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Results from the Wide Angle Search for Planets Prototype (WASP0) - II. Stellar variability in the Pegasus field
Recent wide field photometric surveys, which target a specific field forlong durations, are ideal for studying both long- and short-periodstellar variability. Here, we report on 75 variable stars detectedduring the observations of a field in Pegasus using the Wide AngleSearch for Planets Prototype (WASP0) instrument, 73 of which are newdiscoveries. The variables detected include 16 δ Scuti stars, 34eclipsing binaries, 3 BY Draconis stars and 4 RR Lyraes. We estimatethat the fraction of stars in the field brighter than V~ 13.5 exhibitingvariable behaviour with an amplitude greater than 0.6 per cent rms is~0.4 per cent. These results are compared with other wide field stellarvariability surveys, and implications for detecting transits due toextra-solar planets are discussed.
| HD 8801: A Unique Single Am Star with γ Doradus and δ Scuti Pulsations
We have discovered the first example of a star pulsating intrinsicallywith both γ Doradus and δ Scuti frequencies. The star, HD8801, is an Am metallic-line star that appears to be single. Since thevast majority of Am stars are members of binary systems with periodsless than 1000 days and also do not pulsate, HD 8801 possesses a veryunusual, if not unique, combination of physical properties. Ourphotometry, acquired with an automatic telescope at FairbornObservatory, resolves six independent pulsation periods between 0.048and 0.404 days. The two longest periods lie within the range of γDor variables, while the four shorter periods are within the range ofδ Sct stars. Eleven radial velocities, obtained over an 11 monthperiod, have a mean of 0.8+/-0.3 km s-1, providing noevidence for a spectroscopic companion. The star is on the main sequenceand lies within both the γ Dor and δ Sct instability strips.Pulsation constants computed for the six periods agree with pulsationconstants computed for other γ Dor and δ Sct variables. HD8801 is also the first confirmed case of a metallic-line star pulsatingwith γ Dor frequencies. Its projected rotational velocity of 55 kms-1 is typical for Am stars, which, as a group, rotate moreslowly than normal A stars. HD 8801's slow rotation compared to normal Astars does not appear to arise from either a binary companion orevolutionary expansion and thus remains a puzzle. The coexistence ofmetallicism and pulsation in several main-sequence stars near the rededge of the δ Sct strip contradicts recent models that predictpulsations only in more evolved stars.
| Asteroseismology with robotic telescopes
Asteroseismology explores the interior of pulsating stars by analysingtheir normal mode spectrum. The detection of a sufficient number ofpulsation modes for seismic modelling of main sequence variablesrequires large quantities of high-precision time resolved photometry.Robotic telescopes have become an asset for asteroseismology because oftheir stable instrumentation, cost- and time-efficient operation and thepotentially large amounts of observing time available. We illustratethese points by presenting selected results on several types ofpulsating variables, such as δ Scuti stars (main sequence andpre-main sequence), γ Doradus stars, rapidly oscillating Ap starsand β Cephei stars, thereby briefly reviewing recent successstories of asteroseismic studies of main sequence stars.
| SX Phoenicis Stars in the Globular Cluster NGC 5466
Through time-series CCD photometry of the globular cluster NGC 5466, wehave detected nine SX Phoenicis stars, including three new ones. All theSX Phoenicis stars are located in the blue straggler region in thecolor-magnitude diagram of NGC 5466. Five of them clearly showdouble-radial mode features, the periods of which are consistent withthe theoretical ratio of the first-overtone mode to the fundamental mode(P1H/PF). Normally, it has not been easy to securea P-L relation for the SX Phoenicis stars because their pulsational modehas been difficult to determine. The existence of five SX Phoenicisstars in NGC 5466 with double-radial modes allows us to reliably derivea P-L relation for the fundamental mode of SX Phoenicis stars. Usingseven SX Phoenicis stars, including five stars with double-radial modes,we derive a P-L relation for the fundamental mode in NGC 5466,=-3.25(+/-0.46)logP+14.70(+/-0.06),(σ=+/-0.04),corresponding to =-3.25(+/-0.46)logP-1.30(+/-0.06)for an adopted distance modulus of (m-M)0=16.00 and zeroreddening.
| HD 207651: A Triple System with δ Scuti and Ellipsoidal Variations But No γ Doradus Pulsations
We examine HD 207651 as a possible example of a star exhibiting bothγ Doradus and δ Scuti type pulsations. We find photometricperiods of 0.06479 and 0.06337 days with peak-to-peak amplitudes inJohnson B of 21 and 13 mmag, respectively, clearly indicating δScuti pulsations. Additional light variation with a period of 0.73540days and an even larger amplitude of 31 mmag is within the range ofγ Doradus pulsation periods but results instead from theellipticity effect. HD 207651 has a composite spectrum with a weak,narrow absorption line superposed near the center of each broad metalline. The broad-lined component is the primary of a short-period,single-lined binary, which has a period of 1.4708 days, twice the periodof the ellipsoidal variations seen in the photometry. We determine theprimary to be an A8 giant and estimate the unseen secondary of theshort-period binary to be a mid-M dwarf. The narrow-lined star, an F7:dwarf, shows velocity variability with a period of months or perhapsyears. It is thus a more distant companion to the binary, making HD207651 a triple system. All light variations come from the A8 giantprimary star. Since the 0.73540 day variation results from theellipticity effect, HD 207651 is not an example of a star that exhibitsboth δ Scuti and γ Doradus pulsations. The growing number ofconfirmed γ Doradus stars that also occur within the δ Scutiinstability strip but fail to show additional δ Scuti variabilitymakes it increasingly unlikely that the two types of pulsation cancoexist in the same star.
