The solar eclipse of 2017 August 21 was observed with the Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI) on the Large Binocular Telescope (LBT), which is located at Mt. Graham International Observatory (MGIO), Arizona, USA. At this location, a partial eclipse was observed with maximum obscuration of 61.6%. The 11-millimeter-aperture, binocular Solar Disk-Integrated (SDI) telescope, located on the kitchen balcony of the LBT building, feeds sunlight to PEPSI, which has recorded a total of 116 Sun-as-a-star spectra in the wavelength range of 5300 – 6300 Å, with a spectral resolution R=250,000 and S/N of about 733:1. The temporal evolution of the Fraunhofer Na I D doublet at 5890/5896 Å is analyzed using contrast profiles that illustrate subtle changes in the spectral line, not obvious in the intensity profiles.
Time-series of the radial velocity obtained from the Na D2 (blue) and Na D1 (red) lines observed during solar eclipse. The vertical lines indicate the time of maximum obscuration. The line-core velocities (top-left) are computed from a parabola fit to the line core, whereas the line-wing velocities reflect bisector velocities at certain distances from the line core, which are given in milli-Ångstrom in the lower-right corner of each panel. The relative formation heights are given in the corresponding color in the lower-left corner of each panel.
We present an atmospheric retrieval analysis on a set of young, cloudy, red L dwarfs—CWISER J124332.12+600126.2 (BD+60 1417B) and WISEP J004701.06+680352.1 (W0047)—using the Brewster retrieval framework. We also present the first elemental abundance measurements of the young K-dwarf (K0) host star, BD+60 1417, using high-resolution (R = 50,000) spectra taken with the Potsdam Echelle Polarimetric and Spectroscopic Instrument on the Large Binocular Telescope. In the complex cloudy L-dwarf regime the emergence of condensate cloud species complicates retrieval analysis when only near-infrared data are available. We find that for both L dwarfs in this work, despite testing three different thermal profile parameterizations we are unable to constrain reliable abundance measurements and thus the carbon-to-oxygen ratio. While we cannot conclude what the abundances are, we can conclude that the data strongly favor a cloud model over a cloudless model. We note that the difficulty in retrieval constraints persists regardless of the signal-to-noise ratio of the data examined (S/N ∼ 10 for CWISER BD+60 1417B and 40 for WISEP W0047). The results presented in this work provide valuable lessons about retrieving young, low-surface-gravity cloudy L dwarfs. This work provides continued evidence of missing information in models and the crucial need for JWST to guide and inform retrieval analysis in this regime.
PEPSI spectra of BD+60 1417 in selected wavelength regions of 7687–7695 Å (left), 7770–7778 Å (center), and 8770–8777 Å (right). Line features used in the abundance analysis have been labeled.
We introduce a new solar feed for the PEPSI nighttime spectrograph of the LBT. It enables spectroscopy of the Sun-as-a-star in circular polarization (CP) and linear polarization (LP) with a spectral resolution of 250,000 (≈0.025 Å or 600 m s−1) for the wavelength range 383–907 nm. The polarimeter is a dual-beam design with a modified Wollaston prism as beam splitter and linear polarizer combined with a retractable super-achromatic 𝜆∕4 retarder. The Wollaston beam diameter is 14 mm and large enough that it does not require a classical telescopic feed anymore. Both polarimetric beams are re-imaged into respective integration spheres from which two fibers feed the scrambled light to the spectrograph. The system is fully automated in the sense that it finds the Sun in the morning, closes the guider loop, observes a predefined number of individual spectra, and moves to a home position at the end of the day. Among the scientific aims is Zeeman–Doppler imaging of the Sun as a star over the next activity cycle. Our first-light application detects a clear Stokes-V/I profile with a full amplitude of 1 × 10-4 on, for example, October 13, 2023, suggesting a solar disk-averaged line-of-sight net magnetic field of +0.37±0.02 G. Comparison of this value with a contemporary full-disk line-of-sight magnetogram suggests an unsigned mean field of about ≈13 G.
Full facility close up. (a) CAD sketch. Shown are the polarimeter unit, its PlaneWave alt-az mount, the pier, and the Baader AllSky dome. The light-entrance baffle sticks out of the main polarimeter box and points in the south direction. (b) As built. In this picture the telescope points in the east direction shortly after sunrise. Notice the small circular opening in the box to the top right of the baffle, which is the guider telescope.
The time variability and spectra of directly imaged companions provide insight into their physical properties and atmospheric dynamics. We find an effective temperature Teff = 2794+115−133 K on the first night, consistent with the literature, but a cooler Teff = 2279+79−157 K on the next. We estimate the mass of HD 1160 B to be 16-81 MJup, depending on its age. We also present R = 50 000 high-resolution optical spectroscopy of host star HD 1160 A obtained simultaneously with the PEPSI spectrograph. We reclassify its spectral type to A1 IV-V and measure its projected rotational velocity vsini = 96+6−4 km s-1. We thus highlight that gvAPP-enabled differential spectrophotometry can achieve repeatable few per cent level precision and does not yet reach a systematic noise floor, suggesting greater precision is achievable with additional data or advanced detrending techniques.
