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Photometric Variability in a Sample of 187 G and K Giants
We have used three automatic photoelectric telescopes to obtainphotometric observations of 187 G, K, and (a few) M0 field giants. Wefind low-amplitude photometric variability on timescales of days toweeks on both sides of the coronal dividing line (CDL) in a total of 81or 43% of the 187 giants. About one-third of the variables haveamplitudes greater than 0.01 mag in V. In our sample the percentage ofvariable giants is a minimum for late-G spectral classes and increasesfor earlier and later classes; all K5 and M0 giants are variable. Wealso obtained high-resolution, red wavelength spectroscopic observationsof 147 of the giants, which we used to determine spectralclassifications, vsini values, and radial velocities. We acquiredadditional high-resolution, blue wavelength spectra of 48 of the giants,which we used to determine chromospheric emission fluxes. We analyzedthe photometric and spectroscopic observations to identify the cause(s)of photometric variability in our sample of giants. We show that thelight variations in the vast majority of G and K giant variables cannotbe due to rotation. For giants on the cool side of the CDL, we find thatthe variability mechanism is radial pulsation. Thus, the variabilitymechanism operating in M giants extends into the K giants up to aboutspectral class K2. On the hot side of the CDL, the variability mechanismis most likely nonradial, g-mode pulsation.
| The Photometric Variability of Sun-like Stars: Observations and Results, 1984--1995
Using differential Stromgren b, y photometry, we monitored thebrightness variations of 41 program stars and their 73 comparison starsfrom 1984 through 1995. The predominantly main-sequence program starsspanned ranges of temperature and mean chromospheric activity centeredon solar values. About 40% of all the stars showed measurablevariability, typically at levels below 0.01 mag (~1%), on bothnight-to-night and year-to-year timescales. The variability correlatedwith mean chromospheric activity and advancing spectral type. We presentdifferential light curves and statistical descriptions of ourobservations.
| Vitesses radiales. Catalogue WEB: Wilson Evans Batten. Subtittle: Radial velocities: The Wilson-Evans-Batten catalogue.
We give a common version of the two catalogues of Mean Radial Velocitiesby Wilson (1963) and Evans (1978) to which we have added the catalogueof spectroscopic binary systems (Batten et al. 1989). For each star,when possible, we give: 1) an acronym to enter SIMBAD (Set ofIdentifications Measurements and Bibliography for Astronomical Data) ofthe CDS (Centre de Donnees Astronomiques de Strasbourg). 2) the numberHIC of the HIPPARCOS catalogue (Turon 1992). 3) the CCDM number(Catalogue des Composantes des etoiles Doubles et Multiples) byDommanget & Nys (1994). For the cluster stars, a precise study hasbeen done, on the identificator numbers. Numerous remarks point out theproblems we have had to deal with.
| A narrow-band search for extraterrestrial intelligence (SETI) using the interstellar contact channel hypothesis
A search is reported for narrow spectral line emission from 176 targets(including 166 stars and seven globular clusers) at the hypothesized'interstellar communications channel' frequency of 4.462336275 GHz (= pitimes the neutral hydrogen line at 1.42 GHz) using the Parkes Radiotelescope. The frequency was Doppler corrected for the solar barycenter,target barycenter, and cosmic microwave background (CMB) referenceframes. If a 'Galactic club' of extraterrestrial civilizations exists,then the null results, down to a 3 sigma limit of 2 Jy (6 Jy in CMBframe), set an upper limit of 10 exp 8 yr on the lifetime of suchcivilizations.
| MK classifications for F-and G-type stars. 3.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1974AJ.....79..682H&db_key=AST
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תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | נשר |
| התרוממות ימנית: | 20h00m21.26s |
| סירוב: | +03°19'55.0" |
| גודל גלוי: | 6.707 |
| מרחק: | 662.252 פארסק |
| תנועה נכונה: | 1 |
| תנועה נכונה: | -15.4 |
| B-T magnitude: | 8.369 |
| V-T magnitude: | 6.845 |
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