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Intermediate Band Photometry of BB Lyrae Stars. II. Colors of RR Lyrae and Ultra-Short Period Variables

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... Early data of the star were published by Hoffmeister (1931), Robinson (1966), Clube et al. (1969), andJones (1973). From the ASAS photometry, a Blazhko period of about 97 days emerges for RU Cet. ...
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We report on differential photomultiplier photometry in the Johnson B and V filters of five southern Blazhko stars (RU Cet, RY Col, V674 Cen, AR Ser, RV Cap). The data were gathered from the South African Astronomical Observatory (SAAO) in Sutherland, South Africa, in the course of 2004 and 2005. To find the most reliable values for the periods, we combined our V data with ASAS photometry. For some stars, this enabled us to constrain their Blazhko period with unprecedented accuracy.
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Arguments are presented that the AI Velorum variables are about 0.2 M ⊙ objects evolving with a roughly constant luminosity toward the white dwarf stage.
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The period shift in both field and globular cluster RR Lyrae stars is examined. The stellar pulsation theory called the Sandage Period Shift to determine the mean M(V) of RR Lyrae stars is investigated. The advantages of (V-K) compared to (B-V) as a temperature indicator for RR Lyraes are discussed in detail. Period shift-metallicity relations are derived using recently published infrared photometry of field RR Lyraes and globular cluster RR Lyraes. Other method for determining mean M(V) for RR Lyraes are critically reviewed. It is argued that results for main sequence fitting, statistical parallax, and Red Giant Branch theory are presently too uncertain to be used. The slope of the mass-metallicity relation from pulsation theory is in serious disagreement with that from Horizontal Branch Theory.
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The variability and mass of the dwarf cepheid prototype, AI Vel, has been investigated during six nights of observations with the uvby beta filters. The two excited periods are found to have average amplitudes of 680 and 370 K, respectively. An average effective gravity of log g = 3.98 and an average effective temperature of 7620 K are found. The low-mass, high-evolution hypothesis is not confirmed for this star. The trigonometric parallax is too uncertain to determine the mass of this star. However, the metallicity index, space motion, and period-gravity relation indicate that AI Vel is in fact a delta Scuti star and in the immediate post-main-sequence (high-mass) phase of evolution.
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The Fourier techniques used by Faulkner (1977) in an analysis of photoelectric observations of U TrA, are applied to another well-observed beat Cepheid, TU Cas. It is found that there is a strong interaction between the primary and secondary pulsations. There is also a small-amplitude tertiary pulsation. The tertiary period suggests identification with the second-overtone radial mode. When the fundamental and second-overtone periods are used, the resulting beat mass agrees with the pulsation mass. The implications of this result are discussed.
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With a new sample of RRab Lyrae stars, the relation between metallicity and luminosity is refined and found to be $M_v = 0.12(\pm 0.04)\enspace \Delta S - 0.33(\pm 0.20)$ with $\sigma_\text M = 0.51 (\pm 0.18)$. We failed to find any relation between luminosity and period, confirming the result of Heck. The differences between the results of Clube & Dawe on one hand and our results on the other are mainly due to data differences and to dissimilarities in the adopted laws for the interstellar reddening.
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Photometric (uvbyfi) observations of the RRc variable SS Psc suggest that it is more closely related to dwarf cepheids (RRs stars) than to the RRc variables. Intrinsic (b — y) and c₁ values are employed to derive the variations in surface gravity and temperature. The mean values are (log g eff) = 3.29 and (T eff ) = 7300° K. The mi index, ((mi) 0 ) = 0.178, and spectrum indicate it is a metal-strong star.
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The paper modifies Sturch's (1966) method for deriving, from observed near-minimum light colors, EB-V values for RR Lyrae stars with Bailey's types for a or b light curves in order to avoid the use of reddening and metallicity-sensitive U-B colors. The Delta(S), (Fe/H) calibration is examined, and blanketing corrections are derived from synthetic colors of models by Kurucz (1975, 1979). Sturch's finding that the intrinsic blanketing-corrected near-minimum light B-V color of a variable can be estimated from its period is verified. The inherent accuracy of the method is discussed and found to depend appreciably on cycle-to-cycle color variations. Comparisons are made with other reddening determinations. The blanketing corrections determined by Sturch from delta(U-B) values are found to make his EB-V values less than those found in the present study, while his estimated intrinsic colors make his EB-V values greater than those found in this study.
