Context. Magnetic early B-type stars are rare. Indirect indicators are needed to identify them before investing in time-intensive spectropolarimetric observations. Aims. We use the strongest indirect ...indicator of a magnetic field in B stars, which is periodic variability of ultraviolet (UV) stellar wind lines occurring symmetric about the approximate rest wavelength. Our aim is to identify probable magnetic candidates which would become targets for follow-up spectropolarimetry to search for a magnetic field. Methods. From the UV wind line variability the B1/B2V star σ Lupi emerged as a new magnetic candidate star. AAT spectropolarimetric measurements with SEMPOL were obtained. The longitudinal component of the magnetic field integrated over the visible surface of the star was determined with the least-squares deconvolution method. Results. The UV line variations of σ Lupi are similar to what is known in magnetic B stars, but no periodicity could be determined. We detected a varying longitudinal magnetic field with amplitude of about 100 G with error bars of typically 20 G, which supports an oblique magnetic-rotator configuration. The equivalent width variations of the UV lines, the magnetic and the optical-line variations are consistent with the photometric period of 3.02 d, which we identify with the rotation period of the star. Additional observations with ESPaDOnS attached to the CFHT confirmed this discovery, and allowed the determination of a precise magnetic period. Analysis revealed that σ Lupi is a helium-strong star, with an enhanced nitrogen abundance and an underabundance of carbon, and has a chemically spotted surface. Conclusions.σ Lupi is a magnetic oblique rotator, and is a He-strong star. Like in other magnetic B stars the UV wind emission appears to originate close to the magnetic equatorial plane, with maximum emission occurring when a magnetic pole points towards the Earth. The 3.01972 ± 0.00043 d magnetic rotation period is consistent with the photometric period, with maximum light corresponding to maximum magnetic field.
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 \ell 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.
We present our analysis of photometric data in the Johnson B and V filter of the southern Blazhko star SS For. In parallel, we analysed the V observations obtained with the All Sky Automated Survey-3 ...photometry of the star gathered between 2000 and 2008. In the frequency spectra resulting from a Fourier analysis of our data, the triplet structure is detectable up to high order, both in the B and V data. Moreover, we find evidence for quintuplet components. We confirm from our data that the modulation components decrease less steeply than the harmonics of the main frequency. We derived the variations of the Fourier parameters quantifying the light-curve shape over the Blazhko cycle. There is good agreement between the spectroscopic abundance and the metallicity determined from the Fourier parameters of the average light curve. SS For is peculiar as a Blazhko star because of its strong variations around minimum light.
In an extended photometric campaign of RR Lyrae variables of the globular cluster M3, an aberrant-light-curve, non-Blazhko RRab star, V123, was detected. Based on its brightness, colors and ...radial-velocity curve, V123 is a bona fide member of M3. The light curve of V123 exhibits neither a bump preceding the light minimum, nor a hump on the rising branch, and has a longer than normal rise time, with a convex shape. A similar shape characterizes the mean light curves of some large-modulation-amplitude Blazhko stars, but none of the regular RRab variables with similar pulsation periods. This peculiar object thus mimics Blazhko variables without showing any evidence of periodic amplitude and/or phase modulation. We cannot find any fully convincing answer to the peculiar behavior of V123, however, the phenomenon raises again the possibility that rotation and aspect angle might play a role in the explanation of the Blazhko phenomenon, and that some source of inhomogeneity (magnetic field, chemical inhomogeneity) deforms the radial pulsation of Blazhko stars during the modulation.
Gaia Data Release 2 Prusti, T.; Evans, D. W.; Eyer, L. ...
Astronomy and astrophysics (Berlin),
08/2018, Letnik:
616
Journal Article, Web Resource
Recenzirano
Odprti dostop
Context.
We present the second
Gaia
data release,
Gaia
DR2, consisting of astrometry, photometry, radial velocities, and information on astrophysical parameters and variability, for sources brighter ...than magnitude 21. In addition epoch astrometry and photometry are provided for a modest sample of minor planets in the solar system.
Aims.
A summary of the contents of
Gaia
DR2 is presented, accompanied by a discussion on the differences with respect to
Gaia
DR1 and an overview of the main limitations which are still present in the survey. Recommendations are made on the responsible use of
Gaia
DR2 results.
Methods.
The raw data collected with the
Gaia
instruments during the first 22 months of the mission have been processed by the
Gaia
Data Processing and Analysis Consortium (DPAC) and turned into this second data release, which represents a major advance with respect to
Gaia
DR1 in terms of completeness, performance, and richness of the data products.
