275 research outputs found
Discovery of Rapid oscillations in HD 218994
No full textAsteroseismology has the potential to provide new insights into the physics of stellar interiors. Among the most promising objects that can be studied through this technique are the rapidly oscillating Ap (roAp) stars. These pulsate in high-overtone, low-degree, nonradial p-modes, with periods in the range 6-21 min. Our previous study (Hubrig et al., 2000) discussed the relationship between the roAp stars and the non-oscillating Ap (noAp) stars and concluded that the noAp stars are, in general, slightly more evolved than the roAp stars. The Ap Sr star HD 218994 was checked photometrically for the presence of rapid oscillations in the Cape Survey, but no oscillations have been detected by Martinez & Kurtz. This star was previously included in the sample of non-pulsating binary Ap stars studied by Hubrig et al. (2000). We have been granted one hour of UVES high time resolution observations of this star at ESO VLT on Cierro Paranal on November 15, 2006 and were able to obtain 15 spectra with exposure times of 3 min and a sampling of 3.7 min, taking into account the CCD readout time. To search for pulsational line variability, we calculated the average spectrum of the observed 15 spectra and subtracted it from the original spectra. In Fig. 1 we present the behaviour of the spectral profile of the Nd III line at {lambda} 6327 and its standard deviations. Similar variations were also found for the Pr III lines at {lambda} 6053 and {lambda} 6090. It was already shown in numerous studies that rare elements have higher amplitudes in roAp stars compared to lines of Fe-peak elements (e.g. Kurtz, Elkin & Mathys 2005). We also note that the mean RV for different elements is different, indicating the presence of chemical inhomogeneities on the stellar surface. Our analysis of RV variations of the Nd III line indicates two pulsation periods: one period of 5.1 min with an amplitude of 516 m/s and another one of 13.9 min and an amplitude of 497 m/s. It is very likely that one of these peaks is an alias. The amplitude spectrum of the radial velocity variations is presented in Fig. 2. We note that a longer time series with better temporal resolution is needed for a careful identification of the principal frequency and a search for the presence of other pulsation frequencies. To confirm the detected spectroscopic variation period, we searched for a periodicity in the photometric data using Hipparcos and ASAS photometric databases. Indeed, also the photometric data show a sinusoidal variation with a period identical to the spectroscopic period, P=5.1 min, and an amplitude of 0.005 mag. In Fig. 3 we present both the RV variations of the Nd III line and the ASAS light curve. The star HD 218994 becomes now the 36th star known to be a roAp star.Fil: Gonzalez, Jorge Federico. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Complejo Astronómico "El Leoncito". Universidad Nacional de Córdoba. Complejo Astronómico "El Leoncito". Universidad Nacional de la Plata. Complejo Astronómico "El Leoncito". Universidad Nacional de San Juan. Complejo Astronómico "El Leoncito"; ArgentinaFil: Hubrig, S.. European Southern Observatory; EspañaFil: Savanov, I.. College Hill; Irland
Discovery of Rapid oscillations in HD 218994
No full textAsteroseismology has the potential to provide new insights into the physics of stellar interiors. Among the most promising objects that can be studied through this technique are the rapidly oscillating Ap (roAp) stars. These pulsate in high-overtone, low-degree, nonradial p-modes, with periods in the range 6-21 min. Our previous study (Hubrig et al., 2000) discussed the relationship between the roAp stars and the non-oscillating Ap (noAp) stars and concluded that the noAp stars are, in general, slightly more evolved than the roAp stars. The Ap Sr star HD 218994 was checked photometrically for the presence of rapid oscillations in the Cape Survey, but no oscillations have been detected by Martinez & Kurtz. This star was previously included in the sample of non-pulsating binary Ap stars studied by Hubrig et al. (2000). We have been granted one hour of UVES high time resolution observations of this star at ESO VLT on Cierro Paranal on November 15, 2006 and were able to obtain 15 spectra with exposure times of 3 min and a sampling of 3.7 min, taking into account the CCD readout time. To search for pulsational line variability, we calculated the average spectrum of the observed 15 spectra and subtracted it from the original spectra. In Fig. 1 we present the behaviour of the spectral profile of the Nd III line at {lambda} 6327 and its standard deviations. Similar variations were also found for the Pr III lines at {lambda} 6053 and {lambda} 6090. It was already shown in numerous studies that rare elements have higher amplitudes in roAp stars compared to lines of Fe-peak elements (e.g. Kurtz, Elkin & Mathys 2005). We also note that the mean RV for different elements is different, indicating the presence of chemical inhomogeneities on the stellar surface. Our analysis of RV variations of the Nd III line indicates two pulsation periods: one period of 5.1 min with an amplitude of 516 m/s and another one of 13.9 min and an amplitude of 497 m/s. It is very likely that one of these peaks is an alias. The amplitude spectrum of the radial velocity variations is presented in Fig. 2. We note that a longer time series with better temporal resolution is needed for a careful identification of the principal frequency and a search for the presence of other pulsation frequencies. To confirm the detected spectroscopic variation period, we searched for a periodicity in the photometric data using Hipparcos and ASAS photometric databases. Indeed, also the photometric data show a sinusoidal variation with a period identical to the spectroscopic period, P=5.1 min, and an amplitude of 0.005 mag. In Fig. 3 we present both the RV variations of the Nd III line and the ASAS light curve. The star HD 218994 becomes now the 36th star known to be a roAp star.Fil: Gonzalez, Jorge Federico. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Complejo Astronómico "El Leoncito". Universidad Nacional de Córdoba. Complejo Astronómico "El Leoncito". Universidad Nacional de la Plata. Complejo Astronómico "El Leoncito". Universidad Nacional de San Juan. Complejo Astronómico "El Leoncito"; ArgentinaFil: Hubrig, S.. European Southern Observatory; EspañaFil: Savanov, I.. College Hill; Irland
Lanthanides and other spectral oddities in a Centauri: Ce III, Nd III, KrII, and broad absorption features
No full textContext. There is considerable interest in the helium variable a Cen as a bridge between helium-weak and helium-strong CP stars.
