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The Distribution of the Elements in the Galactic Disk. II. Azimuthal and Radial Variation in Abundances from Cepheids
This paper reports on the spectroscopic investigation of 101 Cepheids inthe Carina region. These Cepheids extend previous samples by about 35%in number and increase the amount of the Galactic disk coverageespecially in the direction of l ? 270°. The new Cepheids do notadd much information to the radial gradient, but provide a substantialincrease in azimuthal coverage. We find no azimuthal dependence inabundance over an 80° angle from the Galactic center in an annulusof 1 kpc depth centered on the Sun. A simple linear fit to the Cepheiddata yields a gradient d[Fe/H]/dRG = -0.055 ± 0.003dex kpc-1 which is somewhat shallower than found from ourprevious, smaller Cepheid sample.
| Searching Beyond the Obscuring Dust Between the Cygnus- Aquila Rifts for Cepheid Tracers of the Galaxy's Spiral Arms
A campaign is described, open to participation by interested AAVSOmembers, of follow-up observations for newly-discovered Cepheidvariables in undersampled and obscured regions of the Galaxy, a primaryobjective being to use these supergiants to clarify the Galaxy’sspiral nature. Preliminary multiband photometric observations arepresented for three Cepheids discovered beyond the obscuring dustbetween the Cygnus and Aquila Rifts (40° £ l £ 50°),a region reputedly tied to a segment of the Sagittarius-Carina arm whichappears to cease unexpectedly. The data confirm the existence ofexceptional extinction along the line of sight at upwards of AV ~- 6magnitudes (d ~- 2 kpc, l ~- 47°), however, the noted paucity ofoptical spiral tracers in the region does not arise solely fromincompleteness owing to extinction. A hybrid spiral map of the Galaxycomprised of classical Cepheids, young open clusters and H II regions,and molecular clouds presents a consistent picture of the Milky Way andconfirms that the three Cepheids do not populate the main portion of theSagittarius-Carina arm, which does not emanate locally from this region.The Sagittarius-Carina arm, along with other distinct spiral features,is found to deviate from the canonical logarithmic spiral pattern.Revised parameters are also issued for the Cepheid BY Cas, and it isidentified on the spiral map as lying in the foreground to most youngassociations in Cassiopeia. A Fourier analysis of the light curve of BYCas implies overtone pulsation, and the Cepheid is probably unassociatedwith the open cluster NGC 663 since the distances, ages, and radialvelocities do not match.
| Assessing potential cluster Cepheids from a new distance and reddening parametrization and Two Micron All Sky Survey photometry
A framework is outlined to assess Cepheids as potential cluster membersfrom readily available photometric observations. A relationship isderived to estimate colour excess and distance for individual Cepheidsthrough a calibration involving recently published Hubble SpaceTelescope parallaxes and a cleaned sample of established clusterCepheids. Photometric V - J colour is found to be a viable parameter forapproximating a Cepheid's reddening. The non-universal nature of theslope of the Cepheid period-luminosity relation for BV photometry isconfirmed. By comparison, the slopes of the VJ and VI relations seemrelatively unaffected by metallicity. A new Galactic Cepheid confirmedhere, GSC 03729-01127 (F6-G1 Ib), is sufficiently coincident with thecoronal regions of Tombaugh 5 to warrant follow-up radial velocitymeasures to assess membership. CCD photometry and O-C diagrams arepresented for GSC 03729-01127 and the suspected cluster Cepheids AB Camand BD Cas. Fourier analysis of the photometry for BD Cas and recentestimates of its metallicity constrain it to be a Population I overtonepulsator rather than a Type II s-Cepheid. AB Cam and BD Cas are notphysically associated with the spatially adjacent open clusters Tombaugh5 and King 13, respectively; the latter being much older (log? ~= 9)than believed previously. Rates of period change are determined for thethree Cepheids from archival and published data. GSC 03729-01127 and ABCam exhibit period increases, implying fifth and third crossings of theinstability strip, respectively, while BD Cas exhibits a perioddecrease, indicating a second crossing, with possible superposed trendsunrelated to binarity. More importantly, the observed rates of periodchange confirm theoretical predictions. The challenges and prospects forfuture work in this area of research are discussed.
