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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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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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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.