G. C. Van de Steene

Royal Observatory of Belgium

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P. A. M. van Hoof

Royal Observatory of Belgium

H. Van Winckel

KU Leuven

A. A. Zijlstra

University of Manchester

Toshiya Ueta

University of Denver

M. J. Barlow

University College London

M. A. T. Groenewegen

Royal Observatory of Belgium

M. Matsuura

Cardiff University

P. Royer

KU Leuven

S. Kimeswenger

Universität Innsbruck

R. Wesson

University College London

Cooperative Institutions

KU Leuven

100

Institute of Astronomy

Centre National de la Recherche Scientifique

Max Planck Society

Consejo Nacional de Investigaciones Científicas y Técnicas

Royal Observatory of Belgium

Australian National University

Commonwealth Scientific and Industrial Research Organisation

University of Sydney

Astronomy and Space

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The very fast evolution of Sakurai's object

Proceedings of the International Astronomical Union (2016)

G. C. Van de Steene P. A. M. van Hoof S. Kimeswenger A. A. Zijlstra A. Avison

V4334 Sgr (a.k.a. Sakurai's object) is the central star of an old planetary nebula that underwent a very late thermal pulse a few years before its discovery in 1996. We have been monitoring the evolution of the optical emission line spectrum since 2001. The goal is to improve the evolutionary models by constraining them with the temporal evolution of the central star temperature. In addition the high resolution spectral observations obtained by X-shooter and ALMA show the temporal evolution of the different morphological components.

Star (game theory)

Temporal resolution

Time evolution

10.1017/s1743921317000588

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Citations (4)

The PNLF distance to the Sculptor Group galaxy NGC 55

arXiv (Cornell University) (2004)

G. C. Van de Steene G. H. Jacoby C. Praet R. Ciardullo H. Dejonghe

We identified 21 new Planetary Nebula (PN) candidates in the Sculptor Group galaxy NGC 55. We determined a most likely distance of 2.00 +/- 0.2 Mpc using the Planetary Nebulae Luminosity Function (PNLF) method. The distance to NGC 55 is larger than previously determined distances, which means that the Sculptor Group is a bit further away from the Local Group than previously thought. The distance to NGC 55 is again similar to the distance of NGC 300, adding support to the suggestion that these galaxies form a bound pair.

Hubble sequence

Local Group

10.48550/arxiv.astro-ph/0407348

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IRAS 12316--6401: a New Symbiotic Mira?

Open Astronomy (2007)

P. A. M. van Hoof G. C. Van de Steene

Symbiotic star

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Spectroscopy of New Planetary Nebulae Close to the Galactic Center

Planetary Nebulae (1997)

G. C. Van de Steene George H. Jacoby

Planetary Nebulae (PN) are bright emission line objects, observable at large distances throughout the Galaxy. They serve as probes of abundance gradients and chemical enrichment history of the ISM.

Center (category theory)

10.1007/978-94-011-5244-0_202

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Multi-technique investigation of the binary fraction of A-F type candidate hybrid variable stars discovered byKepler

Astronomy and Astrophysics (2017)

P. Lampens Y. Frémat L. Vermeylen Á. Sódor M. Skarka

Context. Hundreds of candidate hybrid pulsators of intermediate type A–F were revealed by recent space missions. Hybrid pulsators allow us to study the full stellar interiors, where both low-order p - and high-order g -modes are simultaneously excited. The true hybrid stars must be identified since other processes, related to stellar multiplicity or rotation, might explain the presence of (some) low frequencies observed in their periodograms. Aims. We measured the radial velocities of 50 candidate δ Scuti − γ Doradus hybrid stars from the Kepler mission with the Hermes and ace spectrographs over a time span of months to years. We aim to derive the fraction of binary and multiple systems and to provide an independent and homogeneous determination of the atmospheric properties and v sin i for all targets. The long(er)-term objective is to identify the (probable) physical cause of the low frequencies. Methods. We computed one-dimensional cross-correlation functions (CCFs) in order to find the best set of parameters in terms of the number of components, spectral type(s), and v sin i for each target. Radial velocities were measured using spectrum synthesis and a two-dimensional cross-correlation technique in the case of double- and triple-lined systems. Fundamental parameters were determined by fitting (composite) synthetic spectra to the normalised median spectra corrected for the appropriate Doppler shifts. Results. We report on the analysis of 478 high-resolution Hermes and 41 ace spectra of A/F-type candidate hybrid pulsators from the Kepler field. We determined their radial velocities, projected rotational velocities, and atmospheric properties and classified our targets based on the shape of the CCFs and the temporal behaviour of the radial velocities. We derived orbital solutions for seven new systems. Three preliminary long-period orbital solutions are confirmed by a photometric time-delay analysis. Finally, we determined a global multiplicity fraction of 27% in our sample of candidate hybrid stars.