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IR JHK light curves are presented for the RRab Lyrae stars UU Ceti, RV Phoenicis, and W Tucanae. These stars have similar periods and metallicities data, together with BVRI photometry and CORAVEL radial velocity data and Walraven photometry are used to derive absolute magnitudes for the stars using two formulations of the Baade-Wesselink method: (1) the infrared flux version and (2) the surface brightness version. The two methods are directly compared and their respective advantages and shortcomings are discussed. Finally, a comparison is made with previous results on the absolute magnitude of RR Lyrae variables.
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Simultaneous BVRI photometry and photoelectric radial velocities are presented for the dwarf cepheid AI Velorum. The Wesselink method of radius estimation yields a radius of 3.1 solar units. Pulsation properties deduced from the observations are compared with published models and found to be in good agreement with Population I masses.
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A radial velocity curve for CY Aqr, and VJK photometry for CY Aqr, YZ Boo, and VZ Cnc, are used to derive absolute magnitudes and masses for these three dwarf Cepheids. If dwarf Cepheids are early post-main-sequence stars, a pulsation mass of 1.2 + or - 0.3 solar masses is found, and the pulsation mass to evolutionary mass ratio is about 0.75. A mean value of -8.6 x 10 to the -11th days/day for the period changes is derived which is an order of magnitude larger than predicted by early post-main-sequence evolutionary tracks. Problems in modeling these stars at a more advanced evolutionary state are noted. Comparison is made between the properties of fundamental and possible overtone pulsators. The possible relationship between Delta Scuti behavior and the small cycle-to-cycle variations found in dwarf Cepheid light curves is also considered.
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Delta Scuti variable observational data concerning periods, period ratios, effective temperatures, gravities, radii, and metal abundances are compared with novel theoretical stellar evolution sequences, including a pulsation analysis for models in the lower Cepheid instability strip, in order to consider such physical properties as masses, ages, composition parameters, and the occurrence of helium-depleted outer zones. It is established that the metal-rich, high amplitude Delta Scuti variables are shell hydrogen-burning stars, and that the observed period ratios of double mode Delta Scuti variables can be explained by means of homogeneous standard models (although some helium depletion in surface zones is also possible). It is concluded that all evidence is in agreement with the assumption that Delta Scuti stars are evolving in accordance with standard stellar evolutionary theory.
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We have carried out a systematic study of the behavior of the Delta-m(1) metallicity parameter for SX Phe and high amplitude Delta Sct(pop. I) stars. It is shown that it has a different behavior for the two samples of stars. The Delta-m(1) parameter increases (SX Phe) or decreases (Delta Sct) towards minimum light for these two types of variables. Moreover, the m(1)-index variation is larger when the metal abundance of the star is smaller. An analogous effect is found in, other photometric indices.
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It is shown that the addition to the Stromgren four-color photometric system of three passbands at 374, 516 and 656 nm from the Vilnius photometric system makes the combined system more universal. This new system, called the Stromvil system, makes it possible to classify stars of all spectral types, even in the presence of interstellar reddening. This property of the system is especially important in CCD photometry, allowing the photometric classification of very faint stars. A preliminary calibration of the system in terms of spectral and luminosity classes, temperatures and surface gravities is available. A list of preliminary standards for the Stromvil system in the regions of Cygnus, Aquila and near the North Celestial Pole is given.
