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J/A+A/597/A55       Corot photometry of TYC 455-791-1       (Strassmeier+, 2017)

CoRoT photometry and STELLA spectroscopy of an eccentric, eclipsing and spotted HgMn binary with sub-synchronized rotation. Strassmeier K.G., Granzer T., Mallonn M., Weber M., Weingrill J. <Astron. Astrophys. 597, A55 (2017)> =2017A&A...597A..55S (SIMBAD/NED BibCode)
ADC_Keywords: Binaries, eclipsing ; Photometry, special systems ; Stars, peculiar Keywords: stars: eclipsing - stars: peculiar - stars: rotation - stars: binaries - stars: starspots - stars: HSS 348 - stars: early-type - stars: TYC 455-791-1 - open clusters: IC 4756 Abstract: We report the discovery and analysis of very narrow transits in the eccentric spectroscopic binary TYC 455-791-1=HSS 348 (IC 4756). We obtained high-precision CoRoT photometry over two long runs and multi-epoch high-resolution echelle spectroscopy and imaging with STELLA. Standard radial-velocity extraction, spectrum synthesis, Fourier analysis, and light-curve inversions are applied to the data. HSS 348 is found to be an eccentric (e=0.18) double-lined spectroscopic binary with a period of 12.47 d in which at least the primary component is a peculiar B star of the HgMn class. The orbital elements are such that the system undergoes a grazing eclipse with the primary in front but no secondary eclipse. The out-of-eclipse light variations show four nearly equidistant but unequal minima stable in shape and amplitude throughout our observations. Their individual photometric periods are all harmonics of the same fundamental period which happens to agree with the transit period to within the errors. We interpret the fundamental period to be the rotation period of at least one if not both stars due to surface inhomogeneities. Due to the non-zero eccentricity of the orbit the two components are rotating sub-synchronously. It appears that HSS 348 is not a member of the IC 4756 cluster but a background B8+B8.5 binary system. Its sharp eclipses every 12.47 days just mimic a small-body transit but are in reality the grazing eclipses of a B-star binary and thus a classical false positive. The system seems to be pre-main sequence with the primary possibly just arrived on the ZAMS. The light curve with four unequal minima can be explained with four cool spots of different size equidistantly positioned in longitude. Our data do not allow to uniquely assign the spots to either of the two stars. Description: From the original CoRoT white-light flux obtained on two consecutive runs, we filter out obvious outliers from the SAA (south Atlantic Anomaly). The third column are the remaining CoRoT data points. The two data set were merged using individual zero-points of 716386.54e- for the first data set and 721882.56e- for the second data set, respectively. The magnitudes thus calculates are in column four. The last column is the combined model of the transit plus a 12th order Fourier-series fit to the out-of-transit data. Objects: --------------------------------------------------------------------- RA (2000) DE Designation(s) --------------------------------------------------------------------- 18 39 44.3 +05 01 23 HSS 348 = TYC 455-791-1 = Cl* IC 4756 HER 348 --------------------------------------------------------------------- File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file hss348.dat 42 405929 Time series photometry CoRot flux, normalized magnitudes and model (tableA1)
See also: B/corot : CoRoT observation log (N2-4.4) (CoRoT 2016) Byte-by-byte Description of file: hss348.dat
Bytes Format Units Label Explanations
2- 13 F12.7 d HJD Heliocentric Julian date (HJD-2451545) 15- 22 F8.6 --- Phase Orbital phase 24- 32 F9.6 mag magObs Zero-point corrected magnitude from white flux 34- 42 F9.6 mag magMod Modelled magnitude
Acknowledgements: Thomas Granzer, tgranzer(at)
(End) Thomas Granzer [AIP, Germany], Patricia Vannier [CDS] 16-Nov-2016
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