References of "Bohm, T"
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See detailFirst evidence of pulsations in Vega?. Results of today's most extensive spectroscopic search
Böhm, T.; Lignières, F.; Wade, G. et al

in Astronomy and Astrophysics (2012), 537

Context. The impact of rapid rotation on stellar evolution theory remains poorly understood as of today. Vega is a special object in this context as spectroscopic and interferometric studies have shown ... [more ▼]

Context. The impact of rapid rotation on stellar evolution theory remains poorly understood as of today. Vega is a special object in this context as spectroscopic and interferometric studies have shown that it is a rapid rotator seen nearly pole one, a rare orientation particularly interesting for seismic studies. In this paper, we present a first systematic search for pulsations in Vega. <BR /> Aims: The goal of the present work is to detect for the first time pulsations in a rapidly rotating star seen nearly pole-on. <BR /> Methods: Vega was monitored in quasi-continuous high-resolution echelle spectroscopy. A total of 4478 spectra were obtained. More precisely in 2008 we obtained 1213 spectra during 19.9 h on 3 nights (26th, 27th and 29th of July 2008) with NARVAL/TBL (at R = 65 000 and R = 75 000), in 2009 we obtained 1293 spectra during 13.7 h on 3 nights (9th-11th of September 2009) with ESPaDOnS/CFHT (at R = 68 000) and in 2010 we gathered again 1972 with NARVAL/TBL during 28.8 h on five nights (July 15th-19th). This data set should represent the most extensive high S/N, high resolution quasi-continuous survey obtained on Vega as of today. Least square deconvolved (LSD) profiles were obtained for each spectrum representing the photospheric absorption profile potentially deformed by the presence of pulsations. In addition, we calculated for each spectrum a telluric line LSD profile subsequently used as radial velocity reference. LSD profile centroids were adjusted and velocity differences (stellar-telluric) determined. These residual velocities were analysed and periodic low amplitude variations, potentially indicative of stellar pulsations, detected. In a subsequent step, the temporal line profile variations during the longest (2010) data set was calculated for each individual velocity bin of 1.8 km s[SUP]-1[/SUP] by computing a 2D (velocity-frequency) Lomb-Scargle periodogram. <BR /> Results: Based on high resolution echelle spectroscopy, we have obtained indications of periodic variations of very small amplitudes within the residual radial velocity curves of Vega. All three data sets revealed the presence of residual periodic variations: 5.32 and 9.19 d[SUP]-1[/SUP] (A ≈ 6 m s[SUP]-1[/SUP]) in 2008, 12.71 and 13.25 d[SUP]-1[/SUP] (A ≈ 8 m s[SUP]-1[/SUP]) in 2009 and 5.42 and 10.82 d[SUP]-1[/SUP] (A ≈ 3-4 m s[SUP]-1[/SUP]) in 2010. However, it is too early to conclude that the variations are due to stellar pulsations, and a confirmation of the detection with a highly stable spectrograph is a necessary next step. <BR /> Conclusions: If pulsations are confirmed, their very small amplitudes show that the star would belong to a category of very "quiet" pulsators. Based on observations obtained at the Bernard Lyot Telescope (TBL, Pic du Midi, France) of the Midi-Pyrénées Observatory, which is operated by the Institut National des Sciences de l'Univers (INSU) of the Centre National de la Recherche Scientifique of France (CNRS), and at the Canada-France-Hawaii Telescope (CFHT), which is operated by the National Research Council of Canada, INSU/CNRS and the University of Hawaii. [less ▲]

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See detailTowards a systematic spectroscopic characterization of pre-main sequence instability strip. Search for pulsations in three Herbig stars: V1247 Ori, HD35929 and HD 190073
Fumel, Aurélie ULg; Böhm, T; David, J

in Astronomy and Astrophysics (2012)

The origin of the strong activity and winds exhibited by Herbig Ae/Be stars is a still open question with regard to current young stellar evolutionary theory. On the supposition that this origin could be ... [more ▼]

