Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/643/A110
- Title:
- beta Cas BRITE and SMEI light curves
- Short Name:
- J/A+A/643/A110
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- F type stars are characterised by several physical processes such as different pulsation mechanisms, rotation, convection, diffusion, and magnetic fields. The rapidly rotating delta Scuti star beta Cas can be considered as a benchmark star to study the interaction of several of these effects. We investigate the pulsational and magnetic field properties of beta Cas. We also determine the star's apparent fundamental parameters and chemical abundances. Based on photometric time series obtained from three different space missions (BRITE-Constellation, SMEI, and TESS), we conduct a frequency analysis and investigate the stability of the pulsation amplitudes over four years of observations. We investigate the presence of a magnetic field and its properties using spectropolarimetric observations taken with the Narval instrument by applying the Least Square Deconvolution and Zeeman Doppler Imaging techniques. beta Cas shows only three independent p-mode frequencies down to the few ppm-level; its highest amplitude frequency is suggested to be a n=3, l=2, m=0 mode. Its magnetic field structure is quite complex and almost certainly of a dynamo origin. beta Cas' atmosphere is slightly deficient in iron peak elements and slightly overabundant in C, O, and heavier elements. Atypically for delta Scuti stars, we can only detect three pulsation modes down to exceptionally low noise levels for beta Cas.The star is also one of very few delta Scuti pulsators known to date to show a measurable magnetic field, and the first delta Scuti star with a dynamo magnetic field. These characteristics make beta Cas an interesting target for future studies of dynamo processes in the thin convective envelopes of F-type stars, of the transition region between fossil and dynamo fields, and the interaction between pulsations and magnetic field.
- ID:
- ivo://CDS.VizieR/J/AJ/160/32
- Title:
- beta Cephei light curves from KELT project
- Short Name:
- J/AJ/160/32
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a search for Galactic {beta} Cephei stars, which are massive pulsating stars with both pressure modes and mixed modes. Thus, these stars can serve as benchmarks for seismological studies of the interiors of massive stars. We conducted the search by performing a frequency analysis on the optical light curves of known O- and B-type stars with data from the Kilodegree Extremely Little Telescope exoplanet survey. We identify 113 {beta} Cephei stars, of which 86 are new discoveries, which altogether represent a 70% increase in the number currently known. An additional 97 candidates are identified. Among our targets, we find five new eclipsing binaries and 22 stars with equal frequency spacings suggestive of rotational splitting of nonradial pulsation modes. Candidates for runaway stars among our targets and a number of interesting individual objects are discussed. Most of the known and newly discovered {beta} Cephei stars will be observed by the Transiting Exoplanet Survey Satellite mission, providing by far the most comprehensive observational data set of massive main-sequence pulsating stars of sufficient quality for detailed asteroseismic studies. Future analysis of these light curves has the potential to dramatically increase our understanding of the structure of stellar interiors and the physical processes taking place therein.
- ID:
- ivo://CDS.VizieR/J/A+A/477/907
- Title:
- Beta Cephei stars in the ASAS-3 data. I.
- Short Name:
- J/A+A/477/907
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We analyse V-filter photometry of 41 known Beta Cephei-type stars. The ASAS-3 photometry is combined with the archival data, if available, to determine long-term stability of periods and amplitudes of excited modes. We detected amplitude changes in three Beta Cephei stars, BW Cru, V836 Cen, and V348 Nor. Period changes were found in KK Vel and V836 Cen. Our analysis shows that intrinsic period changes are more common among multiperiodic stars, apparently because they are caused by some kind of mode interaction. In addition, we found new modes for seven stars, and for ten others we provide new solutions or remove ambiguities in the detected frequencies. One candidate hybrid Beta Cephei/SPB star, HD 133823, is discovered.
- ID:
- ivo://CDS.VizieR/J/A+A/477/917
- Title:
- Beta Cephei stars in the ASAS-3 data. II.
- Short Name:
- J/A+A/477/917
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We analysed ASAS-3 photometry of bright early-type stars with the goal of finding new Beta Cephei stars. We were particularly interested in Beta Cephei stars that would be good for seismic analysis, i.e., stars that (i) have a large number of excited modes, (ii) show rotationally split modes, (iii) are components of eclipsing binary systems, (iv) have low-frequency modes, that is, are hybrid Beta Cephei/SPB stars. Our study was made with a homogeneous sample of over 4100 stars having MK spectral type B5 or earlier. For these stars, the ASAS-3 photometry was analysed by means of a Fourier periodogram. We have discovered 103 Beta Cephei stars, nearly doubling the number of previously known stars of this type. Among these stars, four are components of eclipsing binaries, seven have modes equidistant or nearly equidistant in frequency. In addition, we found five Beta Cephei stars that show low-frequency periodic variations, very likely due to pulsations. We therefore regard them as candidate hybrid Beta Cephei/SPB pulsators. All these stars are potentially very useful for seismic modeling. Moreover, we found Beta Cephei-type pulsations in three late O-type stars and fast period changes in one, HD 168050.
- ID:
- ivo://CDS.VizieR/J/A+A/543/A98
- Title:
- {beta} Gem radial velocity and photometric data
- Short Name:
- J/A+A/543/A98
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Our aim is to use precise radial velocity measurements and photometric data to derive the frequency spacing of the p-mode oscillation spectrum of the planet-hosting star beta Gem. This spacing along with the interferometric radius for this star can then be used to derive an accurate stellar mass.
