40 research outputs found
The dynamical mass and evolutionary status of the type-II Cepheid in the eclipsing binary system OGLE-LMC-T2CEP-211 with a double-ring disk
We present the analysis of a peculiar W~Virginis (pWVir) type-II Cepheid,
OGLE-LMC-T2CEP-211 (), in a double-lined binary system
(), which shed light on virtually unknown evolutionary status
and structure of pWVir stars. The dynamical mass of the Cepheid (first ever for
a type-II Cepheid) is and the radius
. The companion is a massive ()
main-sequence star obscured by a disk. Such configuration suggests a mass
transfer in the system history. We found that originally the system
() was composed of and stars, with
the current Cepheid being more massive. The system age is now 200 My,
and the Cepheid is almost completely stripped of hydrogen, with helium mass of
of the total mass. It finished transferring the mass 2.5 My ago
and is evolving towards lower temperatures passing through the instability
strip. Comparison with observations indicate a reasonable
mass loss from the Cepheid. The companion is
most probably a Be main-sequence star with and .
Our results yield a good agreement with a pulsation theory model for a
hydrogen-deficient pulsator, confirming the described evolutionary scenario. We
detected a two-ring disk () and a shell
() around the companion, that is probably a
combination of the matter from the past mass transfer, the mass being lost by
the Cepheid due to wind and pulsations, and a decretion disk around a rapidly
rotating secondary. Our study together with observational properties of pWVir
stars suggests that their majority are products of a similar binary evolution
interaction.Comment: 21 pages, 14 figures, 6 tables, accepted for publication in Ap
Araucaria Project: Pulsating stars in binary systems and as distance indicators
Pulsating stars, like Cepheids or RR Lyrae stars, are ones of the most important distance indicators. They are also key objects for testing the predictions of stellar evolution and stellar pulsation theory. In the Araucaria Project we have studied these objects since 2002, measuring distances to the galaxies in the Local Group and beyond.
In 2010 we have for the first time confirmed spectroscopically the existence of a classical Cepheid in an eclipsing binary system. This has opened an opportunity to study in great details and with high accuracy (better than 1%) the physical parameters of these very important objects. First dynamical mass determination (Mcep = 4.16 ± 0.03 M⊙) let us solve the long-standing mass discrepancy problem. Since then we have measured masses for 6 classical Cepheids in binary systems and determined projection factors for three of them. One of the analyzed systems was confirmed to consist of two first-overtone Cepheids.
Type II Cepheids are recently becoming more important as distance indicators and astrophysics laboratory, although our knowledge of these stars is quite limited. Their evolutionary status is also not well understood and observational constraints are needed to confirm the current theories. We are presenting here our first results of the spectroscopic analysis of 4 of these systems. The masses of type II Cepheids seem consistent with the expected 0.5 − 0.6 M⊙. We also present first results of the fully modeled pulsator originally classified as peculiar W Vir star. The mass of this star is 1.51 ± 0.09 M⊙ and the p-factor 1.3 ± 0.03. It was eventually found not to belong to any typical Cepheid group
Mass and p-factor of the type II Cepheid OGLE-LMC-T2CEP-098 in a binary system
We present the results of a study of the type II Cepheid () in the eclipsing binary system OGLE-LMC-T2CEP-098 ().
The Cepheid belongs to the peculiar W Vir group, for which the evolutionary
status is virtually unknown. It is the first single-lined system with a
pulsating component analyzed using the method developed by Pilecki et al.
(2013). We show that the presence of a pulsator makes it possible to derive
accurate physical parameters of the stars even if radial velocities can be
measured for only one of the components. We have used four different methods to
limit and estimate the physical parameters, eventually obtaining precise
results by combining pulsation theory with the spectroscopic and photometric
solutions. The Cepheid radius, mass and temperature are ,
and , respectively, while its companion
has similar size (), but is more massive () and
hotter (). Our best estimate for the p-factor of the Cepheid is . The mass, position on the period-luminosity diagram, and pulsation
amplitude indicate that the pulsating component is very similar to the
Anomalous Cepheids, although it has a much longer period and is redder in
color. The very unusual combination of the components suggest that the system
has passed through a mass transfer phase in its evolution. More complicated
internal structure would then explain its peculiarity.Comment: 23 pages, 17 figures, accepted for publication in Ap
Cepheids with giant companions. I. Revealing a numerous population of double-lined binary Cepheids
Masses of classical Cepheids of 3 to 11 M are predicted by theory but
those measured, clump between 3.6 and 5 M. As a result, their
mass-luminosity relation is poorly constrained, impeding our understanding of
basic stellar physics and the Leavitt Law. All Cepheid masses come from the
analysis of 11 binary systems, including only 5 double-lined and well-suited
for accurate dynamical mass determination. We present a project to analyze a
new, numerous group of Cepheids in double-lined binary (SB2) systems to provide
mass determinations in a wide mass interval and study their evolution. We
analyze a sample of 41 candidate binary LMC Cepheids spread along the P-L
relation, that are likely accompanied by luminous red giants, and present
indirect and direct indicators of their binarity. In a spectroscopic study of a
subsample of 18 brightest candidates, for 16 we detected lines of two
components in the spectra, already quadrupling the number of Cepheids in SB2
systems. Observations of the whole sample may thus lead to quadrupling all the
Cepheid mass estimates available now. For the majority of our candidates,
erratic intrinsic period changes dominate over the light travel-time effect due
to binarity. However, the latter may explain the periodic phase modulation for
4 Cepheids. Our project paves the way for future accurate dynamical mass
determinations of Cepheids in the LMC, Milky Way, and other galaxies, which
will potentially increase the number of known Cepheid masses even 10-fold,
hugely improving our knowledge about these important stars.Comment: 12 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