References of "Lehmann, H"
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See detailExtensive study of HD 25558, a long-period double-lined binary with two SPB components
Sódor, Á.; De Cat, P.; Wright, D. J. et al

in Monthly Notices of the Royal Astronomical Society (2014), 438(4), 3535-3556

We carried out an extensive observational study of the Slowly Pulsating B (SPB) star, HD 25558. The ~2000 spectra obtained at different observatories, the ground-based and MOST satellite light curves ... [more ▼]

We carried out an extensive observational study of the Slowly Pulsating B (SPB) star, HD 25558. The ~2000 spectra obtained at different observatories, the ground-based and MOST satellite light curves revealed that this object is a double-lined spectroscopic binary with an orbital period of about 9 years. The observations do not allow the inference of an orbital solution. We determined the physical parameters of the components, and found that both lie within the SPB instability strip. Accordingly, both show line-profile variations due to stellar pulsations. Eleven independent frequencies were identified in the data. All the frequencies were attributed to one of the two components based on Pixel-by-pixel variability analysis of the line profiles. Spectroscopic and photometric mode identification was also performed for the frequencies of both stars. These results suggest that the inclination and rotation of the two components are rather different. The primary is a slow rotator with ~6 d period, seen at ~60 deg inclination, while the secondary rotates fast with ~1.2 d period, and is seen at ~20 inclination. Spectropolarimetric measurements revealed that the secondary component has a magnetic field with at least a few hundred Gauss strength, while no magnetic field can be detected in the primary. [less ▲]

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See detailA search for pulsations in the HgMn star HD 45975 with CoRoT photometry and ground-based spectroscopy
Morel, Thierry ULg; Briquet, Maryline ULg; Auvergne, M. et al

in Astronomy and Astrophysics (2014), 561

The existence of pulsations in HgMn stars is still being debated. To provide the first unambiguous observational detection of pulsations in this class of chemically peculiar objects, the bright star HD ... [more ▼]

The existence of pulsations in HgMn stars is still being debated. To provide the first unambiguous observational detection of pulsations in this class of chemically peculiar objects, the bright star HD 45975 was monitored for nearly two months by the CoRoT satellite. Independent analyses of the light curve provide evidence of monoperiodic variations with a frequency of 0.7572 d[SUP]-1[/SUP] and a peak-to-peak amplitude of ~2800 ppm. Multisite, ground-based spectroscopic observations overlapping the CoRoT observations show the star to be a long-period, single-lined binary. Furthermore, with the notable exception of mercury, they reveal the same periodicity as in photometry in the line moments of chemical species exhibiting strong overabundances (e.g., Mn and Y). In contrast, lines of other elements do not show significant variations. As found in otherHgMn stars, the pattern of variability consists in an absorption bump moving redwards across the line profiles. We argue that the photometric and spectroscopic changes are more consistent with an interpretation in terms of rotational modulation of spots at the stellar surface. In this framework, the existence of pulsations producing photometric variations above the ~50 ppm level is unlikely in HD 45975. This provides strong constraints on the excitation/damping of pulsation modes in this HgMn star. The CoRoT space mission was developed and is operated by the French space agency CNES, with participation of ESA's RSSD and Science Programmes, Austria, Belgium, Brazil, Germany, and Spain. This work is based on observations collected at La Silla and Paranal Observatories, ESO (Chile), with the HARPS and UVES spectrographs at the 3.6-m and very large telescopes, under programmes LP185.D-0056 and 287.D-5066. It is also based on observations made with the Mercator Telescope, operated on the island of La Palma by the Flemish Community, at the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias. Based on observations obtained with the HERMES spectrograph, which is supported by the Fund for Scientific Research of Flanders (FWO), Belgium, the Research Council of K.U. Leuven, Belgium, the Fonds National de la Recherche Scientifique (FNRS), Belgium, the Royal Observatory of Belgium, the Observatoire de Genève, Switzerland, and the Thüringer Landessternwarte Tautenburg, Germany. [less ▲]

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See detailMultisite spectroscopic seismic study of the β Cep star V2052 Ophiuchi: inhibition of mixing by its magnetic field
Briquet, Maryline ULg; Neiner, C.; Aerts, C. et al

in Monthly Notices of the Royal Astronomical Society (2012), 427

We used extensive ground-based multisite and archival spectroscopy to derive observational constraints for a seismic modelling of the magnetic β Cep star V2052 Ophiuchi. The line-profile variability is ... [more ▼]

