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- ItemResolving stellar populations with integral field spectroscopy(Berlin : Wiley-VCH Verl., 2019) Roth, Martin M.; Weilbacher, Peter M.; Castro, NorbertoHigh-performance instruments at large ground-based telescopes have made integral field spectroscopy (IFS) a powerful tool for the study of extended objects such as galaxies, nebulae, or even larger survey fields on the sky. Here, we discuss the capabilities of IFS for the study of resolved stellar populations, using the newmethod of point-spread-function-fitting crowded field IFS, analogous to the well-established technique of crowded field photometry with image sensors.We review early pioneering work with first-generation integral field spectrographs, the breakthrough achieved with the multiunit spectral explorer (MUSE) instrument at the European Organisation for Astronomical Research in the Southern Hemisphere (ESO)Very Large Telescope, the remarkable progress accomplished with MUSE in the study of globular clusters, and first results on nearby galaxies. We discuss the synergy of integral field spectrographs at 8–10 mclass telescopes with future facilities such as the extremely large telescope (ELT).
- ItemComparison of telescopic and naked-eye sunspots for the very small spots on February 15, 1900 and January 30, 1911(Berlin : Wiley-VCH Verl., 2020) Neuhäuser, Ralph; Geymeier, Michael; Arlt, Rainer; Chapman, JesseIn a recent discussion of the Maunder Minimum, two sunspot observations by Chinese court astronomers on February 15, 1900 and January 30, 1911 (±1 day) – presumably made with the unaided eye – were considered false detections because the spot areas of the largest spot on those days (±1 day) as recorded by the Royal Greenwich Observatory, would be too small for naked-eye detection, namely 11 and 13 millionths of a solar disk (msd), respectively (Usoskin et al. 2015). We revisit this issue here. First, we review theoretical and empirical considerations of the lower limit for the sunspot area detectable by the naked eye: under optimal conditions, very good observers can detect spots as small as ∼100 msd (and we present one example, where an observer reported a spot, when the largest spot on that day was only 65 msd, but being part of a longish group facilitating the detection). Then, we review all known sunspot observations on and around February 15, 1900 and January 30, 1911, including full-disk drawings. For February 15, 1900, Kalocsa observatory, Hungary, shows a feature close to the western limb with an area of 134 msd, but it is not clear whether it was a spot or faculae or pores (as spot, it could have been detectable even by naked-eye). The two spot groups detected in Kodaikanal, India, on January 31, 1911 and February 1 with 18.5 to 33.0 msd area would be too small for detection by the naked eye. However, the Chinese records for February 15, 1900 and January 30, 1911 do not even mention whether the observations were performed with a telescope or by the unaided eye. We conclude that there is no convincing evidence that these two – or even all – Chinese sunspot records are unreliable.
- ItemPTF1J2224+17: A short-period, high-field polar(Berlin : Wiley-VCH Verl., 2020) Schwope, Axel D.; Thinius, Bernd D.We present time-resolved photometry of the cataclysmic variable PTF1J2224+17 obtained during four nights in October 2018 and January 2019 from Inastars observatory. The object is variable on a period of 103.82 min. Archival Catalina Real-Time Transient Survey (CRTS), Palomar Transient Factory, and Zwicky Transient Facility-data show frequent changes between high and low states. Based on its photometric properties and the cyclotron humps in the identification spectrum the object is certainly classified as an AM Herculis star (or polar) with a likely magnetic field strength of B∼65 MG. Its accretion duty cycle was estimated from 9 years of photometric monitoring to be about 35%.
- ItemNo further evidence for a transiting inner companion to the hot Jupiter HATS-50b(Berlin : Wiley-VCH Verl., 2019) Mallonn, MatthiasMost hot Jupiter exoplanets do not have a nearby planetary companion in their planetary system. One remarkable exception is the system of WASP-47 with an inner and outer nearby companion to a hot Jupiter, providing detailed constraints on its formation history. In this work, we follow up on a tentative photometric signal of a transiting inner companion to the hot Jupiter HATS-50 b. If confirmed, it would be the third case of a hot Jupiter with an inner companion. Sixty three hours of new ground-based photometry were employed to rule out this signal to about 96% confidence. The injection of artificial transit signals showed the data to be of sufficient quality to reveal the potential photometric feature at high significance. However, no transit signal was found. The discrete pattern of observing blocks leaves a slight chance that the transit was missed.
- ItemOn the parameter refinement of inflated exoplanets with large radius uncertainty based on TESS observations(Berlin : Wiley-VCH Verl., 2022) Alexoudi, XanthippiWe 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 (Formula presented.). 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.
