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Direct detection of exoplanet host star companion γ Cep B and revised masses for both stars and the sub-stellar object
Context: .The star γ Cep is known as a single-lined spectroscopictriple system at a distance of 13.8 pc, composed of a K1 III-IV primarystar with V = 3.2 mag, a stellar-mass companion in a 66-67 year orbit(Torres 2007, ApJ, 654, 1095), and a substellar companion withMp sin i = 1.7 M_Jup that is most likely a planet (Hatzes etal. 2003, ApJ, 599, 1383). Aims: .We aim to obtain a first directdetection of the stellar companion, to determine its current orbitalposition (for comparison with the spectroscopic and astrometric data),its infrared magnitude and, hence, mass. Methods: .We use theAdaptive Optics camera CIAO at the Japanese 8 m telescope Subaru onMauna Kea, Hawaii, with the semi-transparent coronograph to block mostof the light from the bright primary γ Cep A, and to detect at thesame time the faint companion B. In addition, we also used the IR cameraΩ Cass at the Calar Alto 3.5 m telescope, Spain, to image γCep A and B by adding up many very short integrations (without AO). Results: .γ Cep B is clearly detected on our CIAO and ΩCass images. We use a photometric standard star to determine themagnitude of B after PSF subtraction in the Subaru image, and themagnitude difference between A and B in the Calar Alto images, and findan average value of K = 7.3 ± 0.2 mag. The separations andposition angles between A and B are measured on 15 July 2006 and 11 and12 Sept. 2006, B is slightly south of west of A. Conclusions: .Bycombining the radial velocity, astrometric, and imaging data, we haverefined the binary orbit and determined the dynamical masses of the twostars in the γ Cep system, namely 1.40 ± 0.12Mȯ for the primary and 0.409 ± 0.018Mȯ for the secondary (consistent with being a M4 dwarf).We also determine the minimum mass of the sub-stellar companion to beMp sin i = 1.60 ± 0.13 M_Jup.
| Radial velocities. Measurements of 2800 B2-F5 stars for HIPPARCOS
Radial velocities have been determined for a sample of 2930 B2-F5 stars,95% observed by the Hipparcos satellite in the north hemisphere and 80%without reliable radial velocity up to now. Observations were obtainedat the Observatoire de Haute Provence with a dispersion of 80Ä,mm(-1) with the aim of studying stellar and galactic dynamics.Radial velocities have been measured by correlation with templates ofthe same spectral class. The mean obtained precision is 3.0 km s(-1)with three observations. A new MK spectral classification is estimatedfor all stars. Based on observations made at the Haute ProvenceObservatory, France and on data from The Hipparcos Catalogue, ESA.Tables 4, 5 and 6 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr or viahttp://cdsweb.u-strasbg.fr/Abstract.htm
| The Relation between Rotational Velocities and Spectral Peculiarities among A-Type Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJS...99..135A&db_key=AST
| The nature of the visual companions of AP and AM stars
The stars in 43 visual multiples with Ap or Am primaries have beenclassified, and the fraction of systems that have Ap or Am secondariesis counted. The numbers of Ap secondaries are too few to be informative,but an apparent excess of Am secondaries is found. That result isunderstandable in terms of the (published) moderate correlation inrotational velocities between components in visual multiples. But invarious open clusters, the variations in frequencies of Ap and Am starscan be explained probably as statistical fluctuations in small numbersof stars, indicating no tendency for abnormal stars to group togetherfor dimensions larger than those of visual multiples.
| Confirmation among visual multiples of an increase of AP stars with age
Open clusters with ages below certain threshold values contain no Apstars and those with greater ages contain numbers of Ap stars thatapparently increase with age. But in view of the few young clustersstudied, the data could also be interpreted in terms of randomdifferences in the frequencies of Ap stars between individual clusters,rather than an age effect. Data on 77 field visual multiple systems(that originated from many different clusters and associations) in whichthe primaries are O5-A1 stars and the secondaries occur in the absolutemagnitude range of the Ap stars were, therefore, obtained. Againspectral classification shows no Ap stars in systems with ages notgreater than 1,000,000 yr and a steady increase in Ap stars thereafter.The numerical agreement with the cluster data is good, confirming thatthe cluster data are exhibiting a real age effect.
| UVBY photometry of wide visual double stars with B, A and F spectral type- I.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1978A&AS...34..453O&db_key=AST
| Four-color and Hβ photometry for the brighter AO type stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1972A&AS....5..109C&db_key=AST
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Osservazione e dati astrometrici
| Costellazione: | Volpetta |
| Ascensione retta: | 21h10m30.95s |
| Declinazione: | +22°27'25.7" |
| Magnitudine apparente: | 7.41 |
| Distanza: | 347.222 parsec |
| Moto proprio RA: | 24.1 |
| Moto proprio Dec: | -11.3 |
| B-T magnitude: | 7.548 |
| V-T magnitude: | 7.422 |
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