We used extensive ground-based multisite and archival spectroscopy to derive observational constraints for a seismic modelling of the magnetic β Cep star V2052 Ophiuchi. The line-profile variability is dominated by a radial mode (f1 = 7.148 46 d-1) and by rotational modulation (P_rot = 3.638 833 d). Two non-radial low-amplitude modes (f2 = 7.756 03 d-1 and f3 = 6.823 08 d-1) are also detected. The four periodicities that we found are the same as the ones discovered from a companion multisite photometric campaign and known in the literature. Using the photometric constraints on the degrees ℓ of the pulsation modes, we show that both f_2 and f_3 are prograde modes with (ℓ, m) = (4, 2) or (4, 3). These results allowed us to deduce ranges for the mass (M ∈ [8.2, 9.6] M_sun) and central hydrogen abundance (X_c ∈ [0.25, 0.32]) of V2052 Oph, to identify the radial orders n1 = 1, n2 = -3 and n3 = -2, and to derive an equatorial rotation velocity v_eq ∈ [71, 75] km s-1. The model parameters are in full agreement with the effective temperature and surface gravity deduced from spectroscopy. Only models with no or mild core overshooting (α_ov ∈ [0, 0.15] local pressure scale heights) can account for the observed properties. Such a low overshooting is opposite to our previous modelling results for the non-magnetic β Cep star θ Oph having very similar parameters, except for a slower surface rotation rate. We discuss whether this result can be explained by the presence of a magnetic field in V2052 Oph that inhibits mixing in its interior. [less ▲]

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See detailKepler observations of the variability in B-type stars
Balona, L. A.; Pigulski, A.; Cat, P De et al

in Monthly Notices of the Royal Astronomical Society (2011), 413

The analysis of the light curves of 48 B-type stars observed by Kepler is presented. Among these are 15 pulsating stars, all of which show low frequencies, characteristic of slowly pulsating B (SPB) stars ... [more ▼]

The analysis of the light curves of 48 B-type stars observed by Kepler is presented. Among these are 15 pulsating stars, all of which show low frequencies, characteristic of slowly pulsating B (SPB) stars. Seven of these stars also show a few weak, isolated high frequencies and they could be considered as SPB/β Cephei (β Cep) hybrids. In all cases, the frequency spectra are quite different from what is seen from ground-based observations. We suggest that this is because most of the low frequencies are modes of high degree which are predicted to be unstable in models of mid-B stars. We find that there are non-pulsating stars within the β Cep and SPB instability strips. Apart from the pulsating stars, we can identify stars with frequency groupings similar to what is seen in Be stars but which are not Be stars. The origin of the groupings is not clear, but may be related to rotation. We find periodic variations in other stars which we attribute to proximity effects in binary systems or possibly rotational modulation. We find no evidence for pulsating stars between the cool edge of the SPB and the hot edge of the δ Sct instability strips. None of the stars shows the broad features which can be attributed to stochastically excited modes as recently proposed. Among our sample of B stars are two chemically peculiar stars, one of which is a HgMn star showing rotational modulation in the light curve. [less ▲]

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See detailSpectral analysis of Kepler SPB and β Cephei candidate stars
Lehmann, H.; Tkachenko, A.; Semaan, T. et al

in Astronomy and Astrophysics (2011), 526

Context. For asteroseismic modelling, analysis of the high-accuracy light curves delivered by the Kepler satellite mission needs support by ground-based, multi-colour and spectroscopic observations. <BR ... [more ▼]

Context. For asteroseismic modelling, analysis of the high-accuracy light curves delivered by the Kepler satellite mission needs support by ground-based, multi-colour and spectroscopic observations. <BR /> Aims: We determine the fundamental parameters of SPB and β Cep candidate stars observed by the Kepler satellite mission and estimate the expected types of non-radial pulsators. <BR /> Methods: We compared newly obtained high-resolution spectra with synthetic spectra computed on a grid of stellar parameters assuming LTE, and checked for NLTE effects for the hottest stars. For comparison, we determined T[SUB]eff[/SUB] independently from fitting the spectral energy distribution of the stars obtained from the available photometry. <BR /> Results: We determine T[SUB]eff[/SUB], log g, microturbulent velocity, v sin i, metallicity, and elemental abundance for 14 of the 16 candidate stars. Two stars are spectroscopic binaries. No significant influence of NLTE effects on the results could be found. For hot stars, we find systematic deviations in the determined effective temperatures from those given in the Kepler Input Catalogue. The deviations are confirmed by the results obtained from ground-based photometry. Five stars show reduced metallicity, two stars are He-strong, one is He-weak, and one is Si-strong. Two of the stars could be β Cep/SPB hybrid pulsators, four SPB pulsators, and five more stars are located close to the borders of the SPB instability region. Based on observations with the 2-m Alfred Jensch telescope at the Thüringer Landessternwarte (TLS) Tautenburg. [less ▲]

