TY - JOUR A1 - Fulmer, Leah M. A1 - Gallagher, John S. A1 - Hamann, Wolf-Rainer A1 - Oskinova, Lida A1 - Ramachandran, Varsha T1 - Testing massive star evolution, star-formation history, and feedback at low metallicity BT - photometric analysis of OB stars in the SMC Wing JF - Astronomy and astrophysics : an international weekly journal N2 - Context. The supergiant ionized shell SMC-SGS 1 (DEM 167), which is located in the outer Wing of the Small Magellanic Cloud (SMC), resembles structures that originate from an energetic star-formation event and later stimulate star formation as they expand into the ambient medium. However, stellar populations within and surrounding SMC-SGS 1 tell a different story. Aims. We present a photometric study of the stellar population encompassed by SMC-SGS 1 in order to trace the history of such a large structure and its potential influence on star formation within the low-density, low-metallicity environment of the SMC. Methods. For a stellar population that is physically associated with SMC-SGS 1, we combined near-ultraviolet (NUV) photometry from the Galaxy Evolution Explorer with archival optical (V-band) photometry from the ESO Danish 1.54 m Telescope. Given their colors and luminosities, we estimated stellar ages and masses by matching observed photometry to theoretical stellar isochrone models. Results. We find that the investigated region supports an active, extended star-formation event spanning similar to 25-40 Myr ago, as well as continued star formation into the present. Using a standard initial mass function, we infer a lower bound on the stellar mass from this period of similar to 3 x 10(4) M-circle dot, corresponding to a star-formation intensity of similar to 6 x 10(-3) M-circle dot kpc(-2) yr(-1). Conclusions. The spatial and temporal distributions of young stars encompassed by SMC-SGS 1 imply a slow, consistent progression of star formation over millions of years. Ongoing star formation, both along the edge and interior to SMC-SGS 1, suggests a combined stimulated and stochastic mode of star formation within the SMC Wing. We note that a slow expansion of the shell within this low-density environment may preserve molecular clouds within the volume of the shell, leaving them to form stars even after nearby stellar feedback expels local gas and dust. KW - galaxies KW - stellar content KW - stars KW - formation KW - individual KW - Small KW - Magellanic Cloud Y1 - 2020 U6 - https://doi.org/10.1051/0004-6361/201834314 SN - 0004-6361 SN - 1432-0746 VL - 633 PB - EDP Sciences CY - Les Ulis ER - TY - JOUR A1 - Charpinet, Stéphane A1 - Brassard, P. A1 - Fontaine, G. A1 - Van Grootel, Valerie A1 - Zong, Weika A1 - Giammichele, N. A1 - Heber, Ulrich A1 - Bognár, Zsófia A1 - Geier, Stephan Alfred A1 - Green, Elizabeth M. A1 - Hermes, J. J. A1 - Kilkenny, D. A1 - Ostensen, R. H. A1 - Pelisoli, Ingrid Domingos A1 - Silvotti, R. A1 - Telting, J. H. A1 - Vuckovic, Maja A1 - Worters, H. L. A1 - Baran, Andrzej S. A1 - Bell, Keaton J. A1 - Bradley, Paul A. A1 - Debes, J. H. A1 - Kawaler, S. D. A1 - Kolaczek-Szymanski, P. A1 - Murphy, S. J. A1 - Pigulski, A. A1 - Sodor, A. A1 - Uzundag, Murat A1 - Handberg, R. A1 - Kjeldsen, H. A1 - Ricker, G. R. A1 - Vanderspek, R. K. T1 - TESS first look at evolved compact pulsators Discovery and asteroseismic probing of the g-mode hot B subdwarf pulsator EC 21494-7018 JF - Astronomy and astrophysics : an international weekly journal N2 - Context. The TESS satellite was launched in 2018 to perform high-precision photometry from space over almost the whole sky in a search for exoplanets orbiting bright stars. This instrument has opened new opportunities to study variable hot subdwarfs, white dwarfs, and related compact objects. Targets of interest include white dwarf and hot subdwarf pulsators, both carrying high potential for asteroseismology. Aims. We present the discovery and detailed asteroseismic analysis of a new g-mode hot B subdwarf (sdB) pulsator, EC 21494-7018 (TIC 278659026), monitored in TESS first sector using 120-s cadence. Methods. The TESS light curve was analyzed with standard prewhitening techniques, followed by forward modeling using our latest generation of sdB models developed for asteroseismic investigations. By simultaneously best-matching all the observed frequencies with those computed from models, we identified