首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 223 毫秒
1.
We have carried out a search for co‐moving stellar and substellar companions around 18 exoplanet host stars with the infrared camera MAGIC at the 2.2 m Calar Alto telescope, by comparing our images with images from the all sky surveys 2MASS, POSS I and II. Four stars of the sample namely HD80606, 55 Cnc, HD46375 and BD–10°3166, are listed as binaries in the Washington Visual Double Star Catalogue (WDS). The binary nature of HD80606, 55 Cnc, and HD46375 is confirmed with both astrometry as well as photometry, thereby the proper motion of the companion of HD46375 was determined here for the first time.We derived the companion masses as well as the longterm stability regions for additional companions in these three binary systems. We can rule out further stellar companions around all stars in the sample with projected separations between 270AU and 2500AU, being sensitive to substellar companions with masses down to ∼60 MJup (S /N = 3). Furthermore we present evidence that the two components of the WDS binary BD–10°3166 are unrelated stars, i.e this system is a visual pair. The spectrophotometric distance of the primary (a K0 dwarf) is ∼67 pc, whereas the presumable secondary BD–10°3166B (a M4 to M5 dwarf) is located at a distance of 13 pc in the foreground. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

2.
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   

3.
We report Doppler measurements of the stars HD 187085 and HD 20782 which indicate two high eccentricity low-mass companions to the stars. We find HD 187085 has a Jupiter-mass companion with a ∼1000-d orbit. Our formal 'best-fitting' solution suggests an eccentricity of 0.47, however, it does not sample the periastron passage of the companion and we find that orbital solutions with eccentricities between 0.1 and 0.8 give only slightly poorer fits (based on rms and  χ2ν  ) and are thus plausible. Observations made during periastron passage in 2007 June should allow for the reliable determination of the orbital eccentricity for the companion to HD 187085. Our data set for HD 20782 does sample periastron and so the orbit for its companion can be more reliably determined. We find the companion to HD 20782 has   M sin   i = 1.77 ± 0.22  M Jup  , an orbital period of 595.86 ± 0.03 d and an orbit with an eccentricity of 0.92 ± 0.03. The detection of such high-eccentricity (and relatively low-velocity amplitude) exoplanets appears to be facilitated by the long-term precision of the Anglo-Australian Planet Search. Looking at exoplanet detections as a whole, we find that those with higher eccentricity seem to have relatively higher velocity amplitudes indicating higher mass planets and/or an observational bias against the detection of high-eccentricity systems.  相似文献   

4.
We present the results of speckle interferometry of a sample of 117 chemically peculiar stars with global magnetic fields. The observations were made in December 2009 at the BTA with a spatial resolution of about 0.02″ in the visual spectral region. Twenty-nine stars were resolved into individual components, 14 of them for the first time (HD965, HD5797, HD8855, HD10783, HD16605, HD21699, HD35502, HD51418, HD64486, HD79158, HD103498, HD108651, HD213918, HD293764). In twelve cases a companion turned out to be 2–4 m fainter than the main component—a magnetic star. Young hot Bp stars HD35502 and HD213918 are exceptions, since their companions are fainter by about 1 m . In all cases, the linear distance from a star to its companion at the epoch of observations in the picture plane exceeded 109 km. Eighty-eight magnetic CP stars revealed no secondary components within our study. Thus, the fraction of speckle interferometric binaries in our sample amounts to 25%.  相似文献   