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See detailHybrid gamma Doradus-delta Scuti Pulsators: New Insights into the Physics of the Oscillations from Kepler Observations
Grigahcène, Ahmed; Antoci, V.; Balona, L. et al

in Astrophysical Journal (2010), 713

Observations of the pulsations of stars can be used to infer their interior structure and test theoretical models. The main-sequence γ Doradus (Dor) and δ Scuti (Sct) stars with masses 1.2-2.5 M [SUB ... [more ▼]

Observations of the pulsations of stars can be used to infer their interior structure and test theoretical models. The main-sequence γ Doradus (Dor) and δ Scuti (Sct) stars with masses 1.2-2.5 M [SUB]sun[/SUB] are particularly useful for these studies. The γ Dor stars pulsate in high-order g-modes with periods of order 1 day, driven by convective blocking at the base of their envelope convection zone. The δ Sct stars pulsate in low-order g- and p-modes with periods of order 2 hr, driven by the κ mechanism operating in the He II ionization zone. Theory predicts an overlap region in the Hertzsprung-Russell diagram between instability regions, where "hybrid" stars pulsating in both types of modes should exist. The two types of modes with properties governed by different portions of the stellar interior provide complementary model constraints. Among the known γ Dor and δ Sct stars, only four have been confirmed as hybrids. Now, analysis of combined Quarter 0 and Quarter 1 Kepler data for hundreds of variable stars shows that the frequency spectra are so rich that there are practically no pure δ Sct or γ Dor pulsators, i.e., essentially all of the stars show frequencies in both the δ Sct and the γ Dor frequency range. A new observational classification scheme is proposed that takes into account the amplitude as well as the frequency and is applied to categorize 234 stars as δ Sct, γ Dor, δ Sct/γ Dor or γ Dor/δ Sct hybrids. [less ▲]

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See detailKepler observations: Light shed on the hybrid γ Doradus - δ Scuti pulsation phenomenon
Grigahcène, A.; Uytterhoeven, K.; Antoci, V. et al

in Astronomische Nachrichten (2010), 331

Through the observational study of stellar pulsations, the internal structure of stars can be probed and theoretical models can be tested. The main sequence γ Doradus (Dor) and δ Scuti (Sct) stars with ... [more ▼]

Through the observational study of stellar pulsations, the internal structure of stars can be probed and theoretical models can be tested. The main sequence γ Doradus (Dor) and δ Scuti (Sct) stars with masses 1.2-2.5 M[SUB]ȯ[/SUB] are particularly interesting for asteroseismic study. The γ Dor stars pulsate in high-order gravity (g) modes, with pulsational periods of order of one day. The δ Sct stars, on the other hand, show low-order g and pressure (p) modes with periods of order of 2 hours. Theory predicts the existence of `hybrid' stars, i.e. stars pulsating in both types of modes, in an overlap region between the instability strips of γ Dor and δ Sct stars in the Hertzsprung-Russell diagram. Hybrid stars are particularly interesting as the two types of modes probe different regions of the stellar interior and hence provide complementary model constraints. Before the advent of Kepler, only a few hybrid stars had been confirmed. The {{Kepler}} satellite is providing a true revolution in the study of and search for hybrid stars. Analysis of the first 50 days of {{Kepler}} data of hundreds of γ Dor and δ Sct candidates reveals extremely rich frequency spectra, with most stars showing frequencies in both the δ Sct and γ Dor frequency range. As these results show that there are practically no pure δ Sct or γ Dor pulsators, a new observational classification scheme is proposed by \cite{Grig10}. We present their results and characterize 234 stars in terms of δ Sct, γ Dor, δ Sct/γ Dor or γ Dor/δ Sct hybrids. [less ▲]

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See detailAn asteroseismic study of the β Cephei star 12 Lacertae: multisite spectroscopic observations, mode identification and seismic modelling
Desmet, M.; Briquet, Maryline ULg; Thoul, Anne ULg et al

in Monthly Notices of the Royal Astronomical Society (2009), 396

We present the results of a spectroscopic multisite campaign for the β Cephei star 12 (DD) Lacertae. Our study is based on more than thousand high-resolution high S/N spectra gathered with eight different ... [more ▼]

