PLC Relations Research Articles

Period–Luminosity–Metallicity–Color Relations of Late-type Contact Binaries in the Big Data Era

Binary stars ubiquitous throughout the Universe are important. Contact binaries (CBs) possessing period–luminosity (PL) relations could be adopted as distance tracers. The PL relations of CBs are influenced by metallicity abundance and color index, which are connected to both the radius and luminosity of stars. Here we propose fine relations of the period–luminosity–metallicity–color (PLZC) from the ultraviolet to infrared bands based on current surveys. The accuracy of the distance estimation is 6% and 8%, respectively, depending on the PLZC relations of the CBs in the infrared and optical bands of the collected data. PLZC models are still more accurate than PLC models in determining intrinsic luminosity, notwithstanding their limited improvement. Meanwhile, these relations based on synthetic photometry are also calibrated. On the basis of the synthetic photometry, a 6% accuracy of distance is estimated. The measured or synthetic data of PLZC or PLC relations in infrared bands comes first in the list of suggestions for distance estimations and is followed by the measured data of optical bands.

Establishing binarity amongst Galactic RV Tauri stars with a disc

This study is a contribution in comprehending the role of binarity upon late stages of stellar evolution. We determine the binary status of six Galactic RV Tauri stars, namely DY Ori, EP Lyr, HP Lyr, IRAS 17038-4815, IRAS 09144-4933 and TW Cam, which are surrounded by a dusty disc. We also place them on the HR diagram, thereby establishing their evolutionary nature. All the six Galactic RV Tauri stars included in this study are binaries with orbital periods ranging between $\sim$ 650 and 1700 days and with eccentricities between 0.2 and 0.6. The mass functions range between 0.08 to 0.55 M$_\odot$ which points to an unevolved low mass companion. In the photometric time series we detect a long-term variation on the time-scale of the orbital period for IRAS 17038-4815, IRAS 09144-4933 and TW Cam. Our derived stellar luminosities obtained from a calibrated PLC relation indicates that all except DY Ori and EP Lyr, are post-AGB stars. DY Ori and EP Lyr are likely examples of the recently discovered dusty post-RGB stars. The orbital parameters strongly suggest that the evolution of these stars was interrupted by a strong phase of binary interaction during or even prior to the AGB. The observed eccentricities and long orbital periods among these stars provides a challenge to the standard theory of binary evolution.

Study of globular cluster M53: new variables, distance, metallicity

We study the variable star content of the globular cluster M53 to compute the physical parameters of the constituting stars and the distance of the cluster. Covering two adjacent seasons in 2007 and 2008, new photometric data are gathered for 3048 objects in the field of M53. By using the OIS method and subsequently TFA, we search for variables in the full sample by using DFT and BLS methods. We select variables based on the statistics related to these methods combined with visual inspections. We identified 12 new variables (2 RR Lyrae stars, 7 short periodic stars - 3 of them are SX Phe stars - and 3 long-period variables). No eclipsing binaries were found in the present sample. Except for the 3 (hitherto unknown) Blazhko RR Lyrae stars, no multiperiodic variables were found. We showed that after proper period shift, the PLC relation for the first overtone RR Lyrae sample tightly follows the one spanned by the fundamental stars. Furthermore, the slope is in agreement with the one derived from other clusters. Based on the earlier Baade-Wesselink calibration of the PLC relations, the derived reddening-free distance modulus of M53 is 16.31 +/- 0.04 mag, corresponding to a distance modulus of 18.5 mag for the Large Magellanic Cloud. From the Fourier parameters of the RRab stars we obtained an average iron abundance of -1.58 +/- 0.03. This is ~0.5 dex higher than the overall abundance of the giants as given in the literature and derived in this paper from the three-color photometry of giants. We suspect that the source of this discrepancy (observable also in other, low-metallicity clusters) is the want of sufficient number of low-metallicity objects in the calibrating sample of the Fourier method.