the pulsation modes detected and, more importantly, we determined the global parameters and structural configuration of the star. Results. The light curve analysis reveals that EC 21494-7018 is a sdB pulsator counting up to 20 frequencies associated with independent g-modes. The seismic analysis singles out an optimal model solution in full agreement with independent measurements provided by spectroscopy (atmospheric parameters derived from model atmospheres) and astrometry (distance evaluated from Gaia DR2 trigonometric parallax). Several key parameters of the star are derived. Its mass (0.391 +/- 0.009x2006;M-circle dot) is significantly lower than the typical mass of sdB stars and suggests that its progenitor has not undergone the He-core flash; therefore this progenitor could originate from a massive (greater than or similar to 2;M-circle dot) red giant, which is an alternative channel for the formation of sdBs. Other derived parameters include the H-rich envelope mass (0.0037 +/- 0.0010;M-circle dot), radius (0.1694 +/- 0.0081;R-circle dot), and luminosity (8.2 +/- 1.1;L-circle dot). The optimal model fit has a double-layered He+H composition profile, which we interpret as an incomplete but ongoing process of gravitational settling of helium at the bottom of a thick H-rich envelope. Moreover, the derived properties of the core indicate that EC 21494-7018 has burnt similar to 43% (in mass) of its central helium and possesses a relatively large mixed core (M-core;=;0.198 +/- 0.010;M-circle dot), in line with trends already uncovered from other g-mode sdB pulsators analyzed with asteroseismology. Finally, we obtain for the first time an estimate of the amount of oxygen (in mass; X(O)(core) = 0.16(-0.05)(+0.13)X(O)core=0.16-0.05+0.13$ X(mathrm{O})_{mathrm{core}}=0.16_{-0.05}<^>{+0.13} $) produced at this stage of evolution by an helium-burning core. This result, along with the core-size estimate, is an interesting constraint that may help to narrow down the still uncertain C-12(alpha,;gamma)O-16 nuclear reaction rate. KW - asteroseismology KW - stars KW - interiors KW - oscillations KW - horizontal-branch KW - individual KW - TIC 278659026 KW - subdwarfs Y1 - 2019 U6 - https://doi.org/10.1051/0004-6361/201935395 SN - 0004-6361 SN - 1432-0746 VL - 632 PB - EDP Sciences CY - Les Ulis ER - TY - JOUR A1 - Alexoudi, Xanthippi T1 - On the parameter refinement of inflated exoplanets with large radius uncertainty based on TESS observations JF - Astronomische Nachrichten = Astronomical notes N2 - We revisited 10 known exoplanetary systems using publicly available data provided by the transiting exoplanet survey satellite (TESS). The sample presented in this work consists of short period transiting exoplanets, with inflated radii and large reported uncertainty on their planetary radii. The precise determination of these values is crucial in order to develop accurate evolutionary models and understand the inflation mechanisms of these systems. Aiming to evaluate the planetary radius measurement, we made use of the planet-to-star radii ratio, a quantity that can be measured during a transit event. We fit the obtained transit light curves of each target with a detrending model and a transit model. Furthermore, we used emcee, which is based on a Markov chain Monte Carlo approach, to assess the best fit posterior distributions of each system parameter of interest. We refined the planetary radius of WASP-140 b by approximately 12%, and we derived a better precision on its reported asymmetric radius uncertainty by approximately 86 and 67%. We also refined the orbital parameters of WASP-120 b by 2 sigma. Moreover, using the high-cadence TESS datasets, we were able to solve a discrepancy in the literature, regarding the planetary radius of the exoplanet WASP-93 b. For all the other exoplanets in our sample, even though there is a tentative trend that planetary radii of (near-) grazing systems have been slightly overestimated in the literature, the planetary radius estimation and the orbital parameters were confirmed with independent observations from space, showing that TESS and ground-based observations are overall in good agreement. KW - planetary systems KW - techniques KW - photometric KW - stars KW - WASP-140 KW - HAT-P-16 KW - WASP-108 KW - WASP-113 KW - WASP-120 KW - WASP-123 KW - WASP-136 KW - WASP-20 