Aims. We investigate Ce iii and other possible lanthanides in the spectrum the of hottest chemically peculiar (CP) star in which these elements have been found. A Kr ii line appears within a broad absorption which we suggest may be due to a high-level transition in C ii.
Methods. Wavelengths and equivalent widths are measured on high-resolution UVES spectra, analyzed, and their phase-variations investigated.
Results. New, robust identifications of Ce iii and Kr ii are demonstrated. Nd iii is likely present. A broad absorption near λ4619 is present at all phases of a Cen, and in some other early B stars.
Conclusions. The presence of lanthanides in a Cen strengthens the view that this star is a significant link between the cooler CP stars and the hotter helium-peculiar stars. Broad absorptions in a Cen are not well explained.Fil: Cowley, C. R.. University Of Michigan; Estados UnidosFil: Hubrig, S.. AIP; AlemaniaFil: Gonzalez, Jorge Federico. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico San Juan. Instituto de Ciencias Astronomicas de la Tierra y del Espacio; Argentin
Binarity Versus Magnetic Fields in Upper Main-sequence Stars
No full textWe review the status of the work on the detection, possible origin, and modelling of magnetic fields in binary systems with intermediate- and higher-mass primaries at different evolutionary stages. This review also includes interesting findings on a few exotic systems.Fil: Hubrig, S.. Leibniz-Institut für Astrophysik Potsdam; AlemaniaFil: Schöller, M.. European Southern Observatory; AlemaniaFil: Ilyin, I.. Leibniz-Institut für Astrophysik Potsdam; AlemaniaFil: Gonzalez, Jorge Federico. Consejo Nacional de Investigaciones CientiÂficas y Tecnicas. Centro Cientifico Tecnologico San Juan. Instituto de Ciencias Astronomicas de la Tierra y del Espacio; ArgentinaFil: Mikulásek, Z.. Masaryk University. Department of Theoretical Physics and Astrophysics; República Chec
HD149277: A rare short-period SB2 system with a subsynchronously rotating magnetic He-rich primary
No full textHD149277 is a rare SB2 system with a slowly rotating magnetic He-rich primary with Prot = 25.4 d. The CFHT/ESPaDOnS archive spectra revealed Porb = 11.5192 ± 0.0005 d indicating strong subsynchronous rotation of the primary component. Such a strong subsynchronous rotation was not detected in any other SB2 system with a magnetic chemically peculiar component. Our inspection of the spectra revealed the presence of resolved Zeeman split spectral lines allowing us to determine the variability of the mean magnetic field modulus over the rotation period. The maximum of the magnetic field modulus coincides roughly with the positive extremum of the longitudinal field, whereas the minimum of the modulus with the negative extremum of the longitudinal field. No evidence for a longitudinal magnetic field was seen in the circularly polarized spectra of the secondary component. Using archival data from the ASAS3 survey, we find in the frequency spectrum only one significant peak, corresponding to the period Pphot = 25.390 ± 0.014 d. This value is in good agreements with the previous determination of the rotation period, Prot =25.380±0.007 d, which was based on longitudinal magnetic field measurements.Fil: Gonzalez, Jorge Federico. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Instituto de Ciencias Astronómicas, de la Tierra y del Espacio. Universidad Nacional de San Juan. Instituto de Ciencias Astronómicas, de la Tierra y del Espacio; ArgentinaFil: Hubrig, S.. Leibniz Institute For Astrophysics Potsdam; AlemaniaFil: Järvinen, S. P.. Leibniz Institute For Astrophysics Potsdam; AlemaniaFil: Schöller, M.. European Southern Observatory; Alemani
HgMn Stars: Cornerstones for our Understanding of Late B-type Multiple Star Formation
No full textThe most distinctive feature of HgMn stars is the extreme overabundance of heavy elements in their atmospheres. Furthermore, they show chemical horizontal and vertical inhomogeneities and kG mean quadratic magnetic fields. The topology of these magnetic fields should be rather complex, as we measure only weak mean longitudinal magnetic fields. The connection between these features and their membership in binary and multiple systems is supported by our observations during the last decade. The most important result achieved in our studies of a large sample of late B-type primaries in spectroscopic binaries and visual multiples is the finding that the vast majority of slowly rotating late B-type stars formed in binary systems with v sin i < 70 km s^{-1} and orbital periods between 3 and 20 days become HgMn stars.Fil: Schöller, M.. European Southern Observatory; AlemaniaFil: Hubrig, S.. Leibniz-Institut für Astrophysik Potsdam; AlemaniaFil: Correia, S.. Leibniz-Institut für Astrophysik Potsdam; AlemaniaFil: Ilyin, I.. Leibniz-Institut für Astrophysik Potsdam; AlemaniaFil: Gonzalez, Jorge Federico. Consejo Nacional de Investigaciones CientiÂficas y Tecnicas. Centro Cientifico Tecnologico San Juan. Instituto de Ciencias Astronomicas de la Tierra y del Espacio; Argentin