| Spectroscopy of Early F Stars: γ Doradus Candidates and Possible Metallic Shell Stars
We obtained high-resolution spectroscopic observations of 34 γDoradus candidates. From the red-wavelength spectra, we determinedspectral classes, radial velocities, and projected rotationalvelocities. The spectra of seven late A or early F stars show metalliclines that have composite profiles consisting of a narrow component nearthe center of a broad line, indicating that they may be shell stars orbinaries. Several stars, including HD 152896, HD 173977, HD 175337, andHD 195068/9, show large line profile asymmetries. Two stars, HD 11443(=α Trianguli) and HD 149420, are ellipsoidal variables and notγ Doradus stars. The percentage of binary systems in our samplemay be as high as 74%.
| On the relationship between the δ Scuti and γ Doradus pulsators
We searched for δ Scuti-type pulsations amongst known andcandidate γ Doradus stars. The motivations for such a project comefrom the need to understand the relationship of these two classes ofpulsator better, from the present poor knowledge of the hot border ofthe γ Doradus phenomenon, and from the exciting prospects forasteroseismology should stars be found which have both types ofpulsation excited. We acquired 270h of observations and monitored atotal of 26 stars. One target, HD 209295, turned out to be a member ofboth classes of pulsating star, but this object is peculiar in the sensethat it is a close binary. We classify six of our targets as new bonafide γ Doradus stars, whereas nine more are good γ Doraduscandidates, and three turned out to be ellipsoidal variables. One of ourprogramme stars was found to be a δ Scuti star, with no additionalγ Doradus variations. Furthermore, one star was already known tobe a bona fide γ Doradus star, and we could not find anunambiguous explanation for the variability of five more stars. Theanalysis of our data together with improved knowledge of stars from theliterature enabled us to revise the blue border of the γ Doradusphenomenon towards cooler temperatures. This new blue edge is muchbetter defined than the previous one and extends from a temperature ofabout 7550K on the ZAMS to 7400K one magnitude above it. Five bona fideγ Doradus stars we observed are located inside the δ Scutiinstability strip, but none of them exhibited observable δ Scutipulsations. We therefore suggest that γ Doradus stars are lesslikely to be δ Scuti pulsators compared with other normal stars inthe same region of the lower instability strip. In addition, we showthat there is a clear separation between the pulsation constants Q ofδ Scuti and γ Doradus stars. The γ Doradus stars knownto date all have Q>0.23d.
| Multiperiodicities from the Hipparcos epoch photometry and possible pulsation in early A-type stars
A selection criterion based on the relative strength of the largestpeaks in the amplitude spectra, and an information criterion are used incombination to search for multiperiodicities in Hipparcos epochphotometry. The method is applied to all stars which have beenclassified as variable in the Hipparcos catalogue: periodic, unsolvedand microvariables. Results are assessed critically: although there aremany problems arising from aliasing, there are also a number ofinteresting frequency combinations which deserve further investigation.One such result is the possible occurrence of multiple periods of theorder of a day in a few early A-type stars. The Hipparcos catalogue alsocontains a number of these stars with single periodicities: such starswith no obvious variability classifications are listed, and informationabout their properties (e.g., radial velocity variations) discussed.These stars may constitute a new class of pulsators.
| New uvbybeta photometry of stars of ``astrophysical interest''
Not Available
| The domain of γ Doradus variables in the Hertzsprung-Russell diagram
70 new γ Doradus candidates were identified from Hipparcosphotometry, which represents more than a doubling of the presently knownnumber. Selecting the objects with good evidence for multiperiodicity,it is found that these stars, together with bona fide members of theclass, occupy a well-defined region in a colour-magnitude diagram. Thisdomain corresponds to a range of 7200-7700K on the zero-age mainsequence (ZAMS) and 6900-7500K one magnitude above it, which partlyoverlaps with the instability strip of δ Scuti stars. For thefirst time, γ Doradus stars can be discussed as a group. They canbe found over a significant fraction of the main sequence lifetimes forobjects in the relevant temperature range. An upper limit on the surfacemetallicity of γ Doradus stars is apparent, which may guide thesearch for their pulsation driving mechanism. The importance of possibleobjects exhibiting both γ Doradus and δ Scuti-typepulsations is discussed.
| Mesures de vitesses radiales. VIII. Accompagnement AU sol DU programme d'observation DU satellite HIPPARCOS
We publish 1879 radial velocities of stars distributed in 105 fields of4^{\circ} \times 4^{\circ}. We continue the PPO series \cite[(Fehrenbachet al. 1987;]{Feh87} \cite[Duflot et al. 1990, 1992 and 1995),]{Du90}using the Fehrenbach objective prism method. Table 1 only available inelectronic form at CDS via to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
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Observation and Astrometry data
| Constellation: | Pegasus |
| Right ascension: | 21h50m08.23s |
| Declination: | +19°25'26.4" |
| Apparent magnitude: | 7.22 |
| Distance: | 337.838 parsecs |
| Proper motion RA: | 56.4 |
| Proper motion Dec: | 9.9 |
| B-T magnitude: | 7.491 |
| V-T magnitude: | 7.243 |
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INHABITED SKY
