On the new late B- and early A-type periodic variable stars

We summarize the properties of the new periodic, small-amplitude, variable stars recently discovered in the open cluster NGC 3766. They are located in the region of the Hertzsprung-Russell diagram between δ Sct and slowly pulsating B stars, a region where no sustained pulsation is predicted by standard models. The origin of their periodic variability is currently unknown. We also discuss how the Gaia mission, launched at the end of 2013, can contribute to our knowledge of those star

Ensemble Asteroseismology of the Young Open Cluster NGC 2244

Our goal is to perform in-depth ensemble asteroseismology of the young open cluster NGC2244 with the 2-wheel Kepler mission. While the nominal Kepler mission already implied a revolution in stellar physics for solar-type stars and red giants, it was not possible to perform asteroseismic studies of massive OB stars because such targets were carefully avoided in the FoV in order not to disturb the exoplanet hunting. Now is an excellent time to fill this hole in mission capacity and to focus on the metal factories of the Universe, for which stellar evolution theory is least adequate. Our white paper aims to remedy major shortcomings in the theory of stellar structure and evolution of the most massive stars by focusing on a large ensemble of stars in a carefully selected young open cluster. Cluster asteroseismology of very young stars such as those of NGC2244 has the major advantage that all cluster stars have similar age, distance and initial chemical composition, implying drastic restrictions for the stellar modeling compared to asteroseismology of single isolated stars with very different ages and metallicities. Our study requires long-term photometric measurements of stars with visual magnitude ranging from 6.5 to 15 in a large FoV with a precision better than 30 ppm for the brightest cluster members (magnitude below 9) up to 500 ppm for the fainter ones, which is well achievable with 2-Wheel Kepler, in combination with high-precision high-resolution spectroscopy and spectro-polarimetry of the brightest pulsating cluster members. These ground-based spectroscopic data will be assembled with the HERMES and CORALIE spectrographs (twin 1.2m Mercator and Euler telescopes, La Palma, Canary Islands and La Silla, Chile), as well as with the spectro-polarimetric NARVAL instrument (2m BLT at the Pic du Midi, French Pyrenees), to which we have guaranteed access.Comment: 10 pages, 3 figures, white paper submitted in response to the NASA call for community input for science investigations the Kepler 2-Wheel spacecraf

Extensive study of HD 25558, a long-period double-lined binary with two SPB components

We carried out an extensive observational study of the Slowly Pulsating B (SPB) star, HD 25558. The ≈2000 spectra obtained at different observatories, the ground-based and MOST satellite light curves revealed that this object is a double-lined spectroscopic binary with an orbital period of about nine years. The observations do not allow the inference of an orbital solution. We determined the physical parameters of the components, and found that both lie within the SPB instability strip. Accordingly, both show line-profile variations due to stellar pulsations. 11 independent frequencies were identified in the data. All the frequencies were attributed to one of the two components based on pixel-by-pixel variability analysis of the line profiles. Spectroscopic and photometric mode identification was also performed for the frequencies of both stars. These results suggest that the inclination and rotation of the two components are rather different. The primary is a slow rotator with ≈6 d period, seen at ≈60° inclination, while the secondary rotates fast with ≈1.2 d period, and is seen at ≈20° inclination. Spectropolarimetric measurements revealed that the secondary component has a magnetic field with at least a few hundred Gauss strength, while no magnetic field can be detected in the primary

TOI-199 b: A well-characterized 100-day transiting warm giant planet with TTVs seen from Antarctica

We present the spectroscopic confirmation and precise mass measurement of the warm giant planet TOI-199 b. This planet was first identified in TESS photometry and confirmed using ground-based photometry from ASTEP in Antarctica including a full 6.5$\,$h long transit, PEST, Hazelwood, and LCO; space photometry from NEOSSat; and radial velocities (RVs) from FEROS, HARPS, CORALIE, and CHIRON. Orbiting a late G-type star, TOI-199\,b has a $\mathrm{104.854_{-0.002}^{+0.001} \, d}$ period, a mass of $\mathrm{0.17\pm0.02 \, M_J}$, and a radius of $\mathrm{0.810\pm0.005 \, R_J}$. It is the first warm exo-Saturn with a precisely determined mass and radius. The TESS and ASTEP transits show strong transit timing variations, pointing to the existence of a second planet in the system. The joint analysis of the RVs and TTVs provides a unique solution for the non-transiting companion TOI-199 c, which has a period of $\mathrm{273.69_{-0.22}^{+0.26} \, d}$ and an estimated mass of $\mathrm{0.28_{-0.01}^{+0.02} \, M_J}$. This period places it within the conservative Habitable Zone.Comment: 33 pages, 23 figures. Accepted for publication in A

Towards asteroseismology of the young open stellar cluster Chi Persei (NGC 884).

