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delta Scuti-type pulsation in the eclipsing and spectroscopic binary HD 172189 in the cluster IC 4756.
The binary system nature of the HD 172189 as well as the presence of thepulsating delta Scuti-type component in the system have beendiscovered. The great interest of this object lies in that threeimportant characteristics coexist: membership of the cluster IC 47456,binary and pulsation. An orbital period of 5.702 d has been found. Afrequency analysis of all the uvby out-of-primary-eclipse measurementsreveals a dominant frequency of 19.5974 c/d as well as high values inthe range of 18-20 c/d. In addition, it is located in the FOV of COROTmission, being a good candidate for its observation from space.
| HD 172189: an eclipsing and spectroscopic binary with a δ Sct-type pulsating component in an open cluster
We present a study based on more than 2500 uvby-measurements collectedon HD 172189, a new eclipsing binary system with a δ Sct-typepulsating component that belongs to the open cluster IC 4756. The greatinterest of this object lies in that three important characteristicscoexist: cluster membership, binarity and pulsation. Its binarity andthe δ Sct-type pulsations of one component were detected in thecourse of several Strömgren photometric campaigns. The frequencyanalysis of all the uvby out-of-eclipse data reveals a clear frequencyof 19.5974 cd-1as well as the existence of other high valuesin the range 18-20 cd-1. We have also carried out a firstevaluation of the binary parameters and determined a value of 5.702 dfor the orbital period. An additional potential interest of HD 172189resides in its location in the field of view of the COROT mission and,therefore, this star is an excellent candidate for becoming a target forasteroseismology.
| Preparing the COROT space mission: Incidence and characterisation of pulsation in the lower instability strip
By pursuing the goal to find new variables in the COROT field-of-view wecharacterised a sample of stars located in the lower part of theinstability strip. Our sample is composed of stars belonging to the diskpopulation in the solar neighbourhood. We found that 23% of the starsdisplay multiperiodic light variability up to a few mmag in amplitude,i.e., easily detectable on a single night of photometry. uvbybetaphotometry fixed most of the variables in the middle of the instabilitystrip and high-resolution spectroscopy established that they have vsin i>100 km s-1. An analysis of the Rodríguez &Breger (\cite{Rodr01}) sample (delta Sct stars in the whole Galaxy)shows slightly different features, i.e., most delta Sct stars have a0.05-mag redder (b-y)0 index and lower vsin i values.Additional investigation in the open cluster NGC 6633 confirms the sameincidence of variability, i.e., around 20%. The wide variety ofpulsational behaviours of delta Sct stars (including unusual objectssuch as a variable beyond the blue edge or a rapidly rotatinghigh-amplitude pulsator) makes them very powerful asteroseismic tools tobe used by COROT. Being quite common among bright stars, delta Sctstars are suitable targets for optical observations from space.Based on observations collected at the S. Pedro Martír, SierraNevada, La Silla, Haute-Provence, South African and Roque de LosMuchachos observatories.
| Radial velocity measurements. IV - Ground-based accompaniment to the HIPPARCOS observation program
The paper presents 396 radial velocities of stars distributed in 19fields of 4 x 4 degrees. The study employs the Fehrenbach objectiveprism method and the same measuring technique used in a previous paper(Fehrenbach et al., 1987).
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Observation and Astrometry data
| Constellation: | Οφιούχος |
| Right ascension: | 18h44m37.38s |
| Declination: | +07°58'39.4" |
| Apparent magnitude: | 7.971 |
| Proper motion RA: | 20.4 |
| Proper motion Dec: | 15.9 |
| B-T magnitude: | 8.252 |
| V-T magnitude: | 7.995 |
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