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1.
We present our extensive project of the On‐line database of photometric observations of magnetic chemically peculiar stars to collect published data of photometric observations of magnetic chemically peculiar (mCP) stars in the optical and near IR regions. Now the nascent database contains more than 107 000 photometric measurements of 102 mCP stars and will be continually supplemented with published or new photometric data on these and about 150 additional mCP stars. This report describes the structure and organization of the database. Moreover, for the all included data we estimated the error of measurements and the effective amplitudes of the light curves. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

2.
The “Nainital-Cape Survey” program for searching photometric variability in chemically peculiar (CP) stars was initiated in 1997 at ARIES, Nainital. We present here the results obtained to date. The Am stars HD 98851, HD 102480, HD 13079 and HD 113878 were discovered to exhibit δ Scuti type variability. Photometric variability was also discovered in HD 13038, for which the type of peculiarity and variability is not fully explained. The null results of this survey are also presented and discussed.  相似文献   

3.
We present the results of measurements of magnetic fields of chemically peculiar (CP) stars, performed from the shifts between the circularly polarized components of metal and hydrogen lines (the Babcock method). The observations are carried out with an analyzer of circular polarization at the 6‐m telescope of the SAO RAS. We found that for the absolute majority of the objects studied (in 22 CP stars out of 23), the magnetic fields, determined from the Zeeman shifts in the hydrogen line cores, are significantly lower than those obtained from metal lines in the same spectra. This disparity varies between the stars. We show that instrumental effects can not produce the above features, and discuss the possible causes of the observed effect. The discovered condition reveals a more complicated structure of magnetic fields of CP stars than a simple dipole, in particular, a reduction of the field strength in the upper atmosphere with the vertical gradient, significantly higher than the dipole (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

4.
This paper continues a series of reviews dedicated to magnetic CP stars. The occurrence frequency of CP stars among B5–F0-type main-sequence stars is shown to be equal to about 15–20%. The problems of identification and classification of these objects are addressed. We prefer the classification of Preston, which subdivides chemically peculiar stars into the following groups: Am, λ Boo, Ap/Bp, Hg-Mn, He-weak, and He-strong stars. The main characteristic features of objects of each group are briefly analyzed. The rotation velocities of CP stars are shown to be about three times lower than those of normal stars of the same spectral types (except for λ Boo and He-strong objects). The rotation periods of CP stars range from 0.5 to 100 days, however, there is also a small group of objects with especially long (up to several tens of years) variability periods. All kinds of peculiar stars can be found in visual binaries, with Am-and Hg-Mn-type stars occurring mostly in short-period binaries with P < 10 days, and the binary rate of these stars is close to normal. The percentage of binaries among magnetic stars (20%) is lower than among normal stars. A rather large fraction of CP1-and CP2-type stars was found to occur in young clusters (with ages smaller than 107 years). Photometric and spectral variability of peculiar stars of various types is discussed, and it is shown that only objects possessing magnetic fields exhibit light and spectral variations. The chemical composition of the atmospheres of CP stars of various types is considered. The abundances of various elements are usually determined by comparing the line profiles in the observed spectrum with those of the synthetic spectra computed for various model atmospheres. Different mechanisms are shown to contribute to chemical inhomogeneity at the star’s surface, and the hypothesis of selective diffusion of atoms in a stable atmosphere is developed. Attention is also paid to the problems of the determination of local chemical composition including the stratification of elements. Some of the coolest SrCrEu peculiar stars are found to exhibit fast light variations with periods ranging from 6 to 15 min. These variations are unassociated with rotation, but are due to nonradial pulsations. The final part of the the review considers the fundamental parameters of CP stars. The effective temperatures, luminosities, radii, and masses of these objects are shown to agree with the corresponding physical parameters of normal main-sequence stars of the same spectral types.  相似文献   