We present the results of a spectroscopic multisite campaign for the β Cephei star 12 (DD) Lacertae. Our study is based on more than thousand high-resolution high S/N spectra gathered with eight different telescopes in a time span of 11 months. In addition, we make use of numerous archival spectroscopic measurements. We confirm 10 independent frequencies recently discovered from photometry, as well as harmonics and combination frequencies. In particular, the slowly pulsating B-stars (SPB)-like g-mode with frequency 0.3428d[SUP]-1[/SUP] reported before is detected in our spectroscopy. We identify the four main modes as (l[SUB]1[/SUB], m[SUB]1[/SUB]) = (1, 1), (l[SUB]2[/SUB], m[SUB]2[/SUB]) = (0, 0), (l[SUB]3[/SUB], m[SUB]3[/SUB]) = (1, 0) and (l[SUB]4[/SUB], m[SUB]4[/SUB]) = (2, 1) for f[SUB]1[/SUB] = 5.178964d[SUP]-1[/SUP], f[SUB]2[/SUB] = 5.334224d[SUP]-1[/SUP], f[SUB]3[/SUB] = 5.066316d[SUP]-1[/SUP] and f[SUB]4[/SUB] = 5.490133d[SUP]-1[/SUP], respectively. Our seismic modelling shows that f[SUB]2[/SUB] is likely the radial first overtone and that the core overshooting parameter α[SUB]ov[/SUB] is lower than 0.4 local pressure scale heights. [less ▲]

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See detailA spectroscopic study of the β Cephei star 12 (DD) Lacertae
Desmet, M.; Briquet, Maryline ULg; De Cat, P. et al

in Communications in Asteroseismology (2007), 150

We present first results of a spectroscopic multisite campaign for 12 (DD) Lacertae (hereinafter 12 Lac). This star is one of the best observed β Cephei stars. It has a large number of known oscillation ... [more ▼]

We present first results of a spectroscopic multisite campaign for 12 (DD) Lacertae (hereinafter 12 Lac). This star is one of the best observed β Cephei stars. It has a large number of known oscillation frequencies but a lack of identified m-values for its detected modes. In our data set we find seven independent frequencies together with combination frequencies. In addition, two of these modes are identified: one radial mode and one prograde dipole mode. [less ▲]

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See detailSeismic modelling of the beta Cep star EN (16) Lacertae
Thoul, Anne ULg; Aerts, C.; Dupret, Marc-Antoine ULg et al

in Astronomy and Astrophysics (2003), 406(1), 287-292

We perform seismic modelling of the massive beta Cep star EN Lacertae. The starting point of our analysis is the spectroscopic mode identification recently performed. To this, we add a new updated ... [more ▼]

We perform seismic modelling of the massive beta Cep star EN Lacertae. The starting point of our analysis is the spectroscopic mode identification recently performed. To this, we add a new updated photometric mode identification based upon a non-adiabatic description of the eigenfunctions in the outer atmosphere. Both mode identifications agree and this allows us to fine-tune the stellar parameters of EN Lacertae with unprecedented precision. This is done by producing a huge amount of stellar models with different parameters and selecting those that fulfill the frequency values and the mode identification. Our study is the first one of its kind in which a reconcilation between observed pulsational characteristics and theoretical models can be achieved at a level that allows accurate determination of the basic stellar parameters of a massive oscillator. We derive a mass of M=9.62+/- 0.11 M[SUB]sun[/SUB] and an age of 15.7 million years if we assume that convective overshooting does not occur. [less ▲]

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See detailSpectroscopic mode identification for the beta Cephei star EN (16) Lacertae
Aerts, C.; Lehmann, H.; Briquet, Maryline ULg et al

in Astronomy and Astrophysics (2003), 399

We perform for the first time spectroscopic mode identification in the eclipsing binary beta Cephei star EN (16) Lac. This mode identification is based upon a time series of 942 line profiles of the He I ... [more ▼]

We perform for the first time spectroscopic mode identification in the eclipsing binary beta Cephei star EN (16) Lac. This mode identification is based upon a time series of 942 line profiles of the He I lambda lambda 6678 Åline in its spectrum. All three known frequencies f[SUB]1[/SUB], f,SUB>2,/SUB>, f[SUB]3[/SUB] of the star are present in the line-profile variations, but we failed to find additional modes. Using different identification methods we find conclusive evidence for the radial nature of the main mode and for the l=2, m=0 identification of the mode with frequency f[SUB]2[/SUB]. A unique identification of the third mode is not possible from the spectra, but we do derive that l[SUB]3[/SUB]<3. Fits to the amplitude and phase variability of the modes imply a rotation frequency between 0.1 and 0.4 c d[SUP]-1[/SUP]. The star's rotation axis is not aligned with the orbital axis. Based on observations gathered with the coudé spectrograph attached to the 2.0 m reflector telescope at Tautenburg Observatory. [less ▲]

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See detailMode Identification and Seismic Modelling of the Cep Star EN(16)Lac
Aerts, C.; Lehmann, H.; Scuflaire, Richard ULg et al

in Asteroseismology Across the HR Diagram (2003)

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