We analyse Galactic, Large Magellanic Cloud and Small Magellanic Cloud Cepheids and RR Lyrae variables in terms of period–colour (PC) and amplitude–colour (AC) diagrams at the phases of maximum and ...minimum light. We compiled Galactic Cepheids V- and I-band data from the literature. We make use of optical bands light-curve data from OGLE-III survey for Cepheids and RR Lyrae variables in the Magellanic Clouds. We apply the F-statistical test to check the significance of any variation in the slope of PC and AC relations for Cepheid variables. The PC relation at maximum light for Galactic Cepheids with periods longer than about 7 d is shallow and the corresponding AC relation is flat for the entire period range. For the fundamental mode Cepheids in the Magellanic Clouds, we find significant breaks in the PC and AC relations at both maximum and minimum light for periods around 10 d. The PC relation at maximum light for the Magellanic Clouds is flat for Cepheids with periods greater than 10 d. First overtone Cepheids with periods less than 2.5 d have a shallow PC relation at minimum light. For fundamental mode RR Lyraes, we confirm earlier work supporting a flat PC relation at minimum light and a significant relation between amplitude and colour at maximum light. We find that no such relations exist for first overtone RR Lyrae stars. These findings are in agreement with stellar photosphere/hydrogen ionization front interaction considerations. These non-linearities can provide strong constraints for models of stellar pulsation and evolution.
We present multiband Period–Luminosity (PL) relations for first-overtone mode Cepheids in the Small Magellanic Cloud (SMC). We derive optical band PL relations and the Wesenheit function using VI ...mean magnitudes from the Optical Gravitational Lensing Experiment (OGLE-III) survey. We cross-match OGLE-III first-overtone mode Cepheids to the 2MASS and SAGE-SMC catalogues to derive PL relations at near-infrared (JHK
s
) and mid-infrared (3.6 and 4.5 μm) wavelengths. We test for possible non-linearities in these PL relations using robust statistical tests and find a significant break only in the optical band PL relations at 2.5 d for first-overtone mode Cepheids. We do not find statistical evidence for a non-linearity in these PL relations at 1 d. The multiband PL relations for fundamental-mode Cepheids in the SMC also exhibit a break at 2.5 d. We suggest that the period break around 2.5 d is related to sharp changes in the light-curve parameters for SMC Cepheids. We also derive new optical and mid-infrared band PL relations for first-overtone mode Cepheids in the Large Magellanic Cloud (LMC). We compare multiband PL relations for first-overtone mode Cepheids in the Magellanic Clouds and find a significant difference in the slope of the V-band PL relations but not for I-band PL relations. The slope of PL relations are found to be consistent in most of the infrared bands. A relative distance modulus of Δμ = 0.49 ± 0.02 mag between the two clouds is estimated using multiband PL relations for the first-overtone mode Cepheids in the SMC and LMC.
We present a detailed statistical analysis of possible non-linearities in the period-luminosity (PL), period-Wesenheit (PW) and period-colour (PC) relations for Cepheid variables in the Large ...Magellanic Cloud (LMC) at optical (VI) and near-infrared (JHKs) wavelengths. We test for the presence of possible non-linearities and determine their statistical significance by applying a variety of robust statistical tests (F-test, random-walk, testimator and the Davies test) to optical data from third phase of the Optical Gravitational Lensing Experiment and near-infrared data from Large Magellanic Cloud Near-Infrared Synoptic Survey. For fundamental-mode Cepheids, we find that the optical PL, PW and PC relations are non-linear at 10 d. The near-infrared PL and the ... relations are non-linear around 18 d; this break is attributed to a distinct variation in mean Fourier amplitude parameters near this period for longer wavelengths as compared to optical bands. The near-infrared PW relations are also non-linear except for the ... relation. For first-overtone mode Cepheids, a significant change in the slope of PL, PW and PC relations is found around 2.5 d only at optical wavelengths. We determine a global slope of -3.212 plus or minus 0.013 for the ... relation by combining our LMC data with observations of Cepheids in Supernovae host galaxies. We find this slope to be consistent with the corresponding LMC relation at short periods, and significantly different to the long-period value. We do not find any significant difference in the slope of the global-fit solution using a linear or non-linear LMC PL relation as calibrator, but the linear version provides a two times better constraint on the slope and metallicity coefficient. (ProQuest: ... denotes formulae/symbols omitted.)