The origin of the strong activity and winds exhibited by Herbig Ae/Be stars is a still open question with regard to current young stellar evolutionary theory. On the supposition that this origin could be internal, as growing evidences tend to indicate, probing Herbig stars interiors by means of the asteroseisomoly tool is therefore of great importance. The early-stage evolutionary tracks of the Herbig Ae stars cross the theoretical pre-main sequence (PMS) instability strip, that has to be spectroscopically characterized and whose boundaries and location, roughly in the same area of the HR diagram as the δ Scuti variables, should continue to be constrained by observations. In this context, it is necessary to extend the sample of studied pulsating Herbig Ae stars observed in high-resolution spectroscopy. The aim of this paper is to contribute to the systematic spectroscopic investigation of the PMS instability strip. We choose as targets the three Herbig stars V1247 Ori, HD35929 and HD190073. Our data were collected during three nights from 10 to 12 November 2008 with the HARPS spectrograph. V1247 Ori and HD35929 are known pulsating herbig stars, both having one photometrically detected frequency with timescale typical of δ Scuti pulsations. Till now, no search for stellar pulsations in HD190073 has been published. In this article, we search for stellar pulsations, and especially very faint signatures of non-radial pulsations, in the equivalent photospheric (LSD) profile time-series of our targets. Temporal variations of the LSD-profile central depth, if present, was studied with the time-series analysis tools Period04 and SigSpec. In case of oscillation detection, we then performed a 2D Fourier analysis of the entire profile in order to identify the modes corresponding to the dominant frequencies. The pulsating nature of V1247 Ori and HD35929 was confirmed by our results. V1247 Ori: frequencies of 18.99±1d−1 and 11.26±1d−1 were detected, corresponding to modes of degree ℓ = 3 to 5 and ℓ = 0 or 1, respectively. HD35929: a frequency of 5.75±1.28d−1 was detected, corresponding to a mode of degre ℓ = 6 or 7. No pulsation signatures were found in the LSD-profile time-series of HD190073. [less ▲]

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See detailThe rapid rotation and complex magnetic field geometry of Vega
Petit, Pascal; Lignières, F.; Wade, G. A. et al

in Astronomy and Astrophysics (2010), 523

Context. The recent discovery of a weak surface magnetic field on the normal intermediate-mass star Vega raises the question of the origin of this magnetism in a class of stars that was not previously ... [more ▼]

Context. The recent discovery of a weak surface magnetic field on the normal intermediate-mass star Vega raises the question of the origin of this magnetism in a class of stars that was not previously known to host detectable magnetic fields. <br />Aims: We aim to confirm the field detection reported by Lignières et al. (2009, A&A, 500, L41) and provide additional observational constraints about the field characteristics, by modelling the large-scale magnetic geometry of the star and by investigating a possible seasonal variability of the reconstructed field topology. <br />Methods: We analyse a total of 799 high-resolution circularly-polarized spectra collected with the NARVAL and ESPaDOnS spectropolarimeters during 2008 and 2009. Using about 1100 spectral lines, we employ a cross-correlation procedure to compute, from each spectrum, a mean polarized line profile with a signal-to-noise ratio of about 20 000. The technique of Zeeman-Doppler Imaging is then used to determine the rotation period of the star and reconstruct the large-scale magnetic geometry of Vega at two different epochs. <br />Results: We confirm the detection of circularly polarized signatures in the mean line profiles. The signal shows up in four independent data sets acquired with both NARVAL and ESPaDOnS. The amplitude of the polarized signatures is larger when spectral lines of higher magnetic sensitivity are selected for the analysis, as expected for a signal of magnetic origin. The short-term evolution of polarized signatures is consistent with a rotational period of 0.732 ± 0.008 d. The reconstruction of the magnetic topology unveils a magnetic region of radial field orientation, closely concentrated around the rotation pole. This polar feature is accompanied by a small number of magnetic patches at lower latitudes. No significant variability in the field structure is observed over a time span of one year. <br />Conclusions: The repeated observational evidence that Vega possesses a weak photospheric magnetic field strongly suggests that a previously unknown type of magnetic stars exists in the intermediate-mass domain. Vega may well be the first confirmed member of a much larger, as yet unexplored, class of weakly-magnetic stars now investigatable with the current generation of stellar spectropolarimeters. [less ▲]

