ORCID Profile
0000-0001-5181-5072
Current Organisations
University of Antwerp
,
KU Leuven
,
Vrije Universiteit Brussel
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Publisher: AIP
Date: 2009
DOI: 10.1063/1.3246492
Publisher: Oxford University Press (OUP)
Date: 23-12-2016
Publisher: Oxford University Press (OUP)
Date: 26-11-2010
Publisher: AIP
Date: 2012
DOI: 10.1063/1.3701907
Publisher: American Astronomical Society
Date: 22-12-2021
Abstract: The Transiting Exoplanet Survey Satellite (TESS) space telescope is collecting continuous, high-precision optical photometry of stars throughout the sky, including thousands of RR Lyrae stars. In this paper, we present results for an initial s le of 118 nearby RR Lyrae stars observed in TESS Sectors 1 and 2. We use differential image photometry to generate light curves and analyze their mode content and modulation properties. We combine accurate light-curve parameters from TESS with parallax and color information from the Gaia mission to create a comprehensive classification scheme. We build a clean s le, preserving RR Lyrae stars with unusual light-curve shapes, while separating other types of pulsating stars. We find that a large fraction of RR Lyrae stars exhibit various low- litude modes, but the distribution of those modes is markedly different from those of the bulge stars. This suggests that differences in physical parameters have an observable effect on the excitation of extra modes, potentially offering a way to uncover the origins of these signals. However, mode identification is hindered by uncertainties when identifying the true pulsation frequencies of the extra modes. We compare mode litude ratios in classical double-mode stars to stars with extra modes at low litudes and find that they separate into two distinct groups. Finally, we find a high percentage of modulated stars among the fundamental mode pulsators, but also find that at least 28% of them do not exhibit modulation, confirming that a significant fraction of stars lack the Blazhko effect.
Publisher: EDP Sciences
Date: 09-2012
Publisher: EDP Sciences
Date: 11-2016
Publisher: Cambridge University Press (CUP)
Date: 07-2010
DOI: 10.1017/S1743921311010295
Abstract: The ultraviolet stellar wind lines of the photometrically periodic variable early B-type star σ Lupi were found to behave very similarly to what has been observed in known magnetic B stars, although no periodicity could be determined. AAT spectropolarimetric measurements with SEMPOL were obtained. We detected a longitudinal magnetic field with varying strength and litude of about 100 G with error bars of typically 20 G. This type of variability supports an oblique magnetic rotator model. We fold the equivalent width of the 4 usable UV spectra in phase with the well-known photometric period of 3.019 days, which we identify with the rotation period of the star. The magnetic field variations are consistent with this period. Additional observations with ESPaDOnS attached to the CFHT strongly confirmed this discovery, and allowed to determine a precise magnetic period. Like in the other magnetic B stars the wind emission likely originates in the magnetic equatorial plane, with maximum emission occurring when a magnetic pole points towards the Earth. The 3.0182 d magnetic rotation period is consistent with the photometric period, with maximum light corresponding to maximum magnetic field. No helium or other chemical peculiarity is known for this object.
Publisher: Oxford University Press (OUP)
Date: 22-09-2011
Publisher: Oxford University Press (OUP)
Date: 21-08-2007
Publisher: IOP Publishing
Date: 02-2010
DOI: 10.1086/650399
Publisher: EDP Sciences
Date: 10-2018
DOI: 10.1051/0004-6361/201833130
Abstract: Context . Based on their stellar parameters and the presence of a mid-IR excess due to circumstellar dust, RV Tauri stars have been classified as post-AGB stars. Our recent studies, however, reveal erse spectral energy distributions (SEDs) among RV Tauri stars, suggesting they may occupy other evolutionary channels as well. Aims . The aim of this paper is to present the erse SED characteristics of RV Tauri stars and investigate their evolutionary nature as a function of their SEDs. Methods . We carried out a systematic study of RV Tauri stars in the SMC and LMC because of their known distances and hence luminosities. Their SEDs were classified into three groups: dusty (disc-type), non-dusty (non-IR), and uncertain. A period-luminosity-colour (PLC) relation was calibrated. The luminosities from the PLC were complemented with those found using their SEDs and the stars were placed on a Hertzsprung-Russell diagram (HRD). I -band time series were used to search for period changes via ( O − C ) analyses to identify period changes. Results . The four main results from this study are: (1) RV Tauri stars with a clear IR excess have disc-type SEDs, which indicates that the dust is trapped in a stable disc. Given the strong link between disc-type SEDs and binarity in the Galaxy, we postulate that these are binaries as well. These cover a range of luminosities and we argue that the more luminous binaries are post-AGB stars while the lower luminosity binaries are likely post-red giant branch (post-RGB) stars. (2) Two of these objects have variable mean brightness with periods of 916 and 850 days, respectively, caused by variable extinction during orbital motion. (3) Non-dusty RV Tauri stars and objects with an uncertain SED evolve such that the circumstellar dust has dispersed. If they are single stars, they are post-AGB objects of low initial mass ( .25 M ⊙ ), while if they are binaries, the low-luminosity portion of the s le are likely post-RGB stars. (4) We find that RV Tauri stars with dust are on average more luminous than the rest of the s le.
No related grants have been discovered for Katrien Kolenberg.