5.
We have analyzed more than 90 papers in the area “Magnetic fields and physical parameters of chemically peculiar and related stars,” published mainly in 2016. The main results of the period under survey are as follows. The search for new magnetic stars continued.Many measurements weremade at the 6-m BTA telescope of the SAO RAS, new data on stellar magnetism in the OrionOB1 association were obtained. A systematic study ofmagnetic fields of stars with large anomalies in the energy distribution in the continuum was started. New data on ultra-slowmagnetic rotators—chemically peculiar stars with rotation periods of years and decades are obtained. Successful observations on the search for new magnetic stars are performed among the objects of the southern sky in Chile at the FORS2 VLT spectropolarimeter. A new direction was developed, namely, the study of binarymagnetic stars. Depending on the mass–distance ratio between the components, interaction with the magnetosphere and, possibly, magnetic braking may occur. The study of the details of this process is important for the theory of formation of stellar magnetic fields. The search for large-scale, but weak magnetic fields (magnitude of unities and tens of G) in non-CP stars is ongoing. Such fields are found in Am stars. No fields were found in the classical Be stars. Cool stars of various types were studied in detail. They manifested magnetic fields of a complex structure. Their mapping was performed, changes in the topology of the field were found at timescales of several years. Spectral and photometric variability was studied. Dozens of new potentially magnetic stars are discovered as a result of the ASAS-3, SuperWASP, Stereo and Kepler surveys. High-accuracy observations of rapidly oscillating stars were performed with the BRITE nanosatellite.Work continued on the studies of magnetic and photometric variability of white dwarfs. Finally, an overview of several papers on exoplanets, related with the subject of our study is presented.  相似文献   

6.
It is essential for the understanding of stellar structure models of high mass stars to explain why constant stars, nonpulsating chemically peculiar hot Bp stars and pulsating stars co‐exist in the slowly pulsating B stars and β Cephei instability strips. We have conducted a search for magnetic fields in the four Bp stars HD55522, HD105382, HD131120, and HD138769 which previously have been wrongly identified as slowly pulsating B stars. A recent study of these stars using the Doppler Imaging technique revealed that the elements He and Si are inhomogeneously distributed on the stellar surface, causing the periodic variability. Using FORS 1 in spectropolarimetric mode at the VLT, we have acquired circular polarisation spectra to test the presence of a magnetic field in these stars. A variable magnetic field is clearly detected in HD55522 and HD105382, but no evidence for the existence of a magnetic field was found in HD131120. The presence of a magnetic field in HD138769 is suggested by one measurement at 3σ level. We discuss the occurrence of magnetic B stars among the confirmed pulsating B stars and find strong magnetic fields of order kG and oscillations to be mutually exclusive. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

7.
We continue our program of the study of large-scale structures of magnetic fields in chemically peculiar stars. In this paper we analyze eight stars, out of which three stars have the structure of a central dipole, three—the structure of a dipole shifted along the axis, and two—of a dipole shifted across the axis. High-precision measurements (with σ = 50 and 80 G) are available for two stars (HD62140 and HD71866, respectively). The model phase dependences agree with the measurements within the errors. This result shows that the hypothesis about the dipole structure of the magnetic fields of CP stars is well founded.  相似文献   

8.
To try to understand the behavior of helium variability in Chemically Peculiar stars, we continued our on‐going observational campaign started by Catanzaro, Leone & Catalano (1999). In this paper we present a new set of time resolved spectroscopic observations of the HeI5876 Å line for a sample of 10 stars in the spectral range B3 ‐ A2 and characterized by different overabundances. This line does not show variability in two stars: HD77350 and HD175156. It shows instead an equivalent width variation in phase with the Hipparcos light curve for two stars: HD79158 and HD196502. Antiphase variations have been found in 4 stars of our sample, namely: HD35502, HD124224, HD129174 and HD142990. Nothing we can say about HD115735 because of the constancy of Hipparcos photometric data, while no phase relation has been observed for HD90044. In the text we discuss the case of HD175156, according to photometric calibration and our spectroscopic observations we rule out the membership of this star to the main sequence chemically peculiar stars. We confirm the results obtained in the previous paper for which phase relations between light, spectral and magnetic variations are not dependent on stellar spectral type or peculiarity subclass.  相似文献   