- ItemMACHO 311.37557.169: A VY Scl star(Berlin : Wiley-VCH Verl., 2020) Wörpel, Hauke; Schwope, Axel D.; Traulsen, Iris; Brown, Michael J.I.Optical surveys, such as theMACHO project, often uncover variable stars whose classification requires follow-up observations by other instruments. We performed X-ray spectroscopy and photometry of the unusual variable starMACHO 311.37557.169 with XMM-Newton in April 2018, supplemented by archival X-ray and optical spectrographic data. The star has a bolometric X-ray luminosity of about 1 × 1032 erg s−1 cm−2 and a heavily absorbed two-temperature plasma spectrum. The shape of its light curve, its overall brightness, its X-ray spectrum, and the emission lines in its optical spectrum suggest that it is most likely a VY Scl cataclysmic variable.
- ItemOn the lithium abundance of the visual binary components ξ Boo A (G8V) and ξ Boo B (K5V)(Berlin : Wiley-VCH Verl., 2022) Strassmeier, Klaus G.; Steffen, MatthiasA spectroscopic investigation of the lithium resonance doublet in ξ Boo A and ξ Boo B in terms of both abundance and isotopic ratio is presented. We obtained new R = 130,000 spectra with a signal-to-noise ratio (S/N) per pixel of up to 3200 using the 11.8 m LBT and PEPSI. From fits with synthetic line profiles based on 1D-LTE MARCS model atmospheres and 3D-NLTE corrections, we determine the abundances of both isotopes. For ξ Boo A, we find A(Li) = 2.40 ± 0.03 dex and 6Li/7Li <1.5 ± 1.0% in 1D-LTE, which increases to ≈2.45 for the 3D-NLTE case. For ξ Boo B we obtain A(Li) = 0.37 ± 0.09 dex in 1D-LTE with an unspecified 6Li/7Li level. Therefore, no 6Li is seen on any of the two stars. We consider a spot model for the Li fit for ξ Boo B and find A(Li) = 0.45 ± 0.09 dex. The 7Li abundance is 23 times higher for ξ Boo A than the Sun's, but three times lower than the Sun's for ξ Boo B while both fit the trend of single stars in the similar-aged M35 open cluster. Effective temperatures are redetermined from the TiO band head strength. We note that the best-fit global metallicities are −0.13 ± 0.01 dex for ξ Boo A but +0.13 ± 0.02 dex for ξ Boo B. Lithium abundance for the K5V benchmark star 61 Cyg A was obtained to A(Li) ≈ 0.53 dex when including a spot model but to ≈0.15 dex without a spot model.
- ItemOn the binary orbit of Henry Draper one (HD 1)(Berlin : Wiley-VCH Verl., 2020) Strassmeier, Klaus G.; Weber, MichaelWe present our final orbit for the late-type spectroscopic binary Henry Draper one (HD 1). area total of 553 spectra from 13 years of observations are used with our robotic STELLA facility and its high-resolution echelle spectrograph SES. Its long-term radial velocity stability is ≈50 m s−1. A single radial velocity of HD 1 reached an rms residual of 63 m s−1, close to the expected precision. Spectral lines of HD 1 are rotationally broadened with a v sin i of 9.1±0.1 km s−1. The overall spectrum appears single-lined and yielded an orbit with an eccentricity of 0.5056±0.0005 and a semiamplitude of 4.44 km s−1. We constrain and refine the orbital period based on the SES data alone to 2, 318.70±0.32 days, compared to 2, 317.8±1.1 days when including the older dataset published by DAO and Cambridge/Coravel. Owing to the higher precision of the SES data, we base the orbit calculation only on the STELLA/SES velocities so as to not degrade its solution. We redetermine astrophysical parameters for HD 1 from spectrum synthesis and, together with the new Gaia DR-2 parallax, suggest a higher luminosity than published previously.We conclude thatHD1 is a slightly metal-deficient K0 III-II giant 217 times more luminous than the Sun. The secondary remains invisible at optical wavelengths. We present evidence for the existence of a third component.
- ItemAlpha tensor and dynamo excitation in turbulent fluids with anisotropic conductivity fluctuations(Berlin : Wiley-VCH Verl., 2023) Gressel, Oliver; Rüdiger, Günther; Elstner, DetlefA mean-field theory of the electrodynamics of a turbulent fluid is formulated under the assumption that the molecular electric conductivity is correlated with the turbulent velocity fluctuation in the (radial) direction, (Formula presented.). It is shown that for such homogeneous fluids a strong turbulence-induced field advection anti-parallel to (Formula presented.) arises almost independently of rotation. For rotating fluids, an extra (Formula presented.) effect appears with the known symmetries and with the expected maximum at the poles. Fast rotation, however, with Coriolis number exceeding unity suppresses this term. Numerical simulations of forced turbulence using the nirvana code demonstrate that the radial advection velocity, (Formula presented.), always dominates the (Formula presented.) term. We show finally with simplified models that (Formula presented.) dynamos are strongly influenced by the radial pumping: for (Formula presented.) the solutions become oscillatory, while for (Formula presented.) they become highly exotic if they exist at all. In conclusion, dynamo models for slow and fast solid-body rotation on the basis of finite conductivity–velocity correlations are unlikely to work, at least for (Formula presented.) dynamos without strong shear.