The extragalactic Cepheid bias: a new test using the period-luminosity-color relation

We use the Period-Luminosity-Color relation (PLC) for Cepheids to test for the existence of a bias in extragalactic distances derived from the classical Period-Luminosity (PL) relation. We calculate the parameters of the PLC using several galaxies observed with the Hubble Space Telescope and show that this calculation must be conducted with a PLC written in a form where the parameters are independent. The coefficients thus obtained are similar to those derived from theoretical models. Calibrating with a few unbiased galaxies, we apply this PLC to all galaxies of the Hubble Space Telescope Key Program (HSTKP) and compare the distance moduli with those published by the HSTKP team. The new distance moduli are larger (more exactly, the larger the distance the larger the difference), consistent with a bias. Further, the bias trend that is observed is the same previously obtained from two independent methods based either on the local Hubble law or on a theoretical model of the bias. The results are quite stable but when we force the PLC relation closer to the classical PL relation by using unrealistic parameters, the agreement with HSTKP distance moduli is retrieved. This also suggests that the PL relation leads to biased distance moduli. The new distance moduli reduce the scatter in the calibration of the absolute magnitude of supernovae SNIa at their maximum. This may also suggest that the relation between the amplitude at maximum and the decay of the light curve Δm 15 may not be as strong as believed.

New Cepheid Period-Luminosity Relations for the Large Magellanic Cloud: 92 Near-Infrared Light Curves

Near-infrared J, H, and Ks photometric measurements of 92 Cepheids in the Large Magellanic Cloud are presented. The stars are spread over the face of the Cloud, their periods range from 3 to 100 days, and their light curves are sampled at an average of 22 phase points per star. The intensity-weighted mean magnitudes and colors define period-luminosity-color (PL or PLC) relations whose uncertainties due to differential metal abundance and reddening/extinction effects are minimal. The dispersions in the infrared PL, PLC, and extinction-free period-Wesenheit relations are extremely small, amounting to less than 0.10 mag (or 5% in distance). The orientation of the disk plane of the sample (inclination angle and line of nodes) agrees well with the 2001 results of van der Marel & Cioni. The PL and PLC fits are the best-determined such relationships yet found for any sample of Cepheids and establish a calibration that can be used to precisely anchor ground- and space-based near-infrared Cepheid data to external galaxies, as well as back to Cepheid calibrators in the Galaxy. As an example, we use the 1998 Galactic Cepheid calibration of Gieren and coworkers to obtain the distance modulus to the centroid of our LMC sample. The true modulus of the LMC is thus determined to be 18.50 ± 0.05 mag. Currently, the dominant source of uncertainty in this number is the scatter in the Galactic calibrator sample. The PLC fits and dispersions and the dependence of the PLC on metal abundance are compared with theoretical versions computed from the 1999 work of Alibert and coworkers. Overall, the agreement is excellent, indicating that at near-infrared wavelengths the slope and dispersion of the PLC depend very weakly on metal abundance. The shift in the JHK PLC relations is ~0.02 mag for a change in metal abundance from solar to one-half solar.

Theoretical Models for Classical Cepheids. IV. Mean Magnitudes and Colors and the Evaluation of Distance, Reddening, and Metallicity

We discuss the metallicity effect on the theoretical visual and near-infrared PL and PLC relations of classical Cepheids, as based on nonlinear, nonlocal and time--dependent convective pulsating models at varying chemical composition. In view of the two usual methods of averaging (magnitude-weighted and intensity-weighted) observed magnitudes and colors over the full pulsation cycle, we briefly discuss the differences between static and mean quantities. We show that the behavior of the synthetic mean magnitudes and colors fully reproduces the observed trend of Galactic Cepheids, supporting the validity of the model predictions. In the second part of the paper we show how the estimate of the mean reddening and true distance modulus of a galaxy from Cepheid VK photometry depend on the adopted metal content, in the sense that larger metallicities drive the host galaxy to lower extinctions and distances. Conversely, self-consistent estimates of the Cepheid mean reddening, distance and metallicity may be derived if three-filter data are taken into account. By applying the theoretical PL and PLC relations to available BVK data of Cepheids in the Magellanic Clouds we eventually obtain Z \sim 0.008, E(B-V) \sim 0.02 mag, DM \sim 18.63 mag for LMC and Z \sim 0.004, E(B-V) \sim 0.01 mag., DM \sim 19.16 mag. for SMC. The discrepancy between such reddenings and the current values based on BVI data is briefly discussed.

