33 research outputs found
Synthetic Population of Binary Cepheids. II. The effect of companion light on the extragalactic distance scale
Because of their period-luminosity relation (PLR), classical Cepheids play a
key role in the calibration of the extragalactic distance scale and the
determination of the Hubble-Lema\^{i}tre constant . Recent findings show
that the majority of classical Cepheids should be in binary or multiple
systems, which might undermine their accuracy, as the extra -- and unaccounted
for -- light from the companions of Cepheids causes a shift in the PLR. We
quantify this shift using synthetic populations of binary Cepheids that we
developed for this purpose, as described in Paper I of this series. We find
that while all PLRs are shifted toward brighter values due to the excess light
from the companions, the bias in the relative distance modulus between two
galaxies hosting binary Cepheids can be either positive or negative, depending
on the percentage of binary Cepheids in them. If the binarity percentage in the
two galaxies is similar, the effect of binarity is canceled. Otherwise, it
introduces a shift in the distance modulus of the order of millimags in the
near-infrared passbands and Wesenheit indices, and tens of millimags in the
visual domain; its exact value depends on the variant of the synthetic
population (a unique combination of metallicity, star formation history, shape
and location of the instability strip, and initial parameter distributions).
Such shifts in distance moduli to type Ia supernova host galaxies introduce an
additional statistical error on , which however does not prevent measuring
with a precision of 1%.Comment: 16 pages, 11 figures, accepted for publication in The Astrophysical
Journa
Synthetic population of binary Cepheids. I. The effect of metallicity and initial parameter distribution on characteristics of Cepheids' companions
The majority of classical Cepheids are binary stars, yet the contribution of
companions' light to the total brightness of the system has been assumed
negligible and lacked a thorough, quantitative evaluation. We present an
extensive study of synthetic populations of binary Cepheids, that aims to
characterize Cepheids' companions (e.g. masses, evolutionary and spectral
types), quantify their contribution to the brightness and color of Cepheid
binaries, and assess the relevance of input parameters on the results. We
introduce a collection of synthetic populations, which vary in metal content,
initial parameter distribution, location of the instability strip edges, and
star formation history. Our synthetic populations are free from the selection
bias, while the percentage of Cepheid binaries is controlled by the binarity
parameter. We successfully reproduce recent theoretical and empirical results:
the percentage of binary Cepheids with main sequence (MS) companions, the
contrast-mass ratio relation for binary Cepheids with MS companions, the
appearance of binary Cepheids with giant evolved companions as outlier data
points above the period-luminosity relation. Moreover, we present the first
estimation of the percentage of binary Cepheids in the Large Magellanic Cloud
and announce the quantification of the effect of binarity on the slope and
zero-point of multiband period-luminosity relations, which will be reported in
the next paper of this series.Comment: 29 pages, 19 figures (5 in the Appendix), accepted for Ap
Studies of RR Lyrae Variables in Binary Systems. I. Evidence of a Trimodal Companion Mass Distribution
We present 87 candidates for RR Lyrae variable stars in binary systems, based on our new search using the light-travel time effect (LTTE) and observed - calculated (O - C) diagrams in the Galactic bulge time-series photometry of the Optical Gravitational Lensing Experiment. Out of these, 61 are new candidates, while 26 have been announced previously. Furthermore, 12 stars considered as binary candidates in earlier works are discarded from the list, either because they were found to have O - C diagrams incompatible with the LTTE or because their long-term periodicity is definitely caused by the Blazhko effect. This sample of RR Lyrae binary candidates allows us to draw the first firm conclusions about the population of such objects: no candidate has an orbital period below 1000 days, while their occurrence rate steadily increases with increasing period, and peaks between 3000 and 4000 days; however, the decrease in the number of stars toward even longer periods is probably the result of observational biases. The eccentricities show a very significant concentration between 0.25 and 0.3, with a quarter of candidates found in this single bin, overlaid on an otherwise flat distribution between 0.05 and 0.6. Only six stars have inferred eccentricities above 0.6. Lastly, the distribution of the mass functions is highly peculiar, exhibiting strong trimodality. We interpret these modes as the presence of three distinct groups of companions, with typical inferred masses of similar to 0.6, similar to 0.2, and similar to 0.067 M (circle dot), which can be associated with populations of white dwarf and main sequence, red dwarf, and brown dwarf companions, respectively
Period-Luminosity Relations for Galactic classical Cepheids in the Sloan bands
We present the first period-luminosity (PL) and period-Wesenheit (PW)
relations in the Sloan-Pans-STARRS gP1rP1iP1 bands for classical fundamental
mode Cepheids in the Milky Way. We used a relatively modest number of 76 stars
for the PL and 84-85 stars for the PW relations calibration. The data for the
project were collected with the network of 40-cm telescopes of Las Cumbres
Observatory, and Gaia Data Release 3 parallaxes were used for the calculations.