Radial velocity

Effective temperature

10.1051/0004-6361/201730694

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Citations (26)

Recombination of Hot Ionized Nebulae: The Old Planetary Nebula around V4334 Sgr (Sakurai’s Star)*

The Astrophysical Journal (2022)

Martin Reichel S. Kimeswenger P. A. M. van Hoof A. A. Zijlstra Daniela Barría

After becoming ionized, low-density astrophysical plasmas will begin a process of slow recombination. Models for this still have significant uncertainties. The recombination cannot normally be observed in isolation, because the ionization follows the evolutionary time scale of the ionizing source. Laboratory experiments are unable to reach the appropriate conditions because of the required very long time scales. The extended nebula around the very late helium flash (VLTP) star V4334 Sgr provides a unique laboratory for this kind of study. The sudden loss of the ionizing UV radiation after the VLTP event has allowed the nebula to recombine free from other influences. More than 290 long slit spectra taken with FORS1/2 at the ESO VLT between 2007 and 2022 are used to follow the time evolution of lines of H, He, N, S, O, Ar. Hydrogen and helium lines, representing most of the ionized mass, do not show significant changes. A small increase is seen in [N II] (+2.8 %/yr; significance 2.7 sigma), while we see a decrease in [O III] (-1.96 %/yr; 2.0 sigma). The [S II] lines show a change of +3.0 %/yr; 1.6 sigma). The lines of [S III] and of Ar III] show no significant change. For [S III], the measurement differs from the predicted decrease by 4.5 sigma. A possible explanation is that the fraction of [S IV] and higher is larger than expected. Such an effect could provide a potential solution for the sulfur anomaly in planetary nebulae.

Star (game theory)

Dark nebula

10.3847/1538-4357/ac90c4

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Results from the Herschel Key Program MESS

M. A. T. Groenewegen C. Waelkens M. J. Barlow F. Kerschbaum P. García-Lario

MESS (Mass loss of Evolved StarS) is a Herschel Guaranteed Time Key Program that will image about 100, and do spectroscopy of about 50, post-main-sequence objects of all flavours: AGB stars, post-AGB stars, planetary nebulae, luminous blue variables, Wolf-Rayet stars, and supernova remnants. In this review the implementation and current status of MESS is outlined, and first results are presented.

Wolf–Rayet star

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Non-thermal radio emission in Sakurai's Object

Astronomy and Astrophysics (2024)

M. Hajduk P. A. M. van Hoof A. A. Zijlstra G. C. Van de Steene S. Kimeswenger

The very late thermal pulse (VLTP) affects the evolution of $\sim$20\% of 1--8\,$\mathrm M_\odot$ stars, repeating the last phases of the red giant within a few years and leading to the formation of a new, but hydrogen-poor nebula within the old planetary nebula (PN). The strong dust formation in the latter obscures the optical and near-infrared radiation of the star. We aimed to determine the reheating timescale of the central star in Sakurai's object, which is an important constraint for the poorly understood VLTP evolution. We observed the radio continuum emission of Sakurai's object for almost 20 years from 2004 to 2023. Continuous, multi-frequency observations proved to be essential to distinguish between phases dominated by photoionization and shock ionization. The flux density fluctuates by more than a factor 40 within months to years. The spectral index remained negative between 2006 and 2017 and is close to zero since 2019. The emission region is barely resolved since 2021. Non-thermal radio emission observed from 2004 to 2017 traces shocks induced by wind interactions due to discrete mass-loss events. Thermal emission dominates during the period 2019--2023 and may indicate photoionization of the nebula by the central star.

H II region

Spectral index

10.1051/0004-6361/202450496

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Citations (3)

Comet 55P/1997 E1 (Tempel-Tuttle)

IAUC (1997)

O. Hainaut K. J. Meech J. Bauer P. Martín K. Mueller

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Gravity-mode period spacings as seismic diagnostic for a sample of gamma Doradus stars from Kepler space photometry and high-resolution ground-based spectroscopy

arXiv (Cornell University) (2015)

T. Van Reeth A. Tkachenko C. Aerts P. I. Papics S. A. Triana

Gamma Doradus stars (hereafter gamma Dor stars) are gravity-mode pulsators of spectral type A or F. Such modes probe the deep stellar interior, offering a detailed fingerprint of their structure. Four-year high-precision space-based Kepler photometry of gamma Dor stars has become available, allowing us to study these stars with unprecedented detail. We selected, analysed, and characterized a sample of 67 gamma Dor stars for which we have Kepler observations available. For all the targets in the sample we assembled high-resolution spectroscopy to confirm their F-type nature. We found fourteen binaries, among which four single-lined binaries, five double-lined binaries, two triple systems and three binaries with no detected radial velocity variations. We estimated the orbital parameters whenever possible. For the single stars and the single-lined binaries, fundamental parameter values were determined from spectroscopy. We searched for period spacing patterns in the photometric data and identified this diagnostic for 50 of the stars in the sample, 46 of which are single stars or single-lined binaries. We found a strong correlation between the spectroscopic vsini and the period spacing values, confirming the influence of rotation on gamma Dor-type pulsations as predicted by theory. We also found relations between the dominant g-mode frequency, the longest pulsation period detected in series of prograde modes, vsini, and log Teff.

Rotation period

10.48550/arxiv.1504.02119

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Citations (2)