Observations of Cepheid Variables in Two LMC Clusters Using EROS 2 Data

It is well known that Cepheid variables are very important distance indicators because of their PL and PLC relations. The distances derived through the quoted relations are affected by well known systematic effects, since, in general, we have a poor knowledge of both reddening and metallicity of the Cepheid sample. Good estimates of the quoted parameters can be achieved if the observed Cepheids are cluster members since, by comparison between cluster CMD and theoretical isochrones we can estimate the cluster reddening, metallicity and age, i.e., the evolving masses for each evolutionary phase. The ideal objects to be searched for Cepheid membership are Magellanic Cloud clusters since they are well populated in the relevant evolutionary phases.

Observations of Cepheid Variables in Two LMC Clusters Using EROS 2 Data

It is well known that Cepheid variables are very important distance indicators because of their PL and PLC relations. The distances derived through the quoted relations are affected by well known systematic effects, since, in general, we have a poor knowledge of both reddening and metallicity of the Cepheid sample. Good estimates of the quoted parameters can be achieved if the observed Cepheids are cluster members since, by comparison between cluster CMD and theoretical isochrones we can estimate the cluster reddening, metallicity and age, i.e., the evolving masses for each evolutionary phase. The ideal objects to be searched for Cepheid membership are Magellanic Cloud clusters since they are well populated in the relevant evolutionary phases.

On the Period-Luminosity-Color Relation of Classical Cepheids

We compare the theoretical and empirical PL relations in V and I bands for Cepheids in the LMC. We found that, within the current intrinsic dispersions, the theoretical predictions are in remarkable agreement with observational data. We also discuss the PLC relations in (V,B-V) and (V,V-I) as well as the dependence of distance determinations on uncertainties in colors, in reddening corrections and in metal content.

On the Period-Luminosity-Color Relation of Classical Cepheids

We compare the theoretical and empirical PL relations in V and I bands for Cepheids in the LMC. We found that, within the current intrinsic dispersions, the theoretical predictions are in remarkable agreement with observational data. We also discuss the PLC relations in (V,B-V) and (V,V-I) as well as the dependence of distance determinations on uncertainties in colors, in reddening corrections and in metal content.

Galactic kinematics of Cepheids from Hipparcos proper motions

The Hipparcos proper motions of 220 galactic Cepheids, together with relevant ground-based photometry, have been analysed. The effects of galactic rotation are very clearly seen. Mean values of the Oort constants, A = 14.82 +/- 0.84 km/s/kpc, and B = -12.37 +/- 0.64 km/s/kpc, and of the angular velocity of circular rotation at the Sun, Omega_0 = 27.19 +/- 0.87 km/s/kpc, are derived. Comparison of the value of A with values derived from recent radial velocity solutions confirm, within the errors, the zero-points of the PL and PLC relations derived directly from the Hipparcos trigonometrical parallaxes of the same stars. The proper motion results suggest that the galactic rotation curve is declining slowly at the solar distance from the galactic centre (dTheta/dR = -2.4 +/- 1.2 km/s/kpc). The component of the solar motion towards the North Galactic Pole is found to be +7.61 +/- 0.64 km/s. Based on the increased distance scale deduced in the present paper the distance to the galactic centre derived in a previous radial velocity study is increased to R_0 = 8.5 +/- 0.5 kpc.

Empirical Approach to Cepheid Period-Luminosity-Color and Period-Luminosity Relations by Surface Brightness