KW - WASP-76 KW - WASP-93 Y1 - 2022 U6 - https://doi.org/10.1002/asna.20224012 SN - 0004-6337 SN - 1521-3994 VL - 343 IS - 3 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Ilin, Ekaterina A1 - Poppenhäger, Katja A1 - Alvarado-Gómez, Julián David T1 - Localizing flares to understand stellar magnetic fields and space weather in exo-systems JF - Astronomische Nachrichten = Astronomical notes N2 - Stars are uniform spheres, but only to first order. The way in which stellar rotation and magnetism break this symmetry places important observational constraints on stellar magnetic fields, and factors in the assessment of the impact of stellar activity on exoplanet atmospheres. The spatial distribution of flares on the solar surface is well known to be nonuniform, but elusive on other stars. We briefly review the techniques available to recover the loci of stellar flares, and highlight a new method that enables systematic flare localization directly from optical light curves. We provide an estimate of the number of flares we may be able to localize with the Transiting Exoplanet Survey Satellite, and show that it is consistent with the results obtained from the first full sky scan of the mission. We suggest that nonuniform flare latitude distributions need to be taken into account in accurate assessments of exoplanet habitability. KW - stars KW - activity - stars KW - flare - stars KW - magnetic fields - methods KW - data KW - analysis Y1 - 2022 U6 - https://doi.org/10.1002/asna.20210111 SN - 1521-3994 VL - 343 IS - 4 PB - Berlin CY - Wiley-VCH ER - TY - JOUR A1 - Foster, Grace A1 - Poppenhäger, Katja T1 - Identifying interesting planetary systems for future X-ray observations JF - Astronomische Nachrichten = Astronomical notes N2 - X-ray observations of star-planet systems are important to grow our understanding of exoplanets; these observations allow for studies of photoevaporation of the exoplanetary atmosphere, and in some cases even estimations of the size of the outer planetary atmosphere. The German-Russian eROSITA instrument onboard the SRG (Spectrum Roentgen Gamma) mission is performing the first all-sky X-ray survey since the 1990s, and provides X-ray fluxes and spectra of exoplanet host stars over a much larger volume than was accessible before. Using new eROSITA data as well as archival data from XMM-Newton, Chandra, and ROSAT, we estimate mass-loss rates of exoplanets under an energy-limited escape scenario and identify several exoplanets with strong X-ray irradiation and expected mass loss that are amenable to follow-up observations at other wavelengths. We model sample spectra using a toy model of an exoplanetary atmosphere to predict what exoplanet transit observations with future X-ray missions such as Athena will look like and estimate the observable X-ray transmission spectrum for a typical hot Jupiter-type exoplanet. KW - planets and satellites KW - general KW - stars KW - activity KW - coronae KW - planetary systems KW - X-rays Y1 - 2022 U6 - https://doi.org/10.1002/asna.20220007 SN - 1521-3994 VL - 343 IS - 4 PB - Wiley-VCH CY - Berlin ER - TY - JOUR A1 - Poppenhäger, Katja T1 - How stars and planets interact BT - A look through the high-energy window JF - Astronomische Nachrichten = Astronomical notes N2 - The architecture of exoplanetary systems is often different from the solar system, with some exoplanets being in close orbits around their host stars and having orbital periods of only a few days. In analogy to interactions between stars in close binary systems, one may expect interactions between the star and the exoplanet as well. From theoretical considerations, effects on the host star through tidal and magnetic interaction with the exoplanet are possible; for the exoplanet, some interesting implications are the evaporation of the planetary atmosphere and potential effects on the planetary magnetism. In this review, several possible interaction pathways and their observational prospects and existing evidence are discussed. A particular emphasis is put on observational opportunities for these kinds of effects in the high-energy regime. KW - magnetic fields KW - planet-star interactions KW - stars KW - activity KW - X-rays Y1 - 2019 U6 - https://doi.org/10.1002/asna.201913619 SN - 0004-6337 SN - 1521-3994 VL - 340 IS - 4 SP - 329 EP - 333 PB - Wiley-VCH CY - Weinheim ER -