9.
The first CCD photometric investigation of the open cluster NGC 7296 up to now was performed within the narrow band Δa photometric system, which enables us to detect peculiar objects. A deeper investigation of that cluster followed, using the standard BV R ‐Bessel filter set. The age and E (B – V ) was determined independently to log t = 8.0 ± 0.1 and 0.15 ± 0.02, respectively by using Δa and broadband photometry. In total five Be/Ae objects and two metal‐weak stars showing significant negative Δa ‐values as well as one classical chemically peculiar star could be identified within that intermediate age open cluster. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

10.
With the aim of investigating the possible particular behavior of carbon in a sample of chemically peculiar stars of the main sequence without turning to modeling, we performed spectroscopic observations of three important and usually prominent single ionized carbon lines: 4267.261, 6578.052 and 6582.882 Å. In addition, we observed a large number of standard stars in order to define a kind of normality strip, useful for comparing the observed trend for the peculiar stars. We paid particular attention to the problem of the determination of fundamental atmospheric parameters, especially for the chemically peculiar stars for which the abundance anomalies change the flux distribution in such a way that the classical photometric methods to infer effective temperatures and gravities parameter cannot be applied. Regarding CP stars, we found a normal carbon abundance in Hg–Mn, Si (with some exceptions) and He strong stars. He weak stars are normal too, but with a large spread out of the data around the mean value. A more complicated behavior has been noted in the group of SrCrEu stars: four out of seven show a strong overabundance, being the others normal.  相似文献   

11.
This is the first paper of the series dedicated to the analysis of the magnetism of chemically peculiar (CP) stars of the upper Main Sequence. We use our own measurements and published data to compile a catalog of magnetic CP stars containing a total of 326 objects with confidently detected magnetic fields and 29 stars which are very likely to possess magnetic field. We obtained the data on the magnetism of the overwhelming majority of the stars solely based on the analysis of longitudinal field component B e . The surface magnetic field, B s , has been measured for 49 objects. Our analysis shows that the number of magnetic CP stars decreases with increasing field strength in accordance with exponential law, and stars with B e exceeding 5kG occur rarely (about 3% objects of our list).  相似文献   

12.
Some difficulties in explaining the slow rotation of CP stars are discussed. The most likely hypotheses are (1) a loss of angular momentum involving a magnetic field during “pre-main sequence” evolution and (2) the slow rotation existed from the very start of the creation of these stars. The braking hypothesis is supported by only one property of CP stars— the lower the mass of the star is, the greater the difference between its average rotation velocity vsini and that of normal stars. On the other hand, there is another property— the lower the rotation speeds of CP stars are, the greater their fraction among normal stars. The latter property supports the hypothesis that the lower the initial rotation speed of a star is when it is created, the greater the probability will become chemically peculiar. This property is inherent in chemically peculiar stars both with and without a magnetic field. It is proposed that the cause of the slow rotation of CP stars must be sought in the very earliest phases of their formation, as should the cause of the separation into chemically peculiar magnetic, chemically peculiar nonmagnetic, and normal stars.__________Translated from Astrofizika, Vol. 48, No. 2, pp. 229–245 (May 2005).  相似文献   

13.
Our observations with the 6-m telescope revealed six new magnetic chemically peculiar (CP) stars among objects with large depressions in the continuum: HDE 293764, BD+17°3622, HD 169887, HDE 231054, HDE 338226, and HDE 343872. The presence of a magnetic field is suspected in several other CP stars. The maximum longitudinal field component B e exceeds 1.5 kG for all six stars; in HDE 293764 and HDE 343872, it reaches 3.8 kG. For each object, we present our magnetic-field measurements and published data on previous studies. The method of searching for magnetic stars based on an analysis of spectrophotometry shows its efficiency.  相似文献   

