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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 (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:
FileName Lrecl Records Explanations
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)
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
Bytes Format Units Label Explanations
1- 4 A4 --- --- [LGGS] 6- 24 A19 --- LGGS LGGS designation of the star ( 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)
Byte-by-byte Description of file: photom.dat
Bytes Format Units Label Explanations
1- 19 A19 --- LGGS LGGS designation of the star ( 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
Acknowledgements: Michalis Kourniotis, mkourniotis(at), IAASARS, National Observatory of Athens, Greece
(End) Michalis Kourniotis [IAASAR, Greece], Patricia Vannier [CDS] 15-Feb-2017
The document above follows the rules of the Standard Description for Astronomical Catalogues.From this documentation it is possible to generate f77 program to load files into arrays or line by line

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