5.
Low frequency oscillation, typical for γ Doradus g‐mode type stellar core sensitive pulsation, as well as higher frequency δ Scuti type pulsation typical for p ‐modes, sensitive to the envelope, make HD 8801 a remarkable hybrid pulsator with the potential to probe a stellar structure over a wide range of radius. In addition HD 8801 is a rare pulsating metallic line (Am) star. We determined the astro‐physical fundamental parameters to locate HD 8801 in the H‐R diagram. We analyzed the element abundances, paying close attention to the errors involved, and confirm the nature of HD 8801 as a metallic line (Am) star. We also determined an upper limit on the magnetic field strength. Our abundance analysis is based on classical techniques, but uses for the final step a model atmosphere calculated with the abundances determined by us. We also discuss spectropolarimetric observations obtained for HD 8801. This object is remarkable in several respects. It is a nonmagnetic metallic line (Am) star, pulsating simultaneously in p‐ and g‐modes, but also shows oscillations with periods in between these two domains, whose excitation requires explanation. Overall, the pulsational incidence in unevolved classical Am stars is believed to be quite low; HD 8801 does not conform to this picture. Finally, about 75 % of Am stars are located in short‐period binaries, but there is no evidence that HD 8801 has a companion. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

6.
Spectral observations of Ap-CP stars with the BTA (Special Astronomical Observatory, Russian Academy of Sciences) using the NES echelle spectrometer have revealed several stars with an anomalous lithium abundance. The oscillating star HD 12098, which is the first roAp star in the northern hemisphere of the sky, merits special attention. Strong, variable LiI 6708 Å line was observed in the spectrum of this star. There are not enough observations for a reliable analysis by Doppler mapping, but there are enough to indicate the presence of lithium spots on the surface of this star similar to the roAp stars HD 83368 and HD 60435, on whose surfaces spots with a high lithium abundance have been reliably detected. Parameters for a model of its atmosphere have been chosen using the method of synthetic spectra based on atmospheric models including lines from the VALD list and several additional blended REE lines calculated by the authors. The profile of the lithium LiI 6708 Å blend has been calculated taking the magnetic field into account using the SYNTHM code. A lithium abundance has been determined for two phases of the rotation of HD 12098 that is anomalously high compared to the solar and meteoritic abundances. The large difference in the lithium abundance in the two phases (in two different regions on the star's surface) exceeds 0.5 dex and is very close to that which we have found by analyzing the spectra of the roAp stars HD 83368 and HD 60435. Thus, we have discovered yet another roAp star, HD 12098, with lithium spots on its surface. Translated from Astrofizika, Vol. 51, No. 4, pp. 607–616 (November 2008).  相似文献   

7.
  相似文献   

8.
We report on our follow‐up spectroscopy of HD 1071478 B, a recently detected faint co‐moving companion of the exoplanet host star HD 107148 A. The companion is separated from its primary star by about 35″ (or 1790 AU of projected separation) and its optical and near infrared photometry is consistent with a white dwarf, located at the distance of HD 107148 A. In order to confirm the white dwarf nature of the co‐moving companion, we obtained follow‐up spectroscopic observations of HD 107148 B with CAFOS at the CAHA 2.2 m telescope. According to our CAFOS spectroscopy HD 107148 B is a DA white dwarf with an effective temperature in the range between 5900 and 6400K. The properties of HD 107148 B can further be constrained with the derived effective temperature and the known visual and infrared photometry of the companion, using evolutionary models of DA white dwarfs. We obtain for HD 107148 B a mass of 0.56 ± 0.05 M⊙, a luminosity of (2.0 ± 0.2) × 10–4 L⊙, log g [cm s–2]) = 7.95 ± 0.09, and a cooling age of 2100 ± 270 Myr. With its white dwarf companion the exoplanet host star HD 107148 A forms an evolved stellar system, which hosts at least one exoplanet. So far, only few of these evolved systems are known, which represent only about 5 % of all known exoplanet host multiple stellar systems. HD 107148 B is the second confirmed white dwarf companion of an exoplanet host star with a projected separation to its primary star of more than 1000 AU. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

9.
We search for stellar and substellar companions of young nearby stars to investigate stellar multiplicity and formation of stellar and substellar companions. We detect common proper‐motion companions of stars via multi‐epoch imaging. Their companionship is finally confirmed with photometry and spectroscopy. Here we report the discovery of a new co‐moving (13 σ) stellar companion ∼17.8 arcsec (350AU in projected separation) north of the nearby star HD141272 (21 pc).With EMMI/NTT optical spectroscopy we determined the spectral type of the companion to be M3±0.5V. The derived spectral type as well as the near infrared photometry of the companion are both fully consistent with a M⊙ dwarf located at the distance of HD141272 (21 pc). Furthermore the photometry data rules out the pre‐main sequence status, since the system is consistent with the ZAMS of the Pleiades. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