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New uvby-beta photometry of AD CMi covering several cycles is reported. No evidence for shock wave emission is detected in either the H beta line or in the Wesselink radius solutions. Due to the large acceleration at certain phases, a Wesselink analysis requires phases at equal temperatures, as opposed to phases of equal color. This explains the previously reported failure of the Wesselink method as well as the reported evidence for shock waves. The observed ultraviolet excess during the rising branch can be fully explained by effective gravity variations. A Wesselink radius of 3 solar radii is derived. This leads to a Population I mass. No evidence for a low-mass Population II nature exists for this star. Except for the large amplitude, the star is virtually indistinguishable from a normal delta Scuti variable.-
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The periods of delta Scuti, RR Lyrae, dwarf Cepheid, and W Virginis variables have been investigated for their dependence on luminosity, color, mass, and pulsation modes. A maximum-likelihood method, which includes consideration of the observational errors in each coordinate, has been applied to obtain observational period-luminosity-color (P-L-C) relations. (AIP)
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It is proposed that the maintenance of stable double-mode pulsation involves a resonant interaction between the two excited modes. This hypothesis yields a simple explanation of the narrow range of period ratio observed in both the double-mode Cepheids and the double-mode AI Velorum stars. The resonance idea is consistent with the under-massive models previously invoked to match the double-mode Cepheids, but seems to rule out normal Population I masses for the AI Velorum stars. It is argued that observational evidence regarding the pulsations of the AI Vel objects does not at present preclude the latter result.
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Results are reported for uvby-beta photometry of 10 distant early-type stars in the vicinity of the galactic globular cluster 47 Tucanae and the western edge of the Small Magellanic Cloud (SMC). The present study was undertaken to investigate the growth of interstellar reddening at large distances above the galactic plane and in front of the SMC. The derived (B - V) color excess between 1.2 and 4.6 kpc along the line of sight to 47 Tucanae is found to be in excellent agreement with a previous determination for the distance range from 0.20 to 0.52 kpc. It is concluded that: (1) the growth of reddening with increasing distance from the sun in the direction of 47 Tuc and the western edge of the SMC appears to have essentially stopped beyond 200 pc, remaining constant to a distance of the order of 10 kpc; (2) the reddening of 47 Tuc corresponds to a (B - V) color excess of 0.03 magnitude; and (3) the galactic contribution to the reddening of the SMC also corresponds to a (B - V) color excess of approximately 0.03.
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It is widely accepted that pulsating variables with periods less than 0.2 day fall into two distinct groups. These defined by Kukarkin et al. (1969) as, firstly, RRs:RR Lyrae type variables with the period not exceeding 0 d . 21 (dwarf Cepheids). Belong to the population of the disk, are absent in clusters. Their luminosity is 2 m –3 m fainter than the luminosity of RRab and RRc stars. A typical representative – SX Phe. and secondly, δSct:δScuti type stars. Pulsating variables of spectral class A (late sub-classes) and F, the amplitudes of light variation do not exceed, as a rule, 0 m .1 (rarely up to 0 m .3). The form of light curve strongly varies usually. According to many characteristics resemble dwarf Cepheids, but differ from them by the small amplitudes. Are met in the Hyades-type clusters. Similar to the RRs type stars their periods do not exceed 0 d .2. A typical representative – δSct.
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RR Lyrae stars: Normalized period-frequency diagrams are discussed, see Table I and Figure 1. Two ‘standard’ period-frequency relations were derived: one for − 1.17 and the other for − 1.72. The peculiarity of the diagrams for some clusters is pointed out. Various metallicity criteria are discussed together with other features of globular clusters. Some unexplained anomalies are found. W Virginis stars: Properties of these stars are discussed. They too seem not to form a homogeneous group. The lack of accurate observations is stressed.
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Stellar abundances are reviewed with emphasis on large-scale effects which may yield clues to galactic structure and evolution. Spectroscopic and indirect photoelectric abundance criteria are discussed, and utilized. The abundance statistics of nearby galactic disk stars, dominated by M dwarfs, but observed at spectral types F and GV and K III, suggest a weak age-abundance relationship with a substantial dispersion at any time. Very metal-poor stars are extremely rare. Spatial abundance gradients, with higher metal abundances occurring nearer the galactic centre, are indicated. Disk abundance gradients are prevalent for light elements in other Sb and Sc galaxies. The confusing status of supermetallicity is again reviewed. The super-metal-rich (SMR) giants (like μ Leo) are either over-abundant because of self-N-enrichment (from C–N–O processing?)and boundary-temperature cooling, or are really SMR. Each case may be reasonably argued. The old galactic clusters M67 and NGC 183 seem, by recent indirect acclaim, to be only slightly more metal-rich than the Sun. The Spinrad-Taylor data on the M67 giants would still seem to superficially suggest overabundances in Na and Mg, but other interpretations are possible. SMR dwarfs, like HR 72, and subgiants, like 31 Aql are surely very old, and have metal abundances larger than the Hyades. However, they are, by number, only ≈ 5% of the local main sequence. The galactic halo star tracers – red giants and RR Lyrae stars, have been observed extensively, lately. There is some indication of an abundance gradient from 5 or 10 kpc galactocentric radius out to r ~ 100 kpc. The most metal-poor stars observed in the Draco system are about 1000 times less abundant in heavy elements than is the Sun, and much of the galactic disk. Abundances in other galaxies, as a function of their total mass, and stellar/gaseous composition are also reviewed. There is a clear dependence of abundance on galaxian total mass.
