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Rotational Velocity Determinations for 118 δ Scuti Variables
A calibration method is presented for the determination of projectedrotational velocities of 118 δ Scuti variables from FWHMmeasurements of metal lines near 4500 Å. The calibration relationused was derived from measurements of 29 stars. Of the 44 stars brighterthan 8th magnitude and north of –1° declination which did nothave values in the Rodríguez catalog (Rodríguez, E.,López González, M. J., & López de Coca, P.2000, A&AS, 144, 469) we present values for 38. In addition, wepresent new projected rotational velocity, vsin i, values for 10 starssouth of –1° or fainter than 8th magnitude for a total of 48vsin i values for stars with no previously published values.
| Pulsational properties of V2109 Cyg
In this study V2109 Cyg (a pulsating δ Scuti star) has beenmodelled. In treating the oscillation equations perturbation ingravitational potential energy has been taken into account. Both radialand nonradial oscillations are treated with adiabatic approximation. Theso called radial fundamental frequency (5.3745 c/d) and the nonradialfrequency (5.8332 c/d) were obtained within a satisfactory precision. Itwas found that the Cowling approximation introduced more error as onewent from low overtones to high overtones in radial oscillations. Asimilar trend was observed in nonradial case with low values of l. Bykeeping the effective temperatures almost the same as with V2109 Cyg twomore models with different masses have also been calculated to see theeffect of inclusion of perturbation in gravitational potential energy onoscillation frequencies in different masses. Conclusion arrived is thatone must be careful to employ the Cowling approximation especially forhigh nonradial oscillation frequencies.
| delta Sct-type nature of the variable V2109 Cyg
We present the results of simultaneous uvbybeta photometry carried outfrom 1999 to 2001 of the variable V2109 Cyg together with aspectroscopic analysis based on one high resolution spectrum obtained in2000. From this study, the star is definitively classified as an evolveddelta Sct-type variable with solar metal abundances. This conclusion isalso supported by the detected multiperiodic pulsational behaviour andthe observed variation of the m1 index over the pulsationcycle. This variation is slightly reversed relative to the V lightcurve, in very good agreement with the m1 variation expectedfrom the photometric calibrations. Besides the main frequencyf1=5.3745 cd-1 and its first harmonic2f1, a secondary peak is found at f2=5.8332cd-1 (f1/f2=0.92) with f1identified as a radial mode and f2 as non-radial. Whereas nosignificant variations are found in the amplitude of f1 fromseason to season, the amplitude of f2 changes strongly.Moreover, the main period has remained constant since 1990, within theobservational uncertainties. Additional secondary frequencies may alsobe excited in this variable.Based on observations collected at the Sierra Nevada, San PedroMártir and Haute-Provence observatories.Tables 2, 5 and 7 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi -bin/qcat?J/A+A/407/1059
| A photometric monitoring of bright high-amplitude delta Scuti stars. II. Period updates for seven stars
We present new photometric data for seven high-amplitude delta Scutistars. The observations were acquired between 1996 and 2002, mostly inthe Johnson photometric system. For one star (GW UMa), our observationsare the first since the discovery of its pulsational nature from theHipparcos data. The primary goal of this project was to update ourknowledge on the period variations of the target stars. For this, wehave collected all available photometric observations from theliterature and constructed decades-long O-C diagrams of the stars. Thistraditional method is useful because of the single-periodic nature ofthe light variations. Text-book examples of slow period evolution (XXCyg, DY Her, DY Peg) and cyclic period changes due to light-time effect(LITE) in a binary system (SZ Lyn) are updated with the newobservations. For YZ Boo, we find a period decrease instead of increase.The previously suggested LITE-solution of BE Lyn (Kiss &Szatmáry \cite{Kiss95}) is not supported with the new O-Cdiagram. Instead of that, we suspect the presence of transient lightcurve shape variations mimicking small period changes.