10.
Radial velocity curves have been measured for nine sdB stars from high resolution optical spectra and are found to be sinusoidal indicating that they are binary stars with circular orbits. Their periods range from ≈12 h to more than 8 days. The companions are invisible in optical light. Minimum companion masses are derived from the mass functions, assuming the mass of the sdB primary to be half a solar mass. We argue that the companions to UVO 1735+22, Feige 108, HD 188112, and HD 171858 are white dwarfs, since their (statistically) most likely mass is above ≈0.7M ⊙. Five of the systems have not been investigated before, for the others our results agree with previously published ones.  相似文献   

11.
We use an Artificial Neural Network (ANN) to derive the orbital parameters of spectroscopic binary stars. Using measured radial velocity data of four double‐lined spectroscopic binary systems HD 152218, HD 143511, HD 27149, and ER Vul, we find corresponding orbital and spectroscopic elements. Our numerical results are in good agreement with those obtained by others using more traditional methods (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

12.
Nainital-Cape Survey was started with an aim to search for new rapidly oscillating Ap stars in the northern hemisphere. We discovered one new mono-periodic roAp star HD 12098. The frequency separation of HD 12098 suggests a rotation period of 5.5 days for the star. We summarize here the observations of HD 12098 and briefly discuss the results of the multi-site observation campaign organized to resolve the ambiguity in the determination of the rotation period of HD 12098. Other interesting results like non-oscillating Ap stars discovered and two candidate stars in which roAp periodicity is seen but not confirmed are also discussed.  相似文献   

13.
Asteroseismology of pre-main-sequence δ Scuti stars has the potential not only to provide unprecedented constraints on models of these stars, but also to allow for the possibility of detecting evolutionary period changes, thus providing a direct measure of the pre-main-sequence evolutionary time-scale. In the last two years, the published number of such stars known has doubled from four to eight. Searches are now being conducted amongst the Herbig Ae stars, which are considered to be excellent candidates. We announce the discovery of δ Scuti pulsation in one Herbig Ae star, HD 142666, which lies within Marconi & Palla's theoretically predicted instability strip for pre-main-sequence stars, making this the ninth known pre-main-sequence δ Scuti star. We also demonstrate a lack of δ Scuti pulsation in another such star, HD 142527.  相似文献   

14.
I. S. Savanov 《Astrophysics》1996,39(2):107-111
The abundances of 12 elements in the atmosphere of the "F str 4077" star HD 177645 have been determined from new spectroscopic observations with the CCD camera and the model atmosphere method. The overabundance of nitrogen found for this star indicates its possible relation to barium dwarfs with anomalies in the chemical composition of their atmospheres due to mass transfer from the more evolved companion in a binary system. As an object related to Ba stars and CH subgiants, HD 177645 with an effective temperature Teff=7150K may also have anomalies in the chemical composition characteristic of diffusion processes in chemically peculiar stars of the upper main sequence, as may be indicated by the overabundance of sulfur in its atmosphere.Translated fromAstrofizika, Vol. 39, No. 2, pp. 201–209, April–June, 1996.  相似文献   