These gri-band PL and PW relations calibrations will be a useful tool for
distance determinations in the era of large sky surveys using the Sloan
photometric system, especially with the near-future start of the Large Synoptic
Survey of Space and Time (LSST).Comment: 31 pages, 7 figures, 3 tables, Accepted for publication in Ap
The Araucaria Project. The distance to the Small Magellanic Cloud from late-type eclipsing binaries
We present a distance determination to the Small Magellanic Cloud (SMC) based
on an analysis of four detached, long period, late type eclipsing binaries
discovered by the OGLE Survey. The components of the binaries show negligible
intrinsic variability. A consistent set of stellar parameters was derived with
low statistical and systematic uncertainty. The absolute dimensions of the
stars are calculated with a precision of better than 3%.
The surface brightness - infrared color relation was used to derive the
distance to each binary. The four systems clump around a distance modulus of (m
- M)=18.99 with a dispersion of only 0.05 mag. Combining these results with the
distance published by Graczyk et al. for the eclipsing binary OGLE SMC113.3
4007 we obtain a mean distance modulus to the SMC of 18.965 +/- 0.025 (stat.)
+/- 0.048 (syst.) mag. This corresponds to a distance of 62.1 +/- 1.9 kpc,
where the error includes both uncertainties. Taking into account other recent
published determinations of the SMC distance we calculated the distance modulus
difference between the SMC and the LMC equal to 0.458 +/- 0.068 mag. Finally we
advocate mu_{SMC}=18.95 +/- 0.07 as a new "canonical" value of the distance
modulus to this galaxy.Comment: Accepted for publication in Ap
The Araucaria Project: A study of the classical Cepheid in the eclipsing binary system OGLE LMC562.05.9009 in the Large Magellanic Cloud
We present a detailed study of the classical Cepheid in the double-lined,
highly eccentric eclipsing binary system OGLE-LMC562.05.9009. The Cepheid is a
fundamental mode pulsator with a period of 2.988 days. The orbital period of
the system is 1550 days. Using spectroscopic data from three 4-8-m telescopes
and photometry spanning 22 years, we were able to derive the dynamical masses
and radii of both stars with exquisite accuracy. Both stars in the system are
very similar in mass, radius and color, but the companion is a stable,
non-pulsating star. The Cepheid is slightly more massive and bigger (M_1 = 3.70
+/- 0.03M_sun, R_1 = 28.6 +/- 0.2R_sun) than its companion (M_2 = 3.60 +/-
0.03M_sun, R_2 = 26.6 +/- 0.2R_sun). Within the observational uncertainties
both stars have the same effective temperature of 6030 +/- 150K. Evolutionary
tracks place both stars inside the classical Cepheid instability strip, but it
is likely that future improved temperature estimates will move the stable giant
companion just beyond the red edge of the instability strip. Within current
observational and theoretical uncertainties, both stars fit on a 205 Myr
isochrone arguing for their common age. From our model, we determine a value of
the projection factor of p = 1.37 +/- 0.07 for the Cepheid in the
OGLE-LMC562.05.9009 system. This is the second Cepheid for which we could
measure its p-factor with high precision directly from the analysis of an
eclipsing binary system, which represents an important contribution towards a
better calibration of Baade-Wesselink methods of distance determination for
Cepheids.Comment: Accepted to be published in Ap