J/A+A/601/A76 DIRECT lightcurves of 21 luminous YSGs in M33 (Kourniotis+, 2017)
Monitoring luminous yellow massive stars in M33:
new yellow hypergiant candidates.
Kourniotis M., Bonanos A.Z., Yuan W., Macri L.M., Garcia-Alvarez D.,
Lee C.-H.
<Astron. Astrophys. 601, A76 (2017)>
=2017A&A...601A..76K 2017A&A...601A..76K (SIMBAD/NED BibCode)
ADC_Keywords: Stars, supergiant ; Stars, variable ; Photometry, CCD
Keywords: galaxies: individual: M33 - stars: massive - stars: late-type -
stars: evolution - stars: variables: general
Abstract:
The evolution of massive stars surviving the red supergiant (RSG)
stage remains unexplored due to the rarity of such objects. The yellow
hypergiants (YHGs) appear to be the warm counterparts of post-RSG
classes located near the Humphreys-Davidson upper luminosity limit,
which are characterized by atmospheric instability and high mass-loss
rates.
We aim to increase the number of YHGs in M33 and thus to contribute to
a better understanding of the pre-supernova evolution of massive
stars.
Optical spectroscopy of five dust-enshrouded YSGs selected from mid-IR
criteria was obtained with the goal of detecting evidence of extensive
atmospheres. We also analyzed BVIc photometry for 21 of the most
luminous YSGs in M33 to identify changes in the spectral type. To
explore the properties of circumstellar dust, we performed SED-fitting
of multi-band photometry of the 21 YSGs. We find three luminous YSGs
in our sample to be YHG candidates, as they are surrounded by hot dust
and are enshrouded within extended, cold dusty envelopes. Our
spectroscopy of star 2 shows emission of more than one Hα
component, as well as emission of CaII, implying an extended
atmospheric structure. In addition, the long-term monitoring of the
star reveals a dimming in the visual light curve of amplitude larger
than 0.5mag that caused an apparent drop in the temperature that
exceeded 500K. We suggest the observed variability to be analogous to
that of the Galactic YHG ρ Cas. Five less luminous YSGs are
suggested as post-RSG candidates showing evidence of hot or/and cool
dust emission. We demonstrate that mid-IR photometry, combined with
optical spectroscopy and time-series photometry, provide a robust
method for identifying candidate YHGs. Future discovery of YHGs in
Local Group galaxies is critical for the study of the late evolution
of intermediate-mass massive stars.
Description:
File photom.dat contains the light curves of 21 luminous YSGs in M33
from Drout et al. (2012, Cat. J/ApJ/750/97). Observations were taken
in the BVIc as part of the DIRECT project (Macri et al., 2001, Cat.
J/AJ/121/861) and complemented with BVI observations taken between
2002 and 2006 from Pellerin & Macri (2011, Cat. J/ApJS/193/26). Only
stars with a V-band J variability index higher than 0.75 are included.
For each measurement we provide the LGGS designation, observing date,
band filter, magnitude and uncertainty.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
stars.dat 49 21 List of stars with photometry
photom.dat 44 5860 BVIc photometry of 21 luminous YSGs in M33
(table 1)
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See also:
J/AJ/121/861 : BVI photometry of central part of M33 (Macri+, 2001)
J/ApJS/193/26 : The M33 synoptic stellar survey. I. (Pellerin+, 2011)
J/ApJ/750/97 : The yellow and red supergiants of M33 (Drout+, 2012)
Byte-by-byte Description of file: stars.dat
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Bytes Format Units Label Explanations
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1- 4 A4 --- --- [LGGS]
6- 24 A19 --- LGGS LGGS designation of the star (JHHMMSS.ss+DDMMSS.s)
27- 28 I2 h RAh Simbad Right ascension (J2000.0)
30- 31 I2 min RAm Simbad Right ascension (J2000.0)
33- 37 F5.2 s RAs Simbad Right ascension (J2000.0)
39 A1 --- DE- Simbad Declination sign (J2000.0)
40- 41 I2 deg DEd Simbad Declination (J2000.0)
43- 44 I2 arcmin DEm Simbad Declination (J2000.0)
46- 49 F4.1 arcsec DEs Simbad Declination (J2000.0)
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Byte-by-byte Description of file: photom.dat
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Bytes Format Units Label Explanations
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1- 19 A19 --- LGGS LGGS designation of the star (JHHMMSS.ss+DDMMSS.s)
21 A1 --- Filter [BVI] Filter passband (Johnson-Cousins)
23- 31 F9.4 d JD Observation date (JD-2450000)
33- 38 F6.3 mag mag Magnitude in Filter
40- 44 F5.3 mag e_mag Uncertainty in magnitude
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Acknowledgements:
Michalis Kourniotis, mkourniotis(at)astro.noa.gr,
IAASARS, National Observatory of Athens, Greece
(End) Michalis Kourniotis [IAASAR, Greece], Patricia Vannier [CDS] 15-Feb-2017