view Abstract Citations (16) References (41) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Empirical Approach to Cepheid Period-Luminosity-Color and Period-Luminosity Relations by Surface Brightness di Benedetto, G. P. Abstract Empirical period-luminosity-color and period-luminosity (PLC [V, B-V] and PL[V] relations according to Stefan's law are derived for Cepheid variables by applying thermal scales of nonvariable giant and supergiant stars established by modern observational interferometry. Intrinsic surface brightnesses are predicted by the apparent color index V - K as fiducial reference unbiased by metallicity and gravity effects, along with current optical absorption data. Linear radii are inferred from periods through the period-radius relation, assumed to be insensitive to abundance and brightness variations. The dependence of PLC and PL zero points to abundance effects is further investigated. I compare current Cepheid data from our metal- normal Galaxy (GAL) with those in the Magellanic Clouds (LMC and SMC) of poorer metal content. The major achievement is that the PL(V) relations are found to be severely biased by metallicity, whereas the PLC(V, B- V) relations turn out to be much less affected by abundances than previously expected. The new PLC and PL relations calibrated on fundamental quantities are compared with those from the classical zero-age main-sequence (ZAMS) fitting empirical approach. It is shown that all metal-normal equations lead to remarkably consistent luminosities of GAL Cepheids, to within +/- 0.05 mag (PL) and +/- 0.02 mag (PLC), whereas metal-poor LMC and SMC results appear to be significantly discrepant. It is emphasized that theoretical thermal scales applied for the derivation of ZAMS metal- corrected relations, either explicit or implicit, are mainly responsible for such observed discrepancies. The actual empirical approach appears to overcome most of the previous difficulties closely related to the poor knowledge of Cepheid thermal properties. Theoretical Cepheid thermal scales are critically reviewed. It is found that recent metal-normal color-brightness relations lead to results remarkably consistent with those from observational scales, whereas metal-poor predictions appear to be overestimated, at least for Cepheid periods log P (days) > 1 currently observed in extragalactic work. Theoretical PLC(V, B-V) and PL(V) relations revised according to unbiased conversion scales now support the above finding that PLC relations are less affected by metallicity than PL relations. This also enables the reconciliation of evolution, pulsation, and stellar atmosphere theories since the ratio of evolution to pulsation mass is found to be very close to 1 for all GAL, LMC, and SMC Cepheids. Because of the poorer metal content of the Magellanic Clouds, current PL( V) distance to the LMC and SMC are found to be underestimated, being referred to metal-normal GAL Cepheids as primary calibrators. Distance moduli through either infrared photometry (V, V - K) (pulsation parallaxes) or optical photometry (V, B- V) now become (m - M)_0_(LMC) = 18.64 +/- 0.02, (m - M)_0_(SMC) = 19.09 +/- 0.02. Publication: The Astrophysical Journal Pub Date: October 1995 DOI: 10.1086/176291 Bibcode: 1995ApJ...452..195D Keywords: GALAXIES: DISTANCES AND REDSHIFTS; GALAXIES: MAGELLANIC CLOUDS; STARS: ABUNDANCES; STARS: FUNDAMENTAL PARAMETERS; STARS: OSCILLATIONS; STARS: VARIABLES: CEPHEIDS full text sources ADS | data products SIMBAD (3) NED (2)

The Use of Maximum Light in Cepheid Distance Estimators

AbstractCepheid PLC relations are usually constructed using mean light. We show that the use of maximum and mean light leads to a distance estimator for the LMC with 30% less scatter than existing relations.

The binary system containing the classical Cepheid T MON

Several new results are presented for the binary system containing the 27(sup d) classical Cepheid T Mon. New radial velocities for the Cepheid have been obtained, which confirm the decreasing orbital motion at the current epoch. The spectral type of the companion (B9.8 V) has been determined from an International Ultraviolet Explorer (IUE) low resolution spectrum. An IUE high resolution spectrum has been measured to search for the velocity of the companion. A velocity signal at +36 km/s on JD 2,446,105.21 has been tentatively identified as the velocity of the companion, but confirmation of this velocity would be very valuable. Results based on this tentative identification of the velocity are that the companion does not have a high projected rotation velocity, that the companion is unlikely to be a short period binary, and that the gamma velocity of the system is between 20 and 36 km/s. The luminosity and temperature of both the Cepheid and the companion are well determined from the satellite and ground-based observations and the Cepheid PLC relation. However, the companion is above the ZAMS in the H-R diagram, which is inconsistent with the large luminosity difference between the two stars. High rotation for the companion (viewed pole-on) is a possible explanation. The lower limit to the mass function (from the lower limits to the orbital period and amplitude) requires a very high eccentricity for the system for reasonable estimates for the masses of the two stars.