Discovery of pulsational line profile variations in the δ Scuti star HD 21190 and in the Ap Sr star HD 218994★
No full textAsteroseismology has the potential to provide new insights into the physics of stellar interiors. We have obtained Ultraviolet and Visual Echelle Spectrograph high time-resolution observations of the δ Scuti star HD21190 and of the Ap Sr star HD218994 to search for pulsational line profile variations. We report the discovery of a new roAp star, HD218994, with a pulsation period of 14.2min. This is one of the most evolved roAp stars. No rapid pulsations have been found in the spectra of the cool Ap star - δ Scuti star HD21190. However, we detect with unprecedented clarity for a δScuti star moving peaks in the cores of spectral lines that indicate the presence of high-degree non-radial pulsations in this star.Fil: Gonzalez, Jorge Federico. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Complejo Astronómico "El Leoncito". Universidad Nacional de Córdoba. Complejo Astronómico "El Leoncito". Universidad Nacional de la Plata. Complejo Astronómico "El Leoncito". Universidad Nacional de San Juan. Complejo Astronómico "El Leoncito"; ArgentinaFil: Hubrig, S.. European Southern Observatory Chile; ChileFil: Kurtz, D. W.. University of Central Lancashire; Estados UnidosFil: Elkin, V.. University of Central Lancashire; Estados UnidosFil: Savanov, I.. College Hill; Irland
The magnetic field of the stripped primary in the upsilon Sgr system, a member of the rare class of hydrogen-deficient binaries
No full textWe present the results of high-resolution spectropolarimetric observations of
the optically dominant component in the rare hydrogen-deficient binary system
upsilon Sgr. Only a small number of such systems in a very late phase of helium
shell burning are currently known. The mass transfer from the donor star in
binary systems usually leads to the stripping of its hydrogen envelope.
Consequently, since the mass of the secondary increases, it appears
rejuvenated. Using a few ESO FORS1 low-resolution spectropolarimetric
observations of this system, Hubrig et al. announced in 2009 the presence of a
magnetic field of the order of -70 - -80G. Here we report on more recent
high-resolution ESO HARPS spectropolarimetric observations showing that the
primary in upsilon Sgr is a spectrum variable star and possesses a weak
magnetic field of the order of a few tens of Gauss. The detection of a magnetic
field in this rare hydrogen-deficient binary is of particular interest, as such
systems are frequently discussed as probable progenitors of core-collapse
supernovae and gravitational-wave sources. Future magnetic studies of such
systems will be worthwhile to gain deeper insights into the role of magnetic
fields in the evolution of massive stars in binary systems.Comment: 7 pages, 2 tables, 2 figures, accepted for publication in Ap
HD 161701, a chemically peculiar binary with a HgMn primary and an Ap secondary
No full textIn recent years, HgMn stars have attracted attention after in several of them surface chemical spots of different elements were discovered, whose origin and possible connection with binarity and magnetic fields is not clear yet. Aims. We perform a complete study of the HgMn binary HD 161701, including the determination of physical parameters and photospheric chemical abundances.Fil: Gonzalez, Jorge Federico. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico - CONICET - San Juan. Instituto de Ciencias Astronómicas de la Tierra y del Espacio; Argentina;Fil: Saffe, Carlos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico - CONICET - San Juan. Instituto de Ciencias Astronómicas de la Tierra y del Espacio; Argentina;Fil: Castelli, F.. Istituto Nazionale di Astrofisica. Osservatorio Astronomico di Trieste; Italia;Fil: Hubrig, S.. Leibniz Institute for Astrophysics Potsdam; Alemania;Fil: Ilyin, I.. Leibniz Institute for Astrophysics Potsdam, Alemania;Fil: Schöller, M.. European Southern Observatory, Alemania;Fil: Carroll, T. A.. Leibniz Institute for Astrophysics Potsdam, Alemania;Fil: Leone, F.. Università di Catania. Dipartimento di Fisica e Astronomia. Sezione Astrofisica; Italia;Fil: Giarrusso, M.. Università di Catania. Dipartimento di Fisica e Astronomia. Sezione Astrofisica; Italia; Osservatorio Astrofisico di Catania; Italia
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