J/A+A/603/A70 Type II and anomalous Cepheids luminosities (Groenewegen+, 2017)
Luminosities and infrared excess in Type II and anomalous Cepheids in the
Large and Small Magellanic Clouds.
Groenewegen M., Jurkovic M.I.
<Astron. Astrophys. 603, A70 (2017)>
=2017A&A...603A..70G 2017A&A...603A..70G (SIMBAD/NED BibCode)
ADC_Keywords: Magellanic Clouds ; Stars, variable
Keywords: stars: variables: Cepheids - stars: fundamental parameters -
Magellanic Clouds
Abstract:
Type II and anomalous Cepheids (ACs) are useful distance indicators
when there are too few classical Cepheids or when RR Lyrae stars are
too faint. Type II and ACs follow a period-luminosity relation as
well, but they are less well-studied classes of objects. In this paper
we study the sample of 335 Type II and ACs in the Small and Large
Magellanic Clouds detected in OGLE-III data. The spectral energy
distributions (SEDs) are constructed from photometric data available
in the literature and fitted with a dust radiative transfer model,
thereby leading to a determination of luminosity and effective
temperature. In addition, a subsample of targets is investigated for
possible binarity by looking for the light-time travel effect (LITE).
Hertzsprung-Russell diagrams (HRD) are constructed and compared to
evolutionary tracks and theoretical instability strips (ISs). In
agreement with previous suggestions, the BL Her subclass can be
explained by the evolution of ∼0.5-0.6M☉ stars evolving off
the zero-age horizontal branch and the ACs can be explained by the
evolution of ∼1.1-2.3M☉ stars. The evolution of the W Vir
subclass is not clear. These objects are at higher luminosities than
ACs and evolutionary tracks of ∼2.5-4M☉ stars cross this
region in the HRD, but the periods of the W Vir are longer than those
of the short period classical Cepheids at these luminosities, which
indicates the former have lower masses. A low-mass star experiencing a
thermal pulse when the envelope mass is small can make a blue loop
into the IS region of the W Vir stars. But the timescale is extremely
short, so this is also no explanation for the W Vir as a class. A
relation to binarity might be at the origin of the W Vir stars, which
has already been explicitly suggested for the peculiar W Vir stars.
For ∼60% of the RV Tau and ∼10% of the W Vir objects an infrared
excess is detected from the SED fitting. A recent result is confirmed
that stars exist with luminosities below that predicted from
single-star evolution, which show a clear infrared excess, and the
shape of the excess suggests a connection to binary evolution. The
investigation of the LITE effect revealed 20 systems that appear to
show periodic variations and may be new binaries, although this study
requires follow-up. About 40 stars show significant period changes.
Description:
We used the OGLE-III sample of T2Cs and ACs introduced by Soszynski et
al. (2008, Cat. J/AcA/58/293, updated in 2009 in the online catalogue
(ftp://ftp.astrouw.edu.pl/ogle/ogle3/OIII-CVS) and Soszynski et al.
(2010, Cat. J/AcA/61/285).
The SEDs were constructed using photometry retrieved mostly, but not
exclusively, via the VizieR web interface
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablea1.dat 141 333 Parameters resulting from the fitting of the
spectral energy distributions
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See also:
J/AcA/58/293 : Type-II and anomalous Cepheids in LMC (Soszynski+, 2008)
J/AcA/60/91 : VI light curves of SMC type II Cepheids (Soszynski+, 2010)
J/AcA/65/233 : OGLE Magellanic Clouds anomalous Cepheids (Soszynski+, 2015)
Byte-by-byte Description of file: tablea1.dat
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Bytes Format Units Label Explanations
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1- 18 A18 --- Name OGLE-III Identifier (1)
20- 24 A5 --- Type Type of variability (ANCEP or T2CEP)
26- 30 A5 --- Sub-type Sub-type of variability (2)
32- 38 F7.3 d Period Pulsation period
40- 43 I4 Lsun Lum Luminosity
45- 48 I4 Lsun e_Lum Error in the luminosity
50- 53 I4 K Teff Effective temperature
55- 58 I4 K e_Teff Error in the effective temperature
60- 64 F5.3 --- tau Dust optical depth at 0.55 micron
66- 69 I4 K Tc Dust temperature at the inner radius
71 I1 --- fit [0/1] Is Tc fitted (1), or not (0)
73-141 A69 --- Remarks Remarks
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Note (1): OGLE-LMC-ACEP-NNN, OGLE-LMC-T2CEP-NNN (Cat. J/AcA/65/233),
OGLE-SMC-ACEP-NNN (Cat. J/AcA/58/293), OGLE-SMC-T2CEP-NNN (Cat. J/AcA/60/91),
OGLE SMC-* or OGLE LMC-* in Simbad.
Note (2): F or 1O for ANCEP; RVTau, BLHer, WVir, pWVir for T2CEP.
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Acknowledgements:
Martin Groenewegen, martin.groenewegen(at)oma.be
(End) Patricia Vannier [CDS] 26-Apr-2017