Galactic clusters with associated Cepheid variables. 4: C2128+488 (Anon. Platais) and V1726 Cygni

view Abstract Citations (20) References (46) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Galactic Clusters With Associated Cepheid Variables. IV. C2128+488 (ANON. PLATAIS) And V1726 Cygni Turner, David G. ; Mandushev, Georgi I. ; Forbes, Douglas Abstract New photoelectric UBV photometry of 32 stars, photographic UBV photometry of 120 stars, and spectroscopic observations of 8 stars are presented for C 2128+488 (Anon. Platais), the cluster associated with the 4d.237 s-Cepheid V1726 Cygni. The resulting photometry, spectral classifications, and radial velocities are used with spectroscopic and proper motion data previously published by Platais and others for the Cepheid and other stars in this field in a detailed cluster analysis. The newly obtained cluster distance modulus is Vzero - MV = 10.98 +/- 0.02s.e. (d = 1568 +/- 13 pc), and a value of R = AV/EV-V = 3.07 +/- 0.27 s.e. is found to describe the dust extinction in the field. A space reddening of EB-V = 0.43 +/- 0.02 is derived for V1726 Cyg from two late B-type companions which bracket the Cepheid, as well as from the reddenings of other stars in the field. Its resulting luminosity as a probable cluster member is (MV) = -3.42 +/- 0.07. A cluster radial velocity of -15.4 +/-0.2 km/sec and a cluster turnoff point at spectral type B7 are both consistent with the likely membership of V1726 Cyg, as are the available proper motion data. The small amplitude, sinusoidal light curve, and location of V1726 Cyg on the blue edge of the Cepheid instability strip are consistent with the properties expected for overtone pulsation, although such a possibility appears to imply an unrealistically small value (beta = 0.5 +/- 0.2) for the color coefficient in the PLC relation. A more reasonable value of beta = 2.1 +/- 0.2 is derived for the color term applicable to galactic cluster Cepheids in this program when V1726 Cyg is assumed to be pulsating in the fundamental mode. Publication: The Astronomical Journal Pub Date: May 1994 DOI: 10.1086/116988 Bibcode: 1994AJ....107.1796T Keywords: Astronomical Photometry; Cepheid Variables; Classifications; Color-Color Diagram; Color-Magnitude Diagram; Cygnus Constellation; Galactic Clusters; Spectroscopic Analysis; Astronomical Observatories; Electrophotometers; Optical Filters; Photographic Plates; Photographs; Photomultiplier Tubes; Radial Velocity; Telescopes; Astronomy; CEPHEIDS full text sources ADS | data products SIMBAD (160) GCPD (1) Related Materials (6) Part 1: 1986AJ.....92..111T Part 2: 1992AJ....104.1132T Part 3: 1992AJ....104.1865T Part 5: 1997AJ....113.2104T Part 6: 1998AJ....115.1958T Part 7: 2008MNRAS.388..444T

The Cepheid Period-Luminosity Relation from Independent Distances of 100 Galactic Variables

view Abstract Citations (86) References (78) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Cepheid Period-Luminosity Relation from Independent Distances of 100 Galactic Variables Gieren, Wolfgang P. ; Barnes, Thomas G., III ; Moffett, Thomas J. Abstract We have determined distances to 100 galactic classical Cepheids on a homogeneous system with an improved version of the surface brightness technique, using the extensive northern Cepheid observations of Moffett and Barnes, and the southern Cepheid observations of Gieren. The period-luminosity relations in the V bandpass obtained for the northern and southern Cepheid samples are found consistent, and the absolute magnitudes have been combined into a two-hemisphere PL(V) relation which is Mv= -1.371 -2.986 log P. ±0.095 ±0.094 This is the currently most precise Cepheid PL(V) relation from the surface brightness technique. Typically Mv can be obtained from this relation for Cepheids with periods in the range 3 to 45 days to better than ±0.06 mag, if all the scatter in the relation is observational, or ±0.27 mag, if all the scatter is cosmic in origin. We compare our result to other recent observational determinations of the PL(V) relation and find consistency among the results produced by the surface brightness method, main-sequence fitting of open clusters and associations containing Cepheids, Hβ photometry, and statistical parallaxes. In particular, there is no significant difference between the surface brightness and ZAMS-fitting Cepheid distance scales. The agreement between the ZAMS-fitting distance scale and the fully independent surface brightness distance scale provides extremely persuasive evidence that both methods are free of significant systematic errors at the ±0.10 mag level. We show that there is no significant correlation between the residuals of the Mv from the PL(V) relation and the residuals of the intrinsic (B - V) colors of the Cepheids from the mean period-color relation, making it impossible to find a PLC relation from our data. After correcting the Cepheid distances for the small, theoretically predicted metallicity dependence of the surface brightness technique, we find no significant trend in the Mv residuals from our PL(V) relation with the galactocentric distances of the Cepheids. While the Cepheids become intrinsically bluer as their radial distances from the Galactic center increase, their mean absolute magnitudes, at a given period, do not depend on their galactocentric distances at a significant level, which is an important property in view of the use of Cepheid variables as extragalactic distance indicators. Publication: The Astrophysical Journal Pub Date: November 1993 DOI: 10.1086/173377 Bibcode: 1993ApJ...418..135G Keywords: COSMOLOGY: DISTANCE SCALE; STARS: OSCILLATIONS; STARS: VARIABLES: CEPHEIDS full text sources ADS | data products SIMBAD (100) NED (1)