Asteroseismologie is de studie van de inwendige sterstructuur door het i nterpreteren van de geobserveerde pulsatie-eigenschappen van een ster. J onge, massieve B-sterren zijn heel interessante objecten voor dit onderz oek, omdat ze de voorgangers zijn van supernovae en daardoor het Univers um chemisch zullen verrijken. Ons doel was een asteroseismologische stud ie uit te voeren van een open cluster, welke een natuurlijk laboratorium vormt voor studies over sterstructuur en -evolutie. Clustersterren word en immers gevormd uit dezelfde moleculaire wolk, wat inhoudt dat ze onge veer dezelfde afstand hebben vanaf de Aarde en gelijkaardige leeftijden en initiële chemische samenstellingen hebben. Dit leidt tot veel sterker e beperkingen bij de modellering van de pulserende clustersterren. Deze thesis bevat het observationele deel van één van de grootste a steroseismologische studies uitgevoerd op een open cluster, met als stud ieobject NGC 884, ook bekend als Chi Persei. We hebben een uitgebreide m ultisite campagne georganiseerd met als doel het verzamelen van voldoend e metingen voor de clustersterren. Veel aandacht ging uit naar de precie ze calibratie en reductie van de CCD-beelden tot interpreteerbare differ entiële lichtkrommes. Een nauwkeurigheid op millimagnitude-niveau werd b ereikt, wat een ideale start vormt voor het variabiliteits-onderzoek. Hi ervoor gebruikten we verschillende indicatoren, waarna een automatische frequentie-analyse uitgevoerd werd om de variabele sterren te classifici ëren. We ontdekten zo meer dan honderd nieuwe multi- en monoperiodieke B -, A- en F-type sterren. Hun interpretatie in termen van de klassieke in stabiliteitsdomeinen is niet zo vanzelfsprekend, wat op imperfecties in de theoretische instabiliteitsberekeningen wijst. Een gedetailleerde fre quentie-analyse en modus-identificatie waren toegespitst op de multiperi odieke B-sterren en we gaven een samenvatting van al hun observationele pulsatiekenmerken. Hiermee is aan de vereisten voor een asteroseismologi sche modellering van de B-sterren voldaan. Een gedetailleerde evaluatie van de sterevolutiemodellen is daarom veelbelovend. Zulke ensemble-aster oseismologie van de B-sterren in NGC 884 vormt een spin-off studie van d it observationele thesiswerk.status: publishe

Ensemble Asteroseismology of the Young Open Cluster NGC 2244

10 pages, 3 figures, white paper submitted in response to the NASA call for community input for science investigations the Kepler 2-Wheel spacecraftOur goal is to perform in-depth ensemble asteroseismology of the young open cluster NGC2244 with the 2-wheel Kepler mission. While the nominal Kepler mission already implied a revolution in stellar physics for solar-type stars and red giants, it was not possible to perform asteroseismic studies of massive OB stars because such targets were carefully avoided in the FoV in order not to disturb the exoplanet hunting. Now is an excellent time to fill this hole in mission capacity and to focus on the metal factories of the Universe, for which stellar evolution theory is least adequate. Our white paper aims to remedy major shortcomings in the theory of stellar structure and evolution of the most massive stars by focusing on a large ensemble of stars in a carefully selected young open cluster. Cluster asteroseismology of very young stars such as those of NGC2244 has the major advantage that all cluster stars have similar age, distance and initial chemical composition, implying drastic restrictions for the stellar modeling compared to asteroseismology of single isolated stars with very different ages and metallicities. Our study requires long-term photometric measurements of stars with visual magnitude ranging from 6.5 to 15 in a large FoV with a precision better than 30 ppm for the brightest cluster members (magnitude below 9) up to 500 ppm for the fainter ones, which is well achievable with 2-Wheel Kepler, in combination with high-precision high-resolution spectroscopy and spectro-polarimetry of the brightest pulsating cluster members. These ground-based spectroscopic data will be assembled with the HERMES and CORALIE spectrographs (twin 1.2m Mercator and Euler telescopes, La Palma, Canary Islands and La Silla, Chile), as well as with the spectro-polarimetric NARVAL instrument (2m BLT at the Pic du Midi, French Pyrenees), to which we have guaranteed access

The ongoing 2005 -- 2006 campaign on beta Cephei stars in NGC 6910 and chi Persei (NGC 884)

International audienc