Results. Gaia
DR2 contains celestial positions and the apparent brightness in
G
for approximately 1.7 billion sources. For 1.3 billion of those sources, parallaxes and proper motions are in addition available. The sample of sources for which variability information is provided is expanded to 0.5 million stars. This data release contains four new elements: broad-band colour information in the form of the apparent brightness in the
G
BP
(330–680 nm) and
G
RP
(630–1050 nm) bands is available for 1.4 billion sources; median radial velocities for some 7 million sources are presented; for between 77 and 161 million sources estimates are provided of the stellar effective temperature, extinction, reddening, and radius and luminosity; and for a pre-selected list of 14 000 minor planets in the solar system epoch astrometry and photometry are presented. Finally,
Gaia
DR2 also represents a new materialisation of the celestial reference frame in the optical, the
Gaia
-CRF2, which is the first optical reference frame based solely on extragalactic sources. There are notable changes in the photometric system and the catalogue source list with respect to
Gaia
DR1, and we stress the need to consider the two data releases as independent.
Conclusions. Gaia
DR2 represents a major achievement for the
Gaia
mission, delivering on the long standing promise to provide parallaxes and proper motions for over 1 billion stars, and representing a first step in the availability of complementary radial velocity and source astrophysical information for a sample of stars in the
Gaia
survey which covers a very substantial fraction of the volume of our galaxy.
We present the results of a spectroscopic study of 37 southern (candidate) gamma Doradus stars based on echelle spectra. The observed spectra were cross-correlated with the standard template spectrum ...of an F0-type star for easier detection of binary and intrinsic variations. We identified 15 objects as spectroscopic binaries, including 7 new ones, while another 3 objects are binary suspects. At least 12 objects show composite spectra. We could determine the orbital parameters for 9 binaries, of which 4 turned out to be ellipsoidal variables. For 6 binaries, we estimated the expected time-base of the orbital variations. Clear profile variations were observed for 17 objects, pointing towards stellar pulsation. For 8 of them, we have evidence that the main spectroscopic and photometric periods coincide. Our results, in combination with prior knowledge from the literature, lead to the classification of 10 objects as new bona fide gamma Doradus stars, 1 object as a new bona fide delta Scuti star, and 8 objects as constant stars. Finally, we determined the projected rotational velocity by two independent methods. The resulting v sin i values range from 3 to 135 km s super(-1). For the bona fide gamma Doradus stars, the majority has v sin i below 60 km s super(-1).
Context. The CoRoT space mission (COnvection, ROtation and planetary Transits) launched in December 2006, aims at finding transiting exoplanets and investigating stellar oscillation in adjacent ...stellar fields, called exo- and seismofields, respectively. Besides the seismofields, CoRoT has a strong potential for seismological research on the exofields. Up to now, only a limited number of RR Lyrae stars have been classified among the CoRoT targets. Knowing the astrophysical importance of the RR Lyrae stars, we attempted to get useful information even from a contaminated light curve of a possible RR Lyrae pulsator. Aims. The star CoRoT 102781750 reveals a puzzle, showing a very complex and altering variation in different “CoRoT colours”. We established without doubt that more than a single star was situated within the CoRoT mask. Using a search for periodicity as a tool, our aim is to disentangle the composite light curve and identify the type of sources behind the variability. Methods. Both flux and magnitude light curves were used. Conversion was applied after a jump- and trend-filtering algorithm. We applied different types of period-finding techniques including MuFrAn and Period04. Results. The amplitude and phase peculiarities obtained from the independent analysis of CoRoT r, g, and b colours and ground-based follow-up photometric observations ruled out the possibility of either a background monoperiodic or a Blazhko type RR Lyrae star being in the mask. The main target, an active star, shows at least two spotted areas that reveal a Prot = 8.8 h (f0 = 2.735 c d-1) mean rotation period. The evolution of the active regions helped to derive a period change of dP/dt = 1.6 × 10-6 (18 s over the run) and a differential rotation of α = ΔΩ/Ω = 0.0074. The 0ṃ015 linear decrease and a local 0ṃ005 increase in the dominant period’s amplitude are interpreted as a decay of the old spotted region and an appearance of a new one, respectively. A star that is detected only in the CoRoT b domain shows a f1 = 7.172 c d-1 pulsation connected to a 14ḍ83 periodicity via an equidistant triplet structure. The best explanation for our observation is a β Cep star with a corotating dust disk.
Summary of the contents and survey properties Brown, A.G.A.; Granvik, Mikael; Zwitter, T.
