References of "Mazumdar, A"
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See detailA multisite photometric study of two unusual β Cep stars: the magnetic V2052 Oph and the massive rapid rotator V986 Oph
Handler, G.; Shobbrook, R. R.; Uytterhoeven, K. et al

in Monthly Notices of the Royal Astronomical Society (2012), 424

We report a multisite photometric campaign for the β Cep stars V2052 Oph and V986 Oph. 670 h of high-quality differential photoelectric Strömgren, Johnson and Geneva time-series photometry was obtained ... [more ▼]

We report a multisite photometric campaign for the β Cep stars V2052 Oph and V986 Oph. 670 h of high-quality differential photoelectric Strömgren, Johnson and Geneva time-series photometry was obtained with eight telescopes on five continents during 182 nights. Frequency analyses of the V2052 Oph data enabled the detection of three pulsation frequencies, the first harmonic of the strongest signal, and the rotation frequency with its first harmonic. Pulsational mode identification from analysing the colour amplitude ratios confirms the dominant mode as being radial, whereas the other two oscillations are most likely l = 4. Combining seismic constraints on the inclination of the rotation axis with published magnetic field analyses we conclude that the radial mode must be the fundamental mode. The rotational light modulation is in phase with published spectroscopic variability, and consistent with an oblique rotator for which both magnetic poles pass through the line of sight. The inclination of the rotation axis is 54° < i < 58° and the magnetic obliquity 58° < β < 66°. The possibility that V2052 Oph has a magnetically confined wind is discussed. The photometric amplitudes of the single oscillation of V986 Oph are most consistent with an l = 3 mode, but this identification is uncertain. Additional intrinsic, apparently temporally incoherent light variations of V986 Oph are reported. Different interpretations thereof cannot be distinguished at this point, but this kind of variability appears to be present in many OB stars. The prospects of obtaining asteroseismic information for more rapidly rotating β Cep stars, which appear to prefer modes of higher l, are briefly discussed. [less ▲]

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See detailLong term photometric monitoring with the Mercator telescope. Frequencies and mode identification of variable O-B stars
De Cat, P.; Briquet, Maryline ULg; Aerts, C. et al

in Astronomy and Astrophysics (2007), 463

Aims. We selected a large sample of O-B stars that were considered as (candidate) slowly pulsating B, beta Cep, and Maia stars after the analysis of their hipparcos data. We analysed our new seven ... [more ▼]

Aims. We selected a large sample of O-B stars that were considered as (candidate) slowly pulsating B, beta Cep, and Maia stars after the analysis of their hipparcos data. We analysed our new seven passband geneva data collected for these stars during the first three years of scientific operations of the mercator telescope. We performed a frequency analysis for 28 targets with more than 50 high-quality measurements to improve their variability classification. For the pulsating stars, we tried both to identify the modes and to search for rotationally split modes. Methods: We searched for frequencies in all the geneva passbands and colours by using two independent frequency analysis methods and we applied a 3.6 S/N-level criterion to locate the significant peaks in the periodograms. The modes were identified by applying the method of photometric amplitudes for which we calculated a large, homogeneous grid of equilibrium models to perform a pulsational stability analysis. When both the radius and the projected rotational velocity of an object are known, we determined a lower limit for the rotation frequency to estimate the expected frequency spacings in rotationally split pulsation modes. Results: We detected 61 frequencies, among which 33 are new. We classified 21 objects as pulsating variables (7 new confirmed pulsating stars, including 2 hybrid beta Cep/SPB stars), 6 as non-pulsating variables (binaries or spotted stars), and 1 as photometrically constant. All the Maia candidates were reclassified into other variability classes. We performed mode identification for the pulsating variables for the first time. The most probable l value is 0, 1, 2, and 4 for 1, 31, 9, and 5 modes, respectively, including only 4 unambiguous identifications. For 7 stars we cannot rule out that some of the observed frequencies belong to the same rotationally split mode. For 4 targets we may begin to resolve close frequency multiplets. Based on observations collected with the p7 photometer attached to the Flemish 1.2-m mercator telescope situated at the Roque de los Muchachos observatory on La Palma (Spain). Section [see full textsee full text], including Figs. is only available in electronic form at http://www.aanda.org, and Tables 2 and 3 are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/463/243 [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 detailAn asteroseismic study of the β Cephei star β Canis Majoris
Mazumdar, A.; Briquet, Maryline ULg; Desmet, M. et al

in Astronomy and Astrophysics (2006), 459

Aims.We present the results of a detailed analysis of 452 ground-based, high-resolution high S/N spectroscopic measurements spread over 4.5 years for β Canis Majoris with the aim of determining the ... [more ▼]

Aims.We present the results of a detailed analysis of 452 ground-based, high-resolution high S/N spectroscopic measurements spread over 4.5 years for β Canis Majoris with the aim of determining the pulsational characteristics of this star, and then using them to derive seismic constraints on the stellar parameters.<BR /> Methods: .We determined pulsation frequencies in the Si III 4553 Å line with Fourier methods. We identified the m-value of the modes by taking the photometric identifications of the degrees ℓ into account. To this end we used the moment method together with the amplitude and phase variations across the line profile. The frequencies of the identified modes were used for a seismic interpretation of the structure of the star.<BR /> Results: .We confirm the presence of the three pulsation frequencies already detected in previous photometric datasets: f[SUB]1[/SUB] = 3.9793~c d[SUP]-1[/SUP] (46.057~μHz), f[SUB]2[/SUB] = 3.9995~c d[SUP]-1[/SUP] (46.291~μHz), and f[SUB]3[/SUB] = 4.1832~c d[SUP]-1[/SUP] (48.417~μHz). For the two modes with the highest amplitudes, we unambiguously identify (ℓ_1,m_1) = (2,2) and (ℓ_2,m_2) = (0,0). We cannot conclude anything for the third mode identification, except that m[SUB]3[/SUB] > 0. We also deduce an equatorial rotational velocity of 31 ± 5~km s[SUP]-1[/SUP] for the star. We show that the mode f[SUB]1[/SUB] must be close to an avoided crossing. Constraints on the mass (13.5 ± 0.5~μHz), age (12.4 ± 0.7 Myr), and core overshoot (0.20 ± 0.05 H_P) of β CMa are obtained from seismic modelling using f[SUB]1[/SUB] and f_2.<BR /> [less ▲]

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See detailAn asteroseismic study of the beta Cephei star beta Canis Majoris
Desmet, M.; Briquet, Maryline ULg; Mazumdar, A. et al

in Communications in Asteroseismology (2006), 147

We present a spectroscopic study of the beta Cephei star beta Canis Majoris. Hundreds of high-resolution spectra were gathered during 4.5 years and the Si III line profiles centered on 4560 A were ... [more ▼]

We present a spectroscopic study of the beta Cephei star beta Canis Majoris. Hundreds of high-resolution spectra were gathered during 4.5 years and the Si III line profiles centered on 4560 A were subjected to a detailed line profile analysis. We searched for oscillation frequencies in different line diagnostics, compared them with those known from photometric studies and concluded the presence of three frequencies in our dataset: f_1 = 3.97933 c/d, f_2 = 3.99959 c/d and f_3= 4.1832 c/d, which were already found earlier from photometric data. By means of the moment method and from amplitude and phase variations across the profiles we could identify two of the modes as (l_1,m_1)=(2,2) and (l_2,m_2)=(0,0$. We present our first results of modelling based on the oscillation frequencies and place constraints on the mass, age and core overshooting of this massive evolved beta Cephei star. [less ▲]

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