| Galactic abundance gradients from Cepheids. On the iron abundance gradient around 10-12 kpc
Context: Classical Cepheids are excellent tracers of intermediate-massstars, since their distances can be estimated with very high accuracy.In particular, they can be adopted to trace the chemical evolution ofthe Galactic disk. Aims: Homogeneous iron abundance measurements for 33Galactic Cepheids located in the outer disk together with accuratedistance determinations based on near-infrared photometry are adopted toconstrain the Galactic iron gradient beyond 10 kpc. Methods: Ironabundances were determined using high resolution Cepheid spectracollected with three different observational instruments: ESPaDOnS@CFHT,Narval@TBL and FEROS@2.2m ESO/MPG telescope. Cepheid distances wereestimated using near-infrared (J,H,K-band) period-luminosity relationsand data from SAAO and the 2MASS catalog. Results: The least squaressolution over the entire data set indicates that the iron gradient inthe Galactic disk presents a slope of -0.052±0.003 textrm {dexkpc}-1 in the 5-17 kpc range. However, the change of the ironabundance across the disk seems to be better described by a linearregime inside the solar circle and a flattening of the gradient towardthe outer disk (beyond 10 kpc). In the latter region the iron gradientpresents a shallower slope, i.e. -0.012±0.014 textrm {dexkpc}-1. In the outer disk (10-12 kpc) we also found thatCepheids present an increase in the spread in iron abundance. Currentevidence indicates that the spread in metallicity depends on theGalactocentric longitude. Finally, current data do not support thehypothesis of a discontinuity in the iron gradient at Galactocentricdistances of 10-12 kpc. Conclusions: The occurrence of a spread in ironabundance as a function of the Galactocentric longitude indicates thatlinear radial gradients should be cautiously treated to constrain thechemical evolution across the disk.
| Reddenings of FGK supergiants and classical Cepheids from spectroscopic data
Accurate and homogeneous atmospheric parameters(Teff,logg,Vt, [Fe/H]) are derived for 74 FGKnon-variable supergiants from high-resolution, high signal-to-noiseratio, echelle spectra. Extremely high precision for the inferredeffective temperatures (10-40K) is achieved by using the line-depthratio method. The new data are combined with atmospheric values for 164classical Cepheids, observed at 675 different pulsation phases, takenfrom our previously published studies. The derived values are correlatedwith unreddened B - V colours compiled from the literature for theinvestigated stars in order to obtain an empirical relationship of theform (B - V)0 = 57.984 -10.3587(logTeff)2 +1.67572(logTeff)3 - 3.356logg +0.0321Vt + 0.2615[Fe/H] + 0.8833(logg)(logTeff).The expression is used to estimate colour excesses E(B - V) forindividual supergiants and classical Cepheids, with a precision of+/-0.05 mag for supergiants and Cepheids with n = 1-2 spectra, reaching+/-0.025mag for Cepheids with n > 2 spectra, matching uncertaintiesfor the most sophisticated photometric techniques. The reddening scaleis also a close match to the system of space reddenings for Cepheids.The application range is for spectral types F0-K0 and luminosity classesI and II.
| The Exciting Star of the Berkeley 59/Cepheus OB4 Complex and Other Chance Variable Star Discoveries
A study is presented regarding the nature of several variable starssampled during a campaign of photometric monitoring from the Abbey RidgeObservatory: three eclipsing binaries, two semiregulars, a luminous Bestar, and a star of uncertain classification. For one of the eclipsingsystems, BD+66°1673, spectroscopic observations reveal it to be anO5 V((f))n star and the probable ionizing star of the Berkeley 59/CepOB4 complex. An analysis of spectroscopic observations and BV photometryfor Berkeley 59 members in conjunction with published observations implya cluster age of ~2 Myr, a distance of d = 883 ±43 pc, and areddening of EB-V = 1.38 ±0.02. Two of theeclipsing systems are Algol-type, but one appears to be a cataclysmicvariable associated with an X-ray source. ALS 10588, a B3 IVn starassociated with the Cepheid SV Vul, is of uncertain classification,although consideration is given to it being a slowly pulsating B star.The environmental context of the variables is examined usingspectroscopic parallax, 2MASS photometry, and proper motion data, thelatter to evaluate the membership of the variable B2 Iabe star HDE229059 in Berkeley 87, an open cluster that could offer a uniqueopportunity to constrain empirically the evolutionary lineage of youngmassive stars. Also presented are our null results for observations of asample of northern stars listed as Cepheid candidates in the NewCatalogue of Suspected Variable Stars (NSV, in Samus et al. 2004).