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Theoretical problems in connection with δ Sct and RRs type variables are reviewed. All evidence shows that δ Sct stars are normal main-sequence or early post main-sequence stars. Results of linear stability analyses of δ Sct models agree well with observations, the presence of non-variables in the strip being understandable in terms of helium diffusion. Excitation of non-radial modes may also occur; comparison of observed multiple periodicities with the theoretically derived period patterns for radial and non-radial modes is discussed as a means to distinguish between these possibilities. It is not known whether RRs variables are of the same nature as δ Sct stars or in a late evolutionary state with low mass. RRs variables pulsate in radial modes, and recent linear stability analyses seem to agree well with observations for both normal and low masses. The reason for the difference in amplitude between RRs and δ Sct stars is not known. Non-linear investigations may provide important information in the near future. The observed period ratios of RRs variables indicate for most of the double mode pulsators a slight deficiency in heavy elements and a normal mass; but more detailed investigations of this problem are needed.
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We have developed a Baade–Wesselink method based on the Infrared Flux Method of Blackwell & Shallis. The method requires extensive photometry. However, if the data are available it can give accurate results. We have applied the method to the metal-poor RR Lyrae star X Arietis for which we also present new ultraviolet, optical and infrared photometry. We find $$\langle r\rangle = 6.00\pm0.45R_\odot$$, $$\langle T_\text e\rangle = 6390\pm190 \enspace\text K$$, $$\langle M_V\rangle = 0.47\pm0.19$$, $$\langle M_k\rangle = -0.63\pm0.16$$ and $$\langle M_\text{bol}\rangle = 0.41\pm0.19$$. Extensive comparison with the recent Baade–Wesselink analyses of X Ari by Manduca et al. and Jones et al. shows that, after correcting to the same reddening value and the same radial velocity conversion factor, the Manduca et al. result agrees with our estimate to 0.01 mag at $\langle M_V\rangle$. The Jones et al. result is 0.15 mag fainter. Several possible explanations for this difference are discussed.
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The variability of the dwarf cepheid VX Hya has been investigated during three nights using the uvby and beta filters. An average effective surface gravity of log g = 3.47 and an average surface temperature of 7000 K were found. The mean metallicity index of +0.003 magnitude indicates solar-type abundances. No evidence for a low-mass nature of this star is found from the metal abundance, period-gravity relation, and space motion. It is suggested that VX Hya is a large-amplitude delta Scuti star. Model-atmosphere calibrations of the uvby-beta indices using Kurucz's (1975) models and Breger's (1974) normalization are given.
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A bibliography of 775 papers concerning Strömgren four-color photometry and H Beta photometry is presented, covering the years 1950 – 1976. The papers are separated into the subject headings listed in and listed in order of abstract number
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Proposed evolutionary models of AI Velorum variables are reviewed, and further arguments are offered that these variables are about 0.2 solar mass stars evolving with a roughly constant luminosity toward the white dwarf stage after having lost most of their mass during the red giant phase. Such pre-white-dwarf configurations contain most of their mass in a degenerate helium core, but their luminosity is due almost exclusively to shell hydrogen burning.