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See detailAsteroseismology and mode driving of the Herbig Ae star HD 104237
Dupret, Marc-Antoine ULg; Théado, S.; Böhm, T. et al

in Communications in Asteroseismology (2007), 150

Eight pulsation frequencies were detected in the Herbig Ae star HD 104237 during two observational campaigns in 1999 -- 2000 (Böhm et al. 2004). Moreover, Böhm et al. (in preparation) detected recently in ... [more ▼]

Eight pulsation frequencies were detected in the Herbig Ae star HD 104237 during two observational campaigns in 1999 -- 2000 (Böhm et al. 2004). Moreover, Böhm et al. (in preparation) detected recently in their data two independent signatures of a signal at 95 hr that corresponds probably to rotational modulation. We present here a seismic study of this Pre-Main Sequence star based on these observations. Different possible interpretations of the pulsation spectrum are considered. The driving of the pulsation modes is not explained by standard models, the observed frequencies being too high for delta Scuti-type pulsations. We consider the effect of He accumulation in its partial ionization zones as a possible explanation for this driving. [less ▲]

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See detailThe Seismology Programme of CoRoT
Michel, Eric; Baglin, A.; Auvergne, M. et al

in Proceedings of "The CoRoT Mission Pre-Launch Status - Stellar Seismology and Planet Finding (2006, November 01)

We introduce the main lines and specificities of the CoRoT Seismology Core Programme. The development and consolidation of this programme has been made in the framework of the CoRoT Seismology Working ... [more ▼]

We introduce the main lines and specificities of the CoRoT Seismology Core Programme. The development and consolidation of this programme has been made in the framework of the CoRoT Seismology Working Group. With a few illustrative examples, we show how CoRoT data will help to address various problems associated with present open questions of stellar structure and evolution. [less ▲]

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See detailSeismic study of the Herbig Ae star HD 104237
Dupret, Marc-Antoine ULg; Böhm, T.; Goupil, Marie-José et al

in Communications in Asteroseismology (2006), 147

HD 104237 is the brightest Herbig Ae star, and as such a pre-main sequence (PMS) star. It is also a spectroscopic binary with determined orbital parameters. It was observed in 1999-2000 at SAAO and Mt ... [more ▼]

HD 104237 is the brightest Herbig Ae star, and as such a pre-main sequence (PMS) star. It is also a spectroscopic binary with determined orbital parameters. It was observed in 1999-2000 at SAAO and Mt Stromolo and 1888 Echelle spectra were obtained. From these observations, 8 pulsation frequencies were detected among which 5 with very high confidence (Böhm et al. 2004). We present here a preliminary seismic study based on these observations. We also consider the problem of the excitation of the observed modes and show, as an important result of our study, that HD 104237 is not a delta Sct type pulsator. [less ▲]

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See detailSeismology and rotation of the Herbig Ae star HD 104237 .
Böhm, T.; Dupret, Marc-Antoine ULg; Aynedjian, H.

in Memorie della Societa Astronomica Italiana (2006), 77

HD 104237 is the first pulsating Herbig Ae star for which very recently a significant number of pulsation frequencies has been detected by means of high-resolution spectroscopy. The high quality radial ... [more ▼]

HD 104237 is the first pulsating Herbig Ae star for which very recently a significant number of pulsation frequencies has been detected by means of high-resolution spectroscopy. The high quality radial velocity curve based on 1888 individual echelle spectra obtained in 42 nights in 1999 and 2000 revealed for the first time by spectroscopic means multiperiodic oscillations in a pre-main sequence star: a total of 8 frequencies have been detected so far, 5 amongst them were detected at a very high confidence level Böhm et al. \cite{pulsation}. This result encouraged us to develop asterosismological models for such young pre-main sequence pulsator (Dupret et al. \cite{dupret}), but the dramatic lack of a precise knowledge of the fundamental stellar parameters appear still to be critical. A summary of the main results of the pulsation study are presented and first indications for a stellar rotational modulation are exhibited. [less ▲]

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