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| Tycho-2 stars with infrared excess in the MSX Point Source Catalogue
Stars of all evolutionary phases have been found to have excess infraredemission due to the presence of circumstellar material. To identify suchstars, we have positionally correlated the infrared Mid-Course SpaceExperiment (MSX) Point Source Catalogue and the Tycho-2 opticalcatalogue. Near-mid-infrared colour criteria have been developed toselect infrared excess stars. The search yielded 1938 excess stars; overhalf (979) have never previously been detected by IRAS. The excess starswere found to be young objects such as Herbig Ae/Be and Be stars, andevolved objects such as OH/IR (infrared) and carbon stars. A number ofB-type excess stars were also discovered whose infrared colours couldnot be readily explained by known catalogued objects.
| Photometry of Type II Cepheids. III. The Intermediate-Period Stars
We present 741 new photometric observations for 22 Cepheids with periodsbetween 3 and 8 days. Many of the stars are probable type II Cepheids,but we have included some type I Cepheids for comparison. The shapes andstability of the shapes of the light curves, the stability of theperiods, and the scatter of individual data points are discussed.Although none of these proves to be a reliable discriminator betweentype I and type II Cepheids, they do permit the identification ofseveral unusual stars.
| Period-luminosity relations for Galactic Cepheid variables with independent distance measurements
In this paper, we derive the period-luminosity (PL) relation forGalactic Cepheids with recent independent distance measurements fromopen cluster, Barnes-Evans surface brightness, interferometry and HubbleSpace Telescope astrometry techniques. Our PL relation confirms theresults from recent works, which showed that the Galactic Cepheidsfollow a different PL relation to their Large Magellanic Cloud (LMC)counterparts. Our results also show that the slope of the Galactic PLrelation is inconsistent with the LMC slope with more than 95 per centconfidence level. We apply this Galactic PL relation to find thedistance to NGC 4258. Our result of μo= 29.49 +/- 0.06 mag(random error) agrees at the ~1.4σ level with the geometricaldistance of μgeo= 29.28 +/- 0.15 mag from water masermeasurements.
| The Distance Scale for Classical Cepheid Variables
New radii, derived from a modified version of the Baade-Wesselink (BW)method that is tied to published KHG narrowband spectrophotometry, arepresented for 13 bright Cepheids. The data yield a best-fittingperiod-radius relation given bylog=1.071(+/-0.025)+0.747(+/-0.028)logP0. In combination with other high-quality radiusestimates recently published by Laney & Stobie, the new data yield aperiod-radius relation described bylog=1.064(+/-0.0006)+0.750(+/-0.006)logP0, which simplifies to ~P3/4.The relationship is used to test the scale of Cepheid luminositiesinferred from cluster zero-age main-sequence (ZAMS) fitting, for whichwe present an updated list of calibrating Cepheids located in stellargroups. The cluster ZAMS-fitting distance scale tied to a Pleiadesdistance modulus of 5.56 is found to agree closely with the distancescale defined by Hipparcos parallaxes of cluster Cepheids and alsoyields Cepheid luminosities that are a good match to those inferred fromthe period-radius relation. The mean difference between absolute visualmagnitudes based on cluster ZAMS fitting,C, and those inferred for 23 clusterCepheids from radius and effective temperature estimates,BW, in the sense of C-BW is+0.019+/-0.029 s.e. There is no evidence to indicate the need for amajor revision to the Cepheid cluster distance scale. The absolutemagnitude differences are examined using available [Fe/H] data for thecluster Cepheid sample to test the metallicity dependence of theperiod-luminosity relation. Large scatter and a small range ofmetallicities hinder a reliable estimate of the exact relationship,although the data are fairly consistent with predictions from stellarevolutionary models. The derived dependence isΔMV(C-BW)=+0.06(+/-0.03)-0.43(+/-0.54)[ Fe/H].