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Possible red horizontal branch (HB) stars in the Galactic field are analyzed using the Vilnius intermediate land photometric system. Temperatures, luminosities and metallicities are given and the system is considered to be the most suitable to isolate red horizontal branch objects. Results show that the number of metal-rich stars on the red HB should exceed the number of metal-rich RR Lyrae-type stars. Eight stars are suspected to belong to the HB branch on the basis of seven color photometry. The spectral types were found to be within F5 and G2 and luminosities in between III and I classes. Most of the stars were classified as metal-deficient.
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A comprehensive study of the metal abundances and space motions on the high-amplitude delta Sct star V703 Sco has been carried out. Our results suggest this star is a normal high-amplitude delta Sct-type variable of Population I with nearly solar abundances and small space motions located in the galactic plane. This is in very good agreement with that suggested by the period ratio P_0/P_1=0.768 which takes place for its two main periodicities.
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Test made on four ITT FW-130 photomultipliers in the pulse-counting mode show that they are linear with respect to an RCA 1P21 to better than 0.002 magnitude per magnitude over a 7.5-magnitude range in brightness.
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Observational data for 170 Cepheids and 100 RR Lyrae stars south of declination +15 deg were obtained with the Walraven five-channel photometer and processed, and some implications of the data are considered. Evidence that there is a remarkably small range in composition for the short-period Pop I Cepheids supports the use of one intrinsic locus to derive reddenings for the 'classical' Cepheids. Double-mode Cepheids are found to have Pop I characteristics. The use of an algorithm to obtain the colors of the equilibrium configuration directly from the color curves is explained. For RR Lyrae stars, the use of deblanketed or blanketing-independent colors to determine the reddening is described.
Article
Some twenty years have passed since the decision was taken by the General Assembly of IAU in 1958 to resume a regular control of light variation stability in RR Lyrae stars. With this end in view the revision of elements is carried out at the Odessa Astronomical Observatory yearly, whereas ephemerides of RR Lyrae stars are published at the Krakov Observatory. Now 164 stars brighter than at maximum light visible in the northern hemisphere have entered the list. Considerable photometric observational material analyzed has shown that some RR Lyrae stars have stable periods of light variation (e.g. TV Lib, UY Cyg, SU Dra), while other ones have periods which vary regularly or proportionally to time (e.g. SV Eri, AV Peg, RV CrB) (Tsesevich, 1966; Firmanyuk, 1976; Romanov et al., 1978). In case of DR And at comparatively small amplitude of O-C variation, about 0.15, a synchronous variation in mean light at maximum nearly by has been found (Romanov, 1978). Unfortunately, necessary observational material is frequently unavailable to obtain the unambiguous classification of period stability character. The property of RR Lyrae stars light variation stability is connected with the weakening of KCall absorption line (Tsesevich, 1966, 1971).
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Low-resolution spectral measurements have been used to determine the temperature and relative radius variations in three pulsating stars of the Delta Sct class. The variations in the radii of Rho Pup and X Cae (HR 1653) are not quite in agreement with radial velocity measurements found in the literature, a discrepancy which may indicate that these stars pulsate aspherically.
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Based on complete light curves in the five channels of the Walraven VBLUW photometric system, a discussion is given of the determination of blanketing and reddening for RR Lyrae stars. A photometric accuracy of the order of 0.005 mag has been reached. Blanketing derived from the reddening-free color index /B-L/ is shown to be equivalent to other ways of determining the metallicity of RR Lyrae stars, such as delta (u-B)s, m1, and delta S. Two independent ways to find the interstellar-reddening correction are studied; they lead to identical results. A table is given with high-accuracy blanketing and reddening values for 73 RRab, 13 RRc, and a few short-period (RRs) variables. The relation between the present observations and those in other intermediate-band systems is considered.