- ID:
- ivo://CDS.VizieR/J/AJ/110/1350
- Title:
- Beta Lyrae light curve changes
- Short Name:
- J/AJ/110/1350
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We apply a variety of classical and recently developed periodicity analyses to light curves of Beta Lyrae in 9 eras that extend over a range of about 150 years. Some new data are tabulated. Most periodic variations that have been reported in the literature do not pass standard significance tests, according to our adopted criteria. Certain other periods do pass the tests, although most do so only for one, or at most two, data sets. Our main findings are that a period of about 9 months is present in all data sets and that it connects extremely well in phase from era to era, all the way back to Baxendell's observations of 1840-1877. The semiamplitude is small but reasonably consistent, averaging about 2% of the flux in the light curve maxima. Any substantially larger excursions that occur are nonperiodic. Phase coherence of the 9 month period is fairly good, even with a linear ephemeris, and becomes excellent if one allows for a slow sinusoidal variation of the 9 month periodicity. There is some evidence for a monotonic decrease in the amplitude of the 9 month periodicity with increasing wavelength.
1788. {beta} Lyr light curves
- ID:
- ivo://CDS.VizieR/J/A+A/618/A112
- Title:
- {beta} Lyr light curves
- Short Name:
- J/A+A/618/A112
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Mass exchange and mass loss in close binaries can significantly affect their evolution, but a complete self-consistent theory of these processes is still to be developed. Processes such as radiative shielding due to a hot-spot region, or a hydrodynamical interaction of different parts of the gas stream have been studied previously. In order to test the respective predictions, it is necessary to carry out detailed observations of binaries undergoing the largescale mass exchange, especially for those that are in the rapid transfer phase. {beta} Lyr A is an archetype of such a system, having a long and rich observational history. Our goal for this first study is to quantitatively estimate the geometry and physical properties of the optically thick components, namely the Roche-lobe filling mass-losing star, and the accretion disk surrounding the mass-gaining star of {beta} Lyr A. A series of continuum visible and NIR spectro-interferometric observations by the NPOI, CHARA/MIRC and VEGA instruments covering the whole orbit of {beta} Lyr A acquired during a two-week campaign in 2013 were complemented with UBVR photometric observations acquired during a three-year monitoring of the system. We included NUV and FUV observations from OAO A-2, IUE, and Voyager satellites. All these observations were compared to a complex model of the system. It is based on the simple LTE radiative transfer code SHELLSPEC, which was substantially extended to compute all interferometric observables and to perform both global and local optimization of system parameters. Several shapes of the accretion disk were successfully tested - slab, wedge, and a disk with an exponential vertical profile - and the following properties were consistently found: the radius of the outer rim is 30.0+/-1.0R_{sun}_, the semithickness of the disk 6.5+/-1.0R_{sun}_, and the binary orbital inclination i=93.5+/-1.0deg. The temperature profile is a power-law or a steady-disk in case of the wedge geometry. The properties of the accretion disk indicate that it cannot be in a vertical hydrostatic equilibrium, which is in accord with the ongoing mass transfer. The hot spot was also detected in the continuum but is interpreted as a hotter part of the accretion disk illuminated by the donor. As a by-product, accurate kinematic and radiative properties of Lyr B were determined.
- ID:
- ivo://CDS.VizieR/J/A+A/312/879
- Title:
- Beta Lyr radial velocities and UBV data
- Short Name:
- J/A+A/312/879
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A preliminary analysis of an extensive collection of interferometric, spectroscopic and photometric observations of the bright Be star {beta} Lyr lead to the following main conclusions: (1) The bulk of the H{alpha} and He I 6678 emission seems to originate in jets of material perpendicular to the orbital plane of the binary. The jets are associated with the more massive component of the binary (star 1) and probably emanate from the `hot spot' in the disk, i.e. the region of interaction of the gas stream flowing from the Roche-lobe filling B6-8II component (star 2) toward star 1. Some contribution to the emission also comes from a region located between the two stars (the gas stream and the `hot spot') and from the `pseudoatmosphere' of the accretion disk around star 1. (2) The 282-d cyclic variation of the light curve of {beta} Lyr is confirmed on the basis of 2852 homogenized V-band observations covering an interval of 36yrs. We find, however, that the amplitude and phase of these variations vary with the orbital phase: the long-term modulation of the light curve almost disappears near orbital phases 0.25P and 0.50P (elongation and secondary eclipse). (3) Pronounced line-profile variations of the H{alpha} and He I 6678 lines on a time scale shorter than one orbital period were clearly detected. They may be periodic, with a period near 4.70-4.75d, and this periodicity may be related to the 282-d change via the orbital period.
- ID:
- ivo://CDS.VizieR/J/AJ/140/119
- Title:
- {beta}Pic and AB Dor moving groups members
- Short Name:
- J/AJ/140/119
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results from our continuing program to identify new, low-mass, members of the nearby young moving groups (NYMGs) using a proper motion selection algorithm and various observational techniques. We have three goals: (1) to provide high priority targets for exoplanet searches by direct imaging, (2) to complete the census of the membership in the NYMGs down to ~0.1M_{sun}_, and thus (3) provide a well-characterized sample of nearby (median distances at least twice as close as the Taurus and Ophiuchus star-forming regions), young (8-50Myr) stars for detailed study of their physical properties and multiplicity.