Astronomy and astrophysics (Berlin),
2018, 2018-01-01, Letnik:
16, Številka:
A1
Journal Article
Recenzirano
Odprti dostop
Context. We present the second Gaia data release, Gaia DR2, consisting of astrometry, photometry, radial velocities, and information on astrophysical parameters and variability, for sources brighter ...than magnitude 21. In addition epoch astrometry and photometry are provided for a modest sample of minor planets in the solar system. Aims. A summary of the contents of Gaia DR2 is presented, accompanied by a discussion on the differences with respect to Gaia DR1 and an overview of the main limitations which are still present in the survey. Recommendations are made on the responsible use of Gaia DR2 results. Methods. The raw data collected with the Gaia instruments during the first 22 months of the mission have been processed by the Gaia Data Processing and Analysis Consortium (DPAC) and turned into this second data release, which represents a major advance with respect to Gaia DR1 in terms of completeness, performance, and richness of the data products. Results. Gaia DR2 contains celestial positions and the apparent brightness in G for approximately 1.7 billion sources. For 1.3 billion of those sources, parallaxes and proper motions are in addition available. The sample of sources for which variability information is provided is expanded to 0 : 5 million stars. This data release contains four new elements: broad-band colour information in the form of the apparent brightness in the G(BP) (330-680 nm) and G(RP) (630-1050 nm) bands is available for 1.4 billion sources; median radial velocities for some 7 million sources are presented; for between 77 and 161 million sources estimates are provided of the stellar effective temperature, extinction, reddening, and radius and luminosity; and for a pre-selected list of 14 000 minor planets in the solar system epoch astrometry and photometry are presented. Finally, Gaia DR2 also represents a new materialisation of the celestial reference frame in the optical, the Gaia-CRF2, which is the first optical reference frame based solely on extragalactic sources. There are notable changes in the photometric system and the catalogue source list with respect to Gaia DR1, and we stress the need to consider the two data releases as independent. Conclusions. Gaia DR2 represents a major achievement for the Gaia mission, delivering on the long standing promise to provide parallaxes and proper motions for over 1 billion stars, and representing a first step in the availability of complementary radial velocity and source astrophysical information for a sample of stars in the Gaia survey which covers a very substantial fraction of the volume of our galaxy.
Gaia Data Release 1 Brown, A G A; Vallenari, A; Prusti, T ...
Astronomy and astrophysics (Berlin),
11/2016, Letnik:
595
Journal Article, Web Resource
Recenzirano
Odprti dostop
Context. At about 1000 days after the launch of Gaia we present the first Gaia data release, Gaia DR1, consisting of astrometry and photometry for over 1 billion sources brighter than magnitude 20.7. ...Aims. A summary of Gaia DR1 is presented along with illustrations of the scientific quality of the data, followed by a discussion of the limitations due to the preliminary nature of this release. Methods. The raw data collected by Gaia during the first 14 months of the mission have been processed by the Gaia Data Processing and Analysis Consortium (DPAC) and turned into an astrometric and photometric catalogue. Results. Gaia DR1 consists of three components: a primary astrometric data set which contains the positions, parallaxes, and mean proper motions for about 2 million of the brightest stars in common with the Hipparcos and Tycho-2 catalogues - a realisation of the Tycho-Gaia Astrometric Solution (TGAS) - and a secondary astrometric data set containing the positions for an additional 1.1 billion sources. The second component is the photometric data set, consisting of mean G-band magnitudes for all sources. The G-band light curves and the characteristics of ~3000 Cepheid and RR Lyrae stars, observed at high cadence around the south ecliptic pole, form the third component. For the primary astrometric data set the typical uncertainty is about 0.3 mas for the positions and parallaxes, and about 1 mas yr super(-1) for the proper motions. A systematic component of ~0.3 mas should be added to the parallax uncertainties. For the subset of ~94000 Hipparcos stars in the primary data set, the proper motions are much more precise at about 0.06 mas yr super(-1). For the secondary astrometric data set, the typical uncertainty of the positions is ~10 mas. The median uncertainties on the mean G-band magnitudes range from the mmag level to ~0.03 mag over the magnitude range 5 to 20.7. Conclusions. Gaia DR1 is an important milestone ahead of the next Gaia data release, which will feature five-parameter astrometry for all sources. Extensive validation shows that Gaia DR1 represents a major advance in the mapping of the heavens and the availability of basic stellar data that underpin observational astrophysics. Nevertheless, the very preliminary nature of this first Gaia data release does lead to a number of important limitations to the data quality which should be carefully considered before drawing conclusions from the data.
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