15.
From a set of stellar spectropolarimetric observations, we report the detection of surface magnetic fields in a sample of four solar-type stars, namely HD 73350, HD 76151, HD 146233 (18 Sco) and HD 190771. Assuming that the observed variability of polarimetric signal is controlled by stellar rotation, we establish the rotation periods of our targets, with values ranging from 8.8 d (for HD 190771) to 22.7 d (for HD 146233). Apart from rotation, fundamental parameters of the selected objects are very close to the Sun's, making this sample a practical basis to investigate the specific impact of rotation on magnetic properties of Sun-like stars.
We reconstruct the large-scale magnetic geometry of the targets as a low-order  (ℓ < 10)  spherical harmonic expansion of the surface magnetic field. From the set of magnetic maps, we draw two main conclusions. (i) The magnetic energy of the large-scale field increases with rotation rate. The increase in chromospheric emission with the mean magnetic field is flatter than observed in the Sun. Since the chromospheric flux is also sensitive to magnetic elements smaller than those contributing to the polarimetric signal, this observation suggests that a larger fraction of the surface magnetic energy is stored in large scales as rotation increases. (ii) Whereas the magnetic field is mostly poloidal for low rotation rates, more rapid rotators host a large-scale toroidal component in their surface field. From our observations, we infer that a rotation period lower than ≈12 d is necessary for the toroidal magnetic energy to dominate over the poloidal component.  相似文献   

16.
HD 111154 is a member of the Coma Cluster. It is here shown to be a somewhat unequal pair of stars of approximately solar type. They are in an orbit that has a period of just under 27 days and quite a high eccentricity (0.442). Although the minimum masses (1.08 and 1.00M ⊙) are large enough to encourage a search for eclipses, no such events have been detected.  相似文献   

17.
Time-series photometry of the Hipparcos variable stars HD 199434 and 21190 is reported. Both stars are pulsators of the δ Scuti type. Reclassifications of the MK types of the stars, based on new spectrograms, are given. HD 21190 is found to be F2III SrEuSi:, making it the most evolved Ap star known. Its Strömgren photometric indices support the peculiar spectral type. It is also one of the most evolved δ Scuti stars known. Its combined Ap– δ Scuti nature makes it an important test of models of pulsation in peculiar stars recently developed by Turcotte et al., although it is more extreme than any model they examined. Physical parameters of both stars are estimated from Strömgren and H β photometry, and Hipparcos absolute magnitudes. We attempt mode identifications based on amplitude ratios and phase differences from our photometry. The dominant pulsation of HD 21190 may be an overtone radial mode. The model fits for HD 199434 are even less satisfactory, but favour an ℓ=2 mode. Given the good quality and wavelength coverage of our data, the poor results from the application of the photometric theory of mode identification may call into question the use of that technique.  相似文献   

18.
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   

19.
The orbital elements of seven single‐lined spectroscopic binaries, HD 31855, HD 59643, HD 60092, HD 133189, HD 162262, HD 203522, BD +43° 1331 are presented. They are obtained from observations made with two photoelectric spectrometers of CORAVEL type, the first located at the Observatoire de Haute‐Provence and the second at the Cambridge Observatories. From those orbital elements and other data available in the literature, we deduce some information about the unseen companions and their separations with respect to the primaries. We then discuss the rotation‐revolution synchronism and conclude that some of those stars have probably reached the state of (pseudo‐)synchronism. Finally we give a synopsis of the results obtained in this series of papers. Our radial velocity monitoring of more than three decades has allowed us to derive accurate orbital elements of 35 spectroscopic binaries, with a cool primary star of type F‐G‐K‐M. The corresponding range of periods varies from a few days to more than 10 years. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

20.
We have searched for new members of the TWHya association (TWA) among unidentified ROSAT X‐ray sources by identifying them in proper motion catalogues and selecting those that would be consistent with kinematical membership to the TWA. Spectroscopic follow‐up observations of 19 member candidates revealed the detection of moderate lithium absorption lines for the following three stars: GSC 7206 845, TYC 7216‐55, and TYC 7247‐12. The isochronal ages of the latter TYC stars are estimated to be ∼20 Myr while the other one has ∼100 Myr age based on a kinematic distance estimate that assumes TWA membership. However, the moderately Li‐rich stars are not likely to be new pre‐main sequence members of TWA partly because of the discrepant radial velocities. Infrared follow‐up imaging in the H‐band for the 3 stars shows companion candidates near two of them.While one system (TYC 7216‐55) is probably a near‐equal‐magnitude stellar binary, our follow‐up H‐band spectrum of the faint companion candidate near GSC 7206 845 shows that it is instead a background K‐type star rather than a companion. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号