae star HD 190073

Catala¹,

Alécian²,

Donati

et al. 2006

A&A

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Context. The general context of this paper is the study of magnetic fields in the pre-main sequence intermediate mass Herbig Ae/Be stars. Magnetic fields are likely to play an important role in pre-main sequence evolution at these masses, in particular in controlling the gains and losses of stellar angular momentum. Aims. The particular aim of this paper is to announce the detection of a structured magnetic field in the Herbig Ae star HD 190073, and to discuss various scenarii for the geometry of the star, its environment and its magnetic field. Methods. We have used the ESPaDOnS spectropolarimeter at CFHT in 2005 and 2006 to obtain high-resolution, high signal-to-noise circular polarization spectra which demonstrate unambiguously the presence of a magnetic field in the photosphere of this star. Results. Nine circular polarization spectra were obtained, each one showing a clear Zeeman signature. This signature is suggestive of a magnetic field structured on large scales. The signature, which corresponds to a longitudinal magnetic field of 74 ± 10 G, does not vary detectably on a one-year timeframe, indicating either an azimuthally symmetric field, a zero inclination angle between the rotation axis and the line of sight, or a very long rotation period. The optical spectrum of HD 190073 exhibits a large number of emission lines. We discuss the formation of these emission lines in the framework of a model involving a turbulent heated region at the base of the stellar wind, possibly powered by magnetic accretion. Conclusions. This magnetic detection contributes an important new observational discovery which will aid our understanding of stellar magnetism at intermediate masses.

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“…Short-term variability of many of these lines are observed and P Cygni profiles of Hα, Hβ, Mg II h and k lines present in the spectra of some of these stars indicate the presence of strong and structured stellar winds (see e.g. Praderie et al 1982Praderie et al , 1986Catala & Talavera 1984;Catala et al 1986a,b;Catala & Kunasz 1987;Catala 1988;Böhm & Catala 1995;Böhm et al 1996).…”

Section: Introductionmentioning

confidence: 99%

Spectroscopic monitoring of the Herbig Ae star HD 104237

Fumel

Boehm

2012

A&A

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Context. Herbig Ae/Be stars are intermediate-mass pre-main sequence (PMS) stars showing signs of intense activity and strong stellar winds, whose origin is not yet understood in the frame of current theoretical models of stellar evolution for young stars. In addition, the evolutionary tracks of the earlier Herbig Ae stars cross the theoretical PMS instability strip located roughly in the same area of the HR diagram as the δ Scuti variables. Many of these stars exhibit pulsations of δ Scuti type. Aims. Understanding the internal structure of pulsating Herbig Ae stars based on asteroseismic studies will help constraining the origin of their tremendous activity, winds, and variability. It is therefore necessary to investigate the location of the PMS instability strip and of its boundaries, and to extend the sample of observed and studied pulsating Herbig Ae stars. The aim of this work was to carry out a thorough analysis of the line profile variations of the prototype Herbig Ae star HD 104237 based on high-resolution spectroscopy and to redetermine precisely its fundamental parameters, which are the basic ingredients of a forthcoming asteroseismic modeling. Methods. HD 104237 is a pulsating Herbig Ae star with eight detected frequencies based on the analysis of radial velocity variations. In this article, we reinvestigated an extensive high-resolution quasi-continuous spectroscopic data set in order to search for very faint indications of non-radial pulsations in the line profile by working on dynamical spectra of equivalent photospheric (LSD) profiles of HD 104237. A 2D Fourier analysis (F2D) was performed of the entire profile and the temporal variation of the central depth of the line was studied with the time-series analysis tools Period04 and SigSpec. We present the results of these analysis including the mode identification corresponding to the detected dominant frequency, as well as a new determination of its fundamental stellar parameters.Results. The analysis of spectroscopic data set of April 22-25 obtained at SAAO in 1999 has confirmed the presence of multiple oscillation modes of low-degree in HD 104237 and led to the first direct detection of a non-radial pulsation mode in this star: the dominant mode F1 was identified by the Fourier 2D method having a degree value comprised between 1 and 2, the symmetry of the pattern variation indicating an azimuthal order of ±1. The detailed study of the fundamental stellar parameters has provided a T eff , log g, and iron abundance of 8550 ± 150 K, 3.9 ± 0.3, and −4.38 ± 0.19 (i.e. [Fe/H] = +0.16 ± 0.19 ), respectively.

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Side reactions during the initiation step in oligomerization of methacrylic esters by electron transfer reaction

Cited by 10 publications

References 16 publications

Azimuthal structures in the wind and chromosphere of the Herbig Ae star AB Aurigae. Results from the MUSICOS 1992 campaign

Azimuthal structures in the wind and chromosphere of the Herbig Ae star AB Aurigae. Results from the MUSICOS 1992 campaign

The magnetic field of the pre-main sequence Herbig Ae star HD 190073

Spectroscopic monitoring of the Herbig Ae star HD 104237

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