| A Revised Calibration of the MV-W(O I 7774) Relationship using Hipparcos Data: Its Application to Cepheids and Evolved Stars
A new calibration of the MV-W(O I 7774) relationship hasbeen calculated using better reddening and distance estimates for asample of 27 calibrator stars of spectral types A to G, based onaccurate parallaxes and proper motions from the Hipparcos and Tychocatalogues. The present calibration predicts absolute magnitude withaccuracies of +/-0.38mag for a sample covering a large range ofMV, from -9.5 to +0.35 mag. The color term included in aprevious paper has been dropped since its inclusion does not lead to anysignificant improvement in the calibration. The variation of the O I7774 feature in the classical cepheid SS Sct has been studied. Wecalculated a phase-dependent correction to random phase OI featurestrengths in Cepheids, such that it predicts mean absolute magnitudesusing the above calibration. After applying such a correction, we couldincrease the list of calibrators to 58 by adding MV and O Itriplet strength data for 31 classical Cepheids. The standard error ofthe calibration using the composite sample was comparable to thatobtained from the primary 27 calibrators, showing that it is possible tocalculate mean Cepheid luminosities from random phase observations ofthe O I 7774 feature. We use our derived calibrations to estimateMV for a set of evolved objects to be able to locate theirpositions in the HR diagram.
| The Period of V2109 Cyg Revisited
New observations of V2109 Cyg are used to determine the true pulsationperiod of this star. This observations are also consistent with noperiod changes since the Hipparcos era.
| Image-Subtraction Photometry of Variable Stars in the Field of the Globular Cluster NGC 6934
We present CCD BVI photometry of 85 variable stars from the field of theglobular cluster NGC 6934. The photometry was obtained with the imagesubtraction package ISIS. 35 variables are new identifications: 24 RRabstars, five RRc stars, two eclipsing binaries of W UMa-type, one SX Phestar, and three variables of other types. Both detected contact binariesare foreground stars. The SX Phe variable belongs most likely to thegroup of cluster blue stragglers. Large number of newly found RR Lyrvariables in this cluster, as well as in other clusters recentlyobserved by us, indicates that total RR Lyr population identified up todate in nearby galactic globular clusters is significantly (>30%)incomplete. Fourier decomposition of the light curves of RR Lyrvariables was used to estimate the basic properties of these stars. Fromthe analysis of RRc variables we obtain a mean mass of M=0.63Msolar, luminosity logL/Lsolar=1.72, effectivetemperature Teff=7300 and helium abundance Y=0.27. The meanvalues of the absolute magnitude, metallicity (on Zinn's scale) andeffective temperature for RRab variables are MV=0.81,[Fe/H]=-1.53 and Teff=6450, respectively. From the B-V colorat minimum light of the RRab variables we obtained the color excess toNGC 6934 equal to E(B-V)=0.09+/-0.01. Different calibrations of absolutemagnitudes of RRab and RRc available in literature were used to estimateapparent distance modulus of the cluster:(m-M)V=16.09+/-0.06. We note a likely error in the zero pointof the HST-based V-band photometry of NGC 6934 recently presented byPiotto et al. Among analyzed sample of RR Lyr stars we have detected ashort period and low amplitude variable which possibly belongs to thegroup of second overtone pulsators (RRe subtype variables). The BVIphotometry of all variables is available electronically via anonymousftp. The complete set of the CCD frames is available upon request. Basedon observations obtained with the 1.2 m Telescope at the F. L. WhippleObservatory of the Harvard-Smithsonian Center for Astrophysics.