14.
The chemically peculiar (CP) stars of the upper main sequence are perfect tracers for several astrophysical processes. Their study especially in open clusters further helps to establish their evolutionary status. The latter is most important to understand the origin and evolution of the CP phenomenon, i.e. the connection between diffusion and a stellar magnetic field. There are two important topics, we cover with this paper. First of all, we investigate the reliability of the CCD Δa photometry for fainter objects in open clusters. The latter method is able to detect CP stars very efficiently, but still a spectroscopic verification is needed to verify the photometric candidates. On the other hand, already published spectral classifications on the basis of photographic plates and prism technology have tobe tested with modern instruments. Classification resolution spectroscopy is presented for thirty five bona‐fide CP candidates. Twenty six of them are located within the boundaries of fourteen open clusters, for which we also investigated their membership probabilities. Apart from five objects, they seem tobe members of the respective clusters. The objects were classified in the framework of a refined Morgan‐Keenan system with the extension of well established CP star spectra. We confirm the CP nature of all but one target. The results of Δa photometry and the spectral classifications are in excellent agreement. For the cluster members we find a continuous sequence of CP stars from 10 to 850 Myr, the whole range of investigated cluster ages (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

15.
The applications of the spectral analysis methods discovered by Kirchhoff for the investigation of stellar magnetic fields are considered. The statistical properties of the mean magnetic fields for OBA stars have been investigated by analyzing data from two catalogs of magnetic fields. It is shown that the mean effective magnetic field ℬ of a star can be used as a statistically significant characteristic of its magnetic field. The magnetic field distribution functions F(ℬ) have been constructed for B-type and chemically peculiar (CP) stars, which exhibit a power-law dependence on ℬ. A sharp decrease in F(ℬ) in the range of weak magnetic fields has been found. The statistical properties of the magnetic fluxes for main-sequence stars, white dwarfs, and neutron stars are analyzed.  相似文献   

16.
We present a first overview of variable stars in the Bochum Galactic Disk Survey (GDS) with emphasis on eclipsing binaries (EBs). This ongoing survey is performed by a robotic twin refractor at the Universitätssternwarte Bochum located near Cerro Armazones in Chile. It comprises a mosaic of 268 fields in a stripe of Δb = ±3° along the Galactic plane observed once per month simultaneously in the Sloan r and i filters with a detection limit of rs ∼ 16 mag and is ∼ 15 mag. The data from the first three years until the end of February 2014 yields a total of 41718 variable stars with variability amplitudes between 0.1–6 mag. A cross‐match with SIMBAD identified 11 465 of these variables unambiguously, while 2184 had multiple matches; most of the remaining stars could be matched with 2MASS objects. Among the SIMBAD‐listed objects with single matches, only 1982 turned out as known variables while a further 256 are suspected of variability. That leaves a total of 39480 potentially new variables. The group of known variables comprises 419 stars (21 %) that are classified as EBs while 443 (22%) are of other types; for the remaining 1120 catalogued variables (57 %) the type is unknown. Investigating variability as a function of spectral type, we find that SIMBAD provides spectral types for 2811 (25 %) of the identified stars. Spectral classes B (26 %), A (20 %), and M (25%) contain the most numerous variables, while all other classes contribute less than 10% each. More than half of the B (55 %) and A (56%) stars are designated as EBs, suggesting that hundreds of new B‐ and A‐type EBs may be contained in the GDS archive. In contrast, among the numerous M stars no EBs are known. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

17.
This paper presents a catalogue and the method of determining averaged quadratic effective magnetic fields  〈 B e〉  for 1212 main-sequence and giant stars, and 11 white dwarf stars. The catalogue includes stars that are members of several open clusters. We have compiled measurements of the longitudinal magnetic field for those stars, which were scattered in the existing literature. A new parameter, magnetization (MA), has been defined, and we present values of MA for stars of various spectral classes. Our sample includes a subset of 610 chemically peculiar early-type stars. We confirm the conclusion of our previous study that the number distribution of all chemically peculiar stars versus the averaged magnetic field strength is described by a decreasing exponential function. Relations of this type also hold for stars of all the analysed subclasses of chemical peculiarity. Magnetization tends to correlate with the effective temperature only at high MA, for He-weak and He-rich stars.  相似文献   