Article
We derive the basic physical parameters of the field double-mode RR Lyrae star BS Com from its observed periods and the requirement of consistency between the pulsational and evolutionary constraints. By using the current solar-scaled horizontal branch evolutionary models of Pietrinferni et al. and our linear non-adiabatic purely radiative pulsational models, we get M/M⊙= 0.698 ± 0.004, log(L/L⊙) = 1.712 ± 0.005, Teff= 6840 ± 14 K, [Fe/H]=−1.67 ± 0.01, where the errors are standard deviations assuming uniform age distribution along the full range of uncertainty in age. The last two parameters are in a good agreement with the ones derived from the observed BVIC colours and the updated atlas9 stellar atmosphere models. We get Teff= 6842 ± 10 K, [Fe/H]=−1.58 ± 0.11, where the errors are purely statistical ones. It is remarkable that the derived parameters are nearly independent of stellar age at early evolutionary stages. Later stages, corresponding to the evolution towards the asymptotic giant branch, are most probably excluded because the required high temperatures are less likely to satisfy the constraints posed by the colours. We also show that our conclusions are only weakly sensitive to non-linear period shifts predicted by current hydrodynamical models.
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The behaviour of the spectral metallicity parameters ΔS of the RR Lyrae stars in the course of light change is considered. Electrophotometry results of 9 stars of the given class inUVbYβ are presented. Analysis of the data obtained shows that the variables for which variation of ΔS with the light phase was established do not show any real variations of metallicity indexm 1.
Article
The various observational arguments that can be or have been used to determine the nature of dwarf Cepheids are examined. Three evolutionary hypotheses are outlined and shown to lead to different expected period changes. Despite careful analysis, the derived period changes do not provide definite information on the evolutionary stage of most of the stars examined. Evidence for the Population I nature of most dwarf Cepheids (which are normal delta Scuti stars with large amplitudes) is presented.
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Ten RR Lyr stars have been observed at different pulsational phases with Caby photoelectric photometry to calibrate the response of this system to RR Lyr metallicity. As has been done for nonvariable stars, the data are displayed in a color-color diagram of hk vs b-y, where hk=(Ca-b)-(b-y). It is found that the system is much more sensitive to metal abundance than the Stromgren m1 index, and that the system retains good sensitivity even at the hottest phases of pulsation. The data produce lines of constant metallicity on the hk/b-y diagram which are single valued with respect to both b-y and hk. Therefore Caby photometry gives a metallicity which is independent of pulsational phase, a distinct advantage over ΔS and other techniques used to find RR Lyr abundances. This phase independence probably arises from the fact that Caby photometry is concerned largely with total absorption from the Ca K and H lines and the b - y continuum, and not the specific shapes of the hydrogen lines, which can be affected by changes in surface gravity as a function of phase in the pulsation and by emission near maximum light. The metallicity of the RRc star V7S3 Cen is determined to be -0.69±0.2 dex using the Caby technique.
Article
VY Serpentis is one of the brighter field RR Lyrae variable stars of type ab. A high-dispersion spectrogram of VY Ser has been obtained and analyzed. The present investigation has the objective to estimate the metallicity and gravity of the star for use in an analysis. Estimates of both metallicity and gravity may be obtained by photometric means, but corroborating data are always desirable. The results will be used to convert photometric colors to temperatures and bolometric corrections. Attention is given to observations, reddening, model atmosphere calculations, line data, microturbulence and gravity. Photometric gravities and derived elemental abundances are presented in tables. It is found that VY Ser is a metal-poor star. It is a very cool variable, near the red edge of the instability strip, which may explain its large microturbulent velocity of 4.2 km/sec.
Article
Non-linear calculations of intermediate amplitude to investigate stability have been carried out for one hundred RR Lyrae models of varying composition, mass, luminosity, and effective temperature. Of these, the calculations have been extended to the maximum amplitude for fifty models. The dependence of the location of the instability strip on composition, mass, and luminosity has been explored. In particular, the high-temperature boundary of the strip increases by 500° K for each 15 per cent increase in the mass fraction of helium. The dependence on effective temperature of the phase shift, the ratio of radius and luminosity amplitudes, and the shape of the light-curve has been explored, and the correlations of these three measures have been found. These measures may then be applied to observed variables to determine their location in the instability strip and the helium content of their envelopes. The examples studied give best agreement at about 30 per cent helium by mass. The calculations reveal many details of the shapes of the light- and velocity-curves which may be compared to observation. A number of features of these curves of known variables are discussed, and the underlying explanation is investigated. The sources of the driving energy of these models have been explored. In the models of the most favored composition, 30 per cent helium, the hydrogen ionization region is almost as important to the driving as is the He II ionization. The effects that cause the amplitude to cease growing and level off at the observed maximum amplitude are explored: they appear to involve several non-linear effects, particularly a steep velocity front, in the He II ionization zone. A new kind of period-luminosity relation has been discovered. The shortest period at which the fundamental mode persists, before it changes to the first harmonic, has been found to be independent of mass and composition and to depend only on the luminosity. This relation was found to be P tr = 0 057 (L/L☉) 0.6 days. This has been used to interpret the varying period distributions of RR Lyrae stars in clusters and in the field with the result that the luminosities are found to vary from M bol = 0.57 for very metal-weak clusters to M bol = 0.96 for clusters only slightly weak in metals. Metal-rich variables are slightly less luminous still. These results lead to the conclusion that the masses of RR Lyrae stars are near 0.5 M☉, which must imply a significant mass loss. These conclusions appear to be consistent with the possible interior models.