| Using Cepheids to determine the galactic abundance gradient. I. The solar neighbourhood
A number of studies of abundance gradients in the galactic disk havebeen performed in recent years. The results obtained are ratherdisparate: from no detectable gradient to a rather significant slope ofabout -0.1 dex kpc-1. The present study concerns theabundance gradient based on the spectroscopic analysis of a sample ofclassical Cepheids. These stars enable one to obtain reliable abundancesof a variety of chemical elements. Additionally, they have welldetermined distances which allow an accurate determination of abundancedistributions in the galactic disc. Using 236 high resolution spectra of77 galactic Cepheids, the radial elemental distribution in the galacticdisc between galactocentric distances in the range 6-11 kpc has beeninvestigated. Gradients for 25 chemical elements (from carbon togadolinium) are derived. The following results were obtained in thisstudy. Almost all investigated elements show rather flat abundancedistributions in the middle part of galactic disc. Typical values foriron-group elements lie within an interval from ~-0.02 to ~-0.04 dexkpc-1 (in particular, for iron we obtainedd[Fe/H]/dRG =-0.029 dex kpc-1). Similar gradientswere also obtained for O, Mg, Al, Si, and Ca. For sulphur we have founda steeper gradient (-0.05 dex kpc-1). For elements from Zr toGd we obtained (within the error bars) a near to zero gradient value.This result is reported for the first time. Those elements whoseabundance is not expected to be altered during the early stellarevolution (e.g. the iron-group elements) show at the solargalactocentric distance [El/H] values which are essentially solar.Therefore, there is no apparent reason to consider our Sun as ametal-rich star. The gradient values obtained in the present studyindicate that the radial abundance distribution within 6-11 kpc is quitehomogeneous, and this result favors a galactic model including a barstructure which may induce radial flows in the disc, and thus may beresponsible for abundance homogenization. Based on spectra collected atMcDonald - USA, SAORAS - Russia, KPNO - USA, CTIO - Chile, MSO -Australia, OHP - France. Full Table 1 is only available in electronicform at http://www.edpsciences.org Table A1 (Appendix) is only, andTable 2 also, available in electronic form at the CDS via anonymous ftpto cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/381/32
| Stars with the Largest Hipparcos Photometric Amplitudes
A list of the 2027 stars that have the largest photometric amplitudes inHipparcos Photometry shows that most variable stars are all Miras. Thepercentage of variable types change as a function of amplitude. Thiscompilation should also be of value to photometrists looking forrelatively unstudied, but large amplitude stars.
| I- and JHK-band photometry of classical Cepheids in the HIPPARCOS catalog
By correlating the \cite[Fernie et al. (1995)]{F95} electronic databaseon Cepheids with the ``resolved variable catalog'' of the hipparcosmission and the simbad catalog one finds that there are 280 Cepheids inthe hipparcos catalog. By removing W Vir stars (Type ii Cepheids),double-mode Cepheids, Cepheids with an unreliable solution in thehipparcos catalog, and stars without photometry, it turns out that thereare 248 classical Cepheids left, of which 32 are classified asfirst-overtone pulsators. For these stars the literature was searchedfor I-band and near-infrared data. Intensity-mean I-band photometry onthe Cousins system is derived for 189 stars, and intensity-mean JHK dataon the Carter system is presented for 69 stars.