| The Globular Cluster ω Centauri and the Oosterhoff Dichotomy
CCD observations obtained by the OGLE team for 128 RR Lyrae variables inω Centauri have been analyzed. The period-luminosity andperiod-amplitude plots indicate that, in addition to fundamental (RRab)and first overtone (RRc) pulsators, the ω Centauri RR Lyraepopulation seems to include second overtone (RRe) and possiblythird-overtone pulsators. The mean period for the 59 RRab stars is0.649°, for the 48 RRc stars, it is 0.383°, and for the 21 RRestars, it is 0.304°. The mean periods derived for the RRab and RRcstars are typical values for an Oosterhoff type II (OoII) cluster.Nevertheless, the period-amplitude plot also shows that some of the RRLyrae variables have ``Oosterhoff type I'' (OoI) characteristics. Mostof the second-overtone variables exhibit nonradial pulsations similar tothose recently detected in some of the RR Lyrae variables in theclusters M55 and M5, in the Galactic bulge, and in the LMC. Relativeluminosities derived for the RRc variables from Fourier coefficientscorrelate with the observed apparent magnitudes. Masses for the RRcstars have been calculated from Fourier coefficients. A comparison ofthe derived masses for RRc stars in the four OoII clusters ω Cen,M15, M55, and M68 indicates that the masses of the RRc stars in M15 andM68 are almost 0.2 Msolar greater than those in the othertwo. Since M15 and M68 have a high frequency of RRd stars among theirfirst-overtone pulsators, while none have been identified in ω Cenor M55, this suggests that the double-mode pulsation phenomenon may beassociated with mass. Among the RRc variables in ω Cen, the OoIIvariables have lower derived masses and higher luminosities than the OoIvariables. An application of the period-density law to pairs of OoI andOoII RRab stars selected according to their position in theperiod-amplitude plot also indicates that the OoII variables in generalhave lower masses and higher luminosities. These findings support thehypothesis that the RR Lyrae variables in OoII systems are evolvedhorizontal-branch stars that spend their zero-age horizontal-branchphase on the blue side of the instability strip.
| A revised catalogue of delta Sct stars
An extensive and up-dated list of delta Sct stars is presented here.More than 500 papers, published during the last few years, have beenrevised and 341 new variables have been added to our last list, sixyears ago. This catalogue is intended to be a comprehensive review onthe observational characteristics of all the delta Sct stars known untilnow, including stars contained in earlier catalogues together with othernew discovered variables, covering information published until January2000. In summary, 636 variables, 1149 references and 182 individualnotes are presented in this new list. Tables 1 and 2 will be accessibleonly in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Astrophysics in 1999
The year 1999 saw the arrival of a star with three planets, a universewith three parameters, and a solar corona that could be heated at leastthree ways. In addition, there were at least three papers on everyquestion that has ever been asked in astrophysics, from ``Will theUniverse expand forever?'' to ``Does mantle convection occur in one ortwo layers?'' The answers generally were, ``Yes,'' ``No,'' and ``None ofthe above,'' to each of the questions. The authors have done their bestto organize the richness around centers defined by objects, methods, andmadnesses.
| V2109 Cygni, a second overtone field RR Lyrae star
We present the first (as of February, 1999) UBV and uvby photometricmeasurements for the short period variable star V2109 Cyg discovered bythe Hipparcos satellite and classified as a field RRc variable. We haveobtained new times of maxima and the period change has been studied. Wedetermined the fundamental physical parameters using the geometricdistance of the star and the most recent synthetic colour grids. Theresults are: [Fe/H] = -0.9+/-0.2, Mbol=0.73+/-0.43 mag, =6800+/-200 K, log g=2.7+/-0.2, R=4.6+/-0.9 Rsun.Additionally, we took medium resolution (lambda /Delta lambda ~ 11000)spectra in the red spectral region centered at 6600 Angstroms. Acomplete radial velocity curve has been determined from 60 spectra. Wefound no systematic difference between the velocities from Hα andmetallic lines indicating a smooth pulsation. The mass of the star isfound to be M=0.5+/-0.3 Msun using the photometric log gvalue and the acceleration curve calculated from the radial velocitydata. The finally adopted set of the physical parameters lies in thetypical range of RR Lyrae stars, which implies that V2109 Cyg is theshortest period RR Lyrae-type variable. The visual amplitude vs. periodand the Fourier amplitude parameter R_21 vs. period diagrams suggestthat V2109 Cyg probably pulsates in the second overtone mode.
| The 74th Special Name-list of Variable Stars
We present the Name-list introducing GCVS names for 3153 variable starsdiscovered by the Hipparcos mission.
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Observation and Astrometry data
| Constellation: | Schwan |
| Right ascension: | 20h08m50.42s |
| Declination: | +48°54'39.4" |
| Apparent magnitude: | 7.499 |
| Distance: | 204.918 parsecs |
| Proper motion RA: | 4.7 |
| Proper motion Dec: | 16 |
| B-T magnitude: | 7.904 |
| V-T magnitude: | 7.533 |
Catalogs and designations:
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INHABITED SKY