18.
We make a comparative analysis of magnetic fields and rotation parameters of magnetic CP stars with strong and weak anomalies in the spectral energy distribution. Stars with strong depressions in the continuum at 5200 Å are shown to have significantly stronger fields (the mean longitudinal component of the fields of these stars is 〈B e〉 = 1341 ± 98 G) compared to objects with weaker depressions (〈B e〉 = 645 ± 58 G). Stars with stronger depressions are also found to occur more commonly among slow rotators. Their rotation periods are, on the average, about 10 days long, three times longer than these of stars with weak depressions (about three days). This fact is indicative of a decrease of the degree of anomality of the magnetic stars continuum spectrum with increasing rotational velocity. Yet another proof has been obtained suggesting that slow rotation is one of the crucial factors contributing to the development of the phenomenon of magnetic chemically peculiar stars.Magnetic CP stars with weak depressions at 5200 Å are intermediate objects between stars with strong depressions and normal A- and B-type stars both in terms of field strength and rotational velocity.  相似文献   

19.
We re‐discuss the evolutionary state of upper main sequence magnetic stars using a sample of Ap and Bp stars with accurate Hipparcos parallaxes and definitely determined longitudinal magnetic fields. We confirm our previous results obtained from the study of Ap and Bp stars with accurate measurements of the mean magnetic field modulus and mean quadratic magnetic fields that magnetic stars of mass M < 3 M⊙ are concentrated towards the centre of the main‐sequence band. In contrast, stars with masses M > 3 M⊙ seem to be concentrated closer to the ZAMS. The study of a few known members of nearby open clusters with accurate Hipparcos parallaxes confirms these conclusions. Stronger magnetic fields tend to be found in hotter, younger and more massive stars, as well as in stars with shorter rotation periods. The longest rotation periods are found only in stars which spent already more than 40% of their main sequence life, in the mass domain between 1.8 and 3 M⊙ and with log g values ranging from 3.80 to 4.13. No evidence is found for any loss of angular momentum during the main‐sequence life. The magnetic flux remains constant over the stellar life time on the main sequence. An excess of stars with large obliquities β is detected in both higher and lower mass stars. It is quite possible that the angle β becomes close to 0. in slower rotating stars of mass M > 3 M⊙ too, analog to the behaviour of angles β in slowly rotating stars of M < 3 M⊙. The obliquity angle distribution as inferred from the distribution of r ‐values appears random at the time magnetic stars become observable on the H‐R diagram. After quite a short time spent on the main sequence, the obliquity angle β tends to reach values close to either 90. or 0. for M < 3 M⊙. The evolution of the obliquity angle β seems to be somewhat different for low and high mass stars. While we find a strong hint for an increase of β with the elapsed time on the main sequence for stars with M > 3 M⊙, no similar trend is found for stars with M < 3 M⊙. However, the predominance of high values of β at advanced ages in these stars is notable. As the physics governing the processes taking place in magnetised atmospheres remains poorly understood, magnetic field properties have to be considered in the framework of dynamo or fossil field theories. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

20.
We present a catalogue (CSOCA) of stars residing in 520 Galactic open cluster sky areas which is the result of the kinematic (proper motion) and photometric member selection of stars listed in the homogeneous All‐sky Compiled Catalogue of 2.5Million Stars (ASCC‐2.5).We describe the structure and contents of the catalogue, the selection procedure applied, and the proper motion and photometric membership constraints adopted. In every cluster area the CSOCA contains the complete list of the ASCC‐2.5 stars regardless of their membership probability. For every star the CSOCA includes accurate J2000 equatorial coordinates, proper motions in the Hipparcos system, BV photometric data in the Johnson system, proper motion and photometric membership probabilities, as well as angular distances from the cluster centers for about 166 000 ASCC‐2.5 stars. If available, trigonometric parallaxes, spectral types, multiplicity and variability flags from the ASCC‐2.5, and radial velocities with their errors from the Catalogue of Radial Velocities of Galactic Stars with high precision Astrometric Data (CRVAD) are also given. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

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