| Structural properties of s-Cepheid velocity curves Constraining the location of the omega_4 = 2omega_1 resonance
The light curves of the first overtone Pop. I Cepheids (s-Cepheids) showa discontinuity in their phi_ {21} vs. {P} diagram, near {P} = 3.2 day.This feature, commonly attributed to the 2:1 resonance between the firstand the fourth overtones (omega_4 ~ 2omega_1 ), is not reproduced by thehydrodynamical models. With the goal of reexamining the resonancehypothesis, we have obtained new CORAVEL radial velocity curves for 14overtone Cepheids. Together with 10 objects of Krzyt et al.( te{krzyt}), the combined sample covers the whole range of overtoneCepheid periods. The velocity Fourier parameters display a strongcharacteristic resonant behavior. In striking contrast to photometricones, they vary smoothly with the pulsation period and show no jump at3.2 day. The existing radiative hydrodynamical models match the velocityparameters very well. The center of the omega_4 = 2omega_1 resonance isestimated to occur at {P}r = 4.58\pm 0.04 day, i.e. at aperiod considerably longer than previously assumed (3.2 day). Weidentify two new members of the s-Cepheid group: MYPup and V440 Per. Based on observationscollected at the European Southern Observatory (La Silla, Chile) and atthe Observatoire de Haute-Provence (France)}
| A catalog of Cepheid radial velocities measured in 1995-1998 with the correlation spectrometer
We present a catalog of 2444 original radial-velocity measurements for108 Cepheids based on the 1995-1998 observations with the correlationspectrometer. Detailed radial-velocity curves are given for 12 Cepheidsfor the first time.
| Spectroscopic survey of field Type II Cepheids
A sample of relatively bright, short- and intermediate-period (P=1-10d)Type II Cepheids in the Galactic field have been observedspectroscopically with an intermediate-resolution(lambda/Deltalambda=11000) spectrograph. The wavelength region was6500-6700A, including the Hα line and some photospheric ironlines. The signal-to-noise ratio (S/N) was usually between 50 and 100,depending on weather conditions and the brightness of target stars.Radial velocities were determined by cross-correlating the Cepheidspectra with those of selected IAU velocity standard stars having F-Gspectral types. The internal error of the velocity determination processwas calculated to be about 1 km s^-1. Hα emission and strong linesplitting were observed in BL Her during the expansion phase, but nosimilar phenomenon was detected in any other stars in this programme,except for AU Peg which has an unusual Hα line showing a PCygni-like profile. The velocity curve agrees well with recent CORAVELmeasurements. The velocity gradients in Cepheid atmospheres are studiedusing the Hα minus metallic velocities. Similar data are collectedfrom the literature. It seems that having large velocity differences(v_Hα-v_metal>40 km s^-1) is a characteristic feature of thevery short-period (P<1.5d) and longer period (P>10d) Cepheids.Between these period regions the Cepheid atmospheres exhibit smallervelocity differences. Most of the Type II Cepheids observed in thepresent study fall into this latter category. There might be a tendencyfor classical Cepheids of intermediate period to have larger maximumvelocity differences.
| Monitoring the Evolution of Cepheid Variables
Described here are preliminary results of a pilot project to monitorchanges in the ephemerides of northern hemisphere Cepheid's using anSBIG camera attached to the 0.4-m telescope of the campus obversatory atSaint Mary's University. Epochs of maximum light for fifteen Cepheid'shave been derived using published light curves for each variable astemplates, and the results are being used to update the O-C ephemeridesfor the program stars. Results for BB Her are presented here. Periodchanges for Cepheid variables are demonstrated to be an excellent meansof pinpointing their evolutionary status, as well as for investigatingother peculiarities of the class.
| A catalog of Cepheid radial velocities measured in 1992-1995 with a correlation spectrometer
Not Available
| Mean radial velocities and binarity of cepheids from the 1987-1995 measurements
Not Available
| The Fourier decomposition of new light curves of Cepheids with P<7 D
In this paper the Fourier decomposition was applied to photoelectric andCCD measurements of faint Cepheids for which the light curve wassupplied for the first time with a sufficient accuracy. The Fourierdecomposition is confirmed to be a pulsation mode discriminator and thisproperty is discussed by considering also the case of the double-modeCepheid TU Cas. The analysis allowed us to detect three new firstovertone pulsators and to better define the behaviour of the Hertzsprungprogression for classical Cepheids with P<3 d. Some uncertainties areleft only for Cepheids located exactly on the discontinuity at P =~3 dand for Cepheids with an apparently perfect sinusoidal light curve. Atthe present time, the Fourier decomposition cannot be used todiscriminate safely between Pop. I and Pop. II stars. However, morenumerous and precise measurements should allow us to clarify also theseopen questions.