Long-period variables and carbon stars in the Galactic Bulge

The review covers the properties of red variables in globular clusters and the Galactic Bulge. Details are given of our current understanding of the Mira evolutionary phase. There is evidence that Miras in the LMC and the Bulge occupy different parts of the instability strip but obey the same PLC relation. The Bulge contains at least 2 × 104 Miras of which 100 or so have luminosities in excess of Mbol = — 5 mag. The Mira phase lasts more than 105 yr. These objects originate from stars with a wide range of metallicity, but it is currently unclear if the most metal-rich stars reach the top of the AGB to become Miras. Preliminary data suggest that the distribution of the Miras along the minor axis of the Bulge is different from that of the late-M stars but similar to the 2.4 μm luminosity.Our knowledge of the Bulge carbon stars is briefly reviewed. It is suggested that, by analogy with the carbon-rich dwarfs, these stars are probably best understood as the products of binary evolution.

Absolute magnitudes and kinematic properties of Cepheids

A maximum likelihood statistical parallax analysis of classical Cepheids has been performed to determine the relative solar motion, Oort constants, velocity ellipsoid parameters, and zero points of the PL and PLC relations. The analysis is based upon 90 proper motions drawn from the list of Karimova and Pavlovskaya and upon the analytical approach of Hawley et al. Our results give a best estimate for the mean absolute magnitude of Cepheids at log P=0.8 of =−3.46±0.33 mag. This estimate for the Cepheid absolute magnitude zero point is highly stable against refinements in the mathematical technique and against additional Cepheid proper motion data of quality similar to the existing proper motions

A period-luminosity-colour relation for Mira variables

Time-averaged J, H, K and mbol magnitudes are given for 29 O-rich and 20 C-rich Mira variables in the Large Magellanic Cloud. PL and PC relations are derived. The PL relations for O-Miras and C-Miras are very similar at K. For the O-Miras the residuals from the PL and PC relations are correlated showing the existence of PLC relations. Such relations are derived and compared with the theoretical pulsation equation. Data are also given for six variables with periods greater than 420 d. These are brighter by 0.7 mag than expected from extrapolations of the PL or PLC relations. Using Miras in galactic globular clusters to estimate the cluster distances (from the PLC relation) gives a mean horizontal branch luminosity of + 0.71 ± 0.09 (internal standard error) at [Fe/H] = − 0.58, in good agreement with that derived in other ways. For the C-Miras, a significant color term is estimated for the PLC relation at J. There is, however, little evidence for a significant color term at K and the evidence for one in mbol is marginal.

SPECTROSCOPIC OBSERVATIONS OF YELLOW SUPERGIANTS: I. RADIAL PULSATIONS OF RHO CASSIOPEIAE.

ABSTRACT High-resolution Reticon spectra of the F8 Ia-0 supergiant ρ Cas providing lines of differing excitation potential are employed to construct radial-velocity curves which reveal a semiregular pulsation of the atmosphere. Analysis of line-doubling episodes supports the presence of a dominant radial pulsation mode with a period around 500 days, significantly longer than the radial fundamental mode predicted on the basis of Cepheid-like PLC relations for a star evolving to the red supergiant region. Predicted periods for fundamental radial pulsations in stars returning toward the blue supergiant region are comparable to the observed quasi-period.