Article
A powerful approach to the understanding of any group of stars is the study of any companion stars which can be shown to be physically connected. But RR Lyrae variables, in common with other members of Population II are deficient in physical pairs. Baize’s catalogue of variables with companions contains only one: CSV 1795 = ADS 9354 A. As far as can be determined no period or light curve has been published for this star and it remains doubtful whether it is an RR Lyrae variable.
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The RR Lyrae type variable HD 16456 has been discovered by the author in a spectroscopic and photometric survey of prospective high velocity stars. It has a period of 0.311331 days and an amplitude in V of 0.55 mag from 8.76 to 9.31. It is the second brightest known c-type variable; the rising branch occupies 0.47 of the period. It is a Population II star with only moderate metal deficiency.
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Recommended for spectrographic and photoelectric observations are the two variables of Beta Lyrae type, EP Lyrae and HP Lyrae. Both objects have been formerly classified as RV Tauri type stars according to their periods when no spectrographic observations were available. Objective prism plates taken with the Sonneberg 50/70/172 cm Schmidt telescope revealed the early supergiant spectral types of both stars.
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It is suggested, on the basis of four new variables, that there is more evidence for the presence of ultrashort-period cepheids than of close binaries among the blue stragglers of the old disk population and that the hypothesis which links the existence of stragglers with the interaction of the components of close binaries may need re-examination. The possibility that one of the newly discovered variables, HD 100366, and the known, large-amplitude ultrashort -period SX Phoenicis are blue stragglers in the halo population is discussed.
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An examination of the nine small-amplitude, ultrashort-period variables assigned to the Hyades group, including one newly discovered (HR 3588), shows that they are divided into two luminosity groups with no apparent period-luminosity relation. A search for similar stars in the old disk population revealed one (HD 6870) new variable in the σ Puppis group. It is concluded from the space motions and, in a few cases, membership in stellar groups that ultrashort-period variables of all amplitudes occur in both the young and old disk populations and there is no strong argument that they, as well as the other blue stragglers in the old disk population, are not stars of 1.5 to 2.5 ⵙ, in the shell hydrogen-burning stage of their evolution.
Article
Two-colour (B, V) photometry for 21 RR Lyrae variables in the globular cluster NGC 6981 is presented. Only one of the variables studied is of Bailey c-type. The light and colour curves are derived and correlations between some of their parameters are discussed and compared with those of other globular clusters. A mean mass of ~ 0.4 ℳ⊙ and a helium abundance of Y≳30 per cent are derived by comparison of the observations with pulsation theory.
Article
NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. For the brightest galaxy in each of 48 nearby clusters and 7 groups of galaxies, photoelectric measurements of V and V-r magnitudes have been made. Redshifts have been measured for those 39 clusters and 3 groups which did not have previously published redshifts. Absolute magnitudes and colors were calculated for each cluster, and the cscb dependence of the absolute magnitudes and colors was attributed to galactic absorption. After correcting for selection effects, the ratio of total to selective absorption was found to be [...]=3.9 which is consistent with [...]=3.0. The values found for the color-excess and absorption at the galactic pole are [...]=0.016 and [...]=0.06. This value for the color-excess is in agreement with [...]=0.03 found by Sturch for the RR Lyrae stars.