| The Behlen Observatory variable star survey: Finding charts and light curves for the first ninety-three stars
In a previous paper, photometry for the first ninety-three stars in aphotometric survey of variable stars was discussed. Finding charts,accurate coordinates, and light curves for those stars are presentedhere. The reliabilty of the coordinates from the General Catalogue ofVariable Stars is discussed. The magnitude scale of the presentphotometry is compared with that of the Hubble Space Telescope GuideStar Catalogue.
| Catalog of radial velocities for northern Cepheids measured with a correlation spectrometer
A catalog containing 1446 individual radial velocity values for 79 fieldCepheids and three Cepheids in globular clusters, and 32 averaged radialvelocities of the Cepheid Alpha UMi derived from 100 individual velocityparameters is presented. A table of gamma velocities for 30 Cepheidswith sufficiently good coverage of Vr curves is included. Radialvelocity observations of CE Cas A and CF Cas, which are photometricmembers of the open cluster NGC 7790, made it possible to estimate theradial velocity of the cluster (-78.0 km/s).
| The Behlen Observatory variable star survey - First results
Various light curve parameters are presented for the first 93 objects ina photometric survey of poorly studied variable stars. Stars from theGeneral Catalogue of Variable Stars (GCVS) fainter than tenth magnitude,north of the equator which were classified as pulsating variables (butexcluding the long period, semiregular, and irregular variables) wereincluded. It is shown that two parameters, the acuteness and the risetime, are useful for characterizing the light curves. Several criteriaare applied to the photometric data to test the classification of thestars. For 26 stars new or improved classifications are suggested. Inparticular, there are six eclipsing or ellipsoidal variables among the79 stars classed in the GCVS as RR Lyrae stars. This suggests that thereare likely to be four to five hundred binaries with short period whichare misclassified as RR Lyrae stars. Additionally, four stars arereclassified as Cepheids and three stars exhibit peculiarities whichmake their classification suspect. The periods of fourteen of the starsare found to be seriously in error while small adjustments for anadditional eighteen are made. The cause of these discrepancies isdiscussed.
| Color Excesses on a Uniform Scale for 328 Cepheids
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1990ApJS...72..153F&db_key=AST
| Some new results of cepheid studies.
Several research programs on cepheids are in progress in the USSR. Theauthors briefly characterize these programs and give some details aboutrecent results concerning radial velocity.
| A catalogue of field Type II Cepheids
A catalogue of field Type II Cepheids is presented. The primary listconsists of 152 Cepheids sufficiently far from the galactic plane to bevery probably Type II stars. A second list contains 56 additional starsthat are likely, but less certain, Type II Cepheids, including bothstars estimated to be at large distances from the galactic plane butwith uncertain distances and stars close to the galactic plane believedto be Type II for independent reasons.
| Period changes of Cepheid variables. I - Secular period changes
Secular period changes of one hundred northern Cepheids are investigatedwith the help of O-C diagrams. With the classical Cepheids the rate ofobserved period changes is in good agreement with that determined fromstellar evolution theory. The period noise cannot mask the evolutionaryperiod changes especially in longer period Cepheids for which theoccurrence of parabolic O-C graphs is unusually frequent.
| The Catalogue of Distances and Light Absorption for Cepheids
Not Available
| Photoelectric UBV Photometry of Northern Cepheids I
New UBV photoelectric observational data on 38 northern cepheids withperiods of less than 5 days are presented. The period changes of theobserved cepheids are investigated. Four variables (SU Cyg, DT Cyg, V532Cyg, SZ Tau) show a period jump and a subsequent 'rejump' to the earliervalue of the period, which results in the overall constancy of theperiod. DT Cyg pulsates with the same period for at least the fourthtime which is in keeping with the recent hypothesis on the evolution ofcepheids along the lines of constant period in the HRD. AU peg, aPopulation II variable, shows extremely strong period changes. In threecases, secular light curve variation was discovered. The amplitude ofthe light variation as AS Per is decreasing; the other type of lightcurve variation is the variation in the steepness of the rising branch(SU Cyg, FF Aql). The effect of the orbital motion on the O-C diagram isalso investigated for FF Aql. Finally, the instability of the period fordifferent types of cepheids is discussed.
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