ABSTRACT
This is the second of a series related to the study of geometry of the Magellanic Clouds based on multiwavelength photometry of classical Cepheids. In this paper we determine the geometrical ...and viewing angle parameters of the Small Magellanic Cloud (SMC) using the Leavitt law for classical Cepheids with/without a break in the law at a certain period as reported in the literature. The study utilizes photometric data for more than 3400 common classical Cepheids (Fundamental (FU) and First overtone (FO)) in optical (V, I), near-infrared (Y, J, Ks) and mid-infrared (3.6 and 4.5 μm) photometric bands. We obtain statistical reddening and distance modulus free from the effect of reddening to each of the individual Cepheids with respect to the mean distance modulus and reddening of the SMC. The reddening maps of the SMC obtained from the analyses with/without breaks in the Leavitt law show good agreement with each other as well as with other maps available in the literature. The Cartesian coordinates of individual stars with respect to the galaxy plane are obtained using the information of equatorial coordinates (α, δ) as well as extinction-free distance measurements. Modelling the observed 3D distribution of the Cepheids as a triaxial ellipsoid, we obtain the geometrical and viewing angle parameters of the SMC. The weighted average yields the following values of parameters for the SMC: the geometrical axes ratios of 1.000 ± 0.001: 1.544 ± 0.002: 9.742 ± 0.030 and the viewing angle parameters having inclination angle i = 3${^{\circ}_{.}}$465 ± 0${^{\circ}_{.}}$030 with respect to the longest axis from the line of sight and position angle of line of nodes (major axis) θlon = 63${^{\circ}_{.}}$086 ± 0${^{\circ}_{.}}$117.
ABSTRACT Investigation of period-color (PC) and amplitude-color (AC) relations at the maximum and minimum light can be used to probe the interaction of the hydrogen ionization front (HIF) with the ...photosphere and the radiation hydrodynamics of the outer envelopes of Cepheids and RR Lyraes. For example, theoretical calculations indicated that such interactions would occur at minimum light for RR Lyrae and result in a flatter PC relation. In the past, the PC and AC relations have been investigated by using either the (V − R)MACHO or (V − I) colors. In this work, we extend previous work to other bands by analyzing the RR Lyraes in the Sloan Digital Sky Survey Stripe 82 Region. Multi-epoch data are available for RR Lyraes located within the footprint of the Stripe 82 Region in five (ugriz) bands. We present the PC and AC relations at maximum and minimum light in four colors: (u − g)0, (g − r)0, (r − i)0, and (i − z)0, after they are corrected for extinction. We found that the PC and AC relations for this sample of RR Lyraes show a complex nature in the form of flat, linear or quadratic relations. Furthermore, the PC relations at minimum light for fundamental mode RR Lyrae stars are separated according to the Oosterhoff type, especially in the (g − r)0 and (r − i)0 colors. If only considering the results from linear regressions, our results are quantitatively consistent with the theory of HIF-photosphere interaction for both fundamental and first overtone RR Lyraes.
In this work, we updated the catalog of Galactic Cepheids with 24 mu m photometry by cross-matching the positions of known Galactic Cepheids to the recently released MIPSGAL point source catalog. We ...have added 36 new sources featuring MIPSGAL photometry in our analysis, thus increasing the existing sample to 65. Six different sources of compiled Cepheid distances were used to establish a 24 mu m period-luminosity (P-L) relation. Our recommended 24 mu m P-L relation is M sub(24 mu m) = -3.18(+ or -0.10))log P - 2.46(+ or -0.10), with an estimated intrinsic dispersion of 0.20 mag, and is derived from 58 Cepheids exhibiting distances based on a calibrated Wesenheit function. The slopes of the P-L relations were steepest when tied solely to the 10 Cepheids exhibiting trigonometric parallaxes from the Hubble Space Telescope and Hipparcos. Statistical tests suggest that these P-L relations are significantly different from those associated with other methods of distance determination, and simulations indicate that difference may arise from the small sample size.
This work presents the study of multiphase relations of classical Cepheids in the Magellanic Clouds for short periods (log P < 1) and long periods (log P > 1). From the analysis, it has been found ...that the multiphase relations obtained using the models as well as observations are highly dynamic with pulsational phase. The multiphase relations for short and long periods are found to display contrasting behaviour for both LMC and SMC. It has been observed that the multiphase relations obtained using the models agree better with the observations in the PC plane in most phases in comparison to the PL plane. Multiphase relations obtained using the models display a clear distinction among different convection sets in most phases. Comparison of models and observations in the multiphase plane is one way to test the models with the observations and to constrain the theory of stellar pulsation.
In this paper, we have derived Cepheid period-luminosity (P-L) relations for the Large Magellanic Cloud (LMC) fundamental mode Cepheids, based on the data released from OGLE-III. We have applied an ...extinction map to correct for the extinction of these Cepheids. In addition to the VIW-band P-L relations, we also include JHK and four Spitzer IRAC-band P-L relations, derived by matching the OGLE-III Cepheids to the Two Micron All Sky Survey and SAGE data sets, respectively. We also test the nonlinearity of the Cepheid P-L relations based on extinction-corrected data. Our results (again) show that the LMC P-L relations are nonlinear in VIJH bands and linear in KW and the four IRAC bands, respectively.
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