The left panel shows the PEPSI spectrum of the host star HD 1160 A in blue, overplotted with the best-fitting model from BT-Nextgen in orange. The fitting process was carried out for the region of the spectrum covering 392–429 nm. The contour plot in the right panel shows the χ2 distribution for several temperatures and vsini at fixed log(g) of 3.5.
Absorption lines from exoplanet atmospheres observed in transmission allow us to study atmospheric characteristics such as winds. We present a new high-resolution transit time-series of HD 189733b, acquired with the PEPSI instrument at the LBT and analyse the transmission spectrum around the Na D lines. We model the spectral signature of the RM-CLV-effect using synthetic PHOENIX spectra based on spherical LTE atmospheric models. We find an Na D absorption signature between the second and third contact but not during the ingress and egress phases, which casts doubt on the planetary origin of the signal. Presupposing a planetary origin of the signal, the results suggest a weak day-to-nightside streaming wind in the order of 0.7 km/s and a moderate super-rotational streaming wind in the order of 3-4 km/s, challenging claims of prevailing strong winds on HD 189733b.
The HD 189733b transit observation. Top: Continuum signal-to-noise ratio per combined pixel (95 per cent quantile). Bottom: The RM effect. Dashed vertical lines show the contact points 1st–4th (cyan) and 2nd–3rd (purple).
Pulsations of rapidly oscillating Ap stars and their interaction with the stellar magnetic field have not been studied in the near-infrared (near-IR) region despite the benefits these observations offer compared to visual wavelengths. The main advantage of the near-IR is the quadratic dependence of the Zeeman effect on the wavelength, as opposed to the linear dependence of the Doppler effect.
To test pulsation diagnostics of roAp stars in the near-IR, we investigated the pulsation behaviour of one of the brightest magnetic roAp stars, γ Equ, which possesses a strong surface magnetic field of the order of several kilogauss and exhibits magnetically split spectral lines in its spectra.
The profile shapes of both studied magnetically split spectral lines in H-band vary in a rather complex manner probably due to a significant decrease in the strength of the longitudinal field component and an increase in the strength of the transverse field components over the last decade. A mean magnetic field modulus of 3.9 kG was determined for the Zeeman triplet Fe I at 1563.63 nm, whereas for the pseudo- doublet Ce III at 1629.2 nm we observe a much lower value of only about 2.9 kG. For comparison, a mean field modulus of 3.4 kG was determined using the Zeeman doublet Fe II at 6249.25 Å in optical PEPSI spectra recorded just about two weeks before the 2022 CRIRES+ observations. Different effects may lead to the differences in the field modulus values. The measurements of the mean magnetic field modulus in different pulsational phase bins suggest a field modulus variability of 32 G for the Zeeman triplet Fe I and 102 G for the pseudo-doublet Ce III.
Zeeman doublet Fe II at 6149.25 Å used for measuring the mean magnetic field modulus in observations obtained in different years using different instruments. Right: Comparison of the shape of line profiles of Zeeman triplet Fe I 1563.63 nm from different years in near-IR region.
The consistently low activity level of the old solar analog 51 Peg not only facilitated the discovery of the first hot Jupiter, but also led to the suggestion that the star could be experiencing a magnetic grand minimum. However, the 50 yr time series showing minimal chromospheric variability could also be associated with the onset of weakened magnetic braking (WMB), where sufficiently slow rotation disrupts cycling activity and the production of large scale magnetic fields by the stellar dynamo, thereby shrinking the Alfvén radius and inhibiting the efficient loss of angular momentum to magnetized stellar winds. In this Letter, we evaluate the magnetic evolutionary state of 51 Peg by estimating its wind braking torque. We use new spectropolarimetric measurements from the Large Binocular Telescope to reconstruct the large-scale magnetic morphology, we reanalyze archival X-ray measurements to estimate the mass-loss rate, and we detect solar-like oscillations in photometry from the Transiting Exoplanet Survey Satellite, yielding precise stellar properties from asteroseismology. Our estimate of the wind braking torque for 51 Peg clearly places it in the WMB regime, driven by changes in the mass-loss rate and the magnetic field strength and morphology that substantially exceed theoretical expectations. Although our revised stellar properties have minimal consequences for the characterization of the exoplanet, they have interesting implications for the current space weather environment of the system.
ZDI maps of the radial, meridional, and azimuthal field components of 51 Peg. Contours are shown with a step of 0.5 G. The dotted line corresponds to the lowest visible latitude. The vertical bars at the bottom of each panel show the central longitude of each LBT observation.
Most ultra hot Jupiters (UHJs) show evidence of temperature inversions, in which temperature increases with altitude over a range of pressures. Temperature inversions can occur when there is a species that absorbs the stellar irradiation at a relatively high level of the atmospheres. However, the species responsible for this absorption remains unidentified. In particular, the UHJ KELT-20b is known to have a temperature inversion. Using high resolution emission spectroscopy from LBT/PEPSI we investigate the atomic and molecular opacity sources that may cause the inversion in KELT-20b, as well as explore its atmospheric chemistry. We confirm the presence of Fe I with a significance of 17𝜎. We also report a tentative 4.3𝜎 detection of Ni I. A nominally 4.5𝜎 detection of Mg I emission in the PEPSI blue arm is likely in fact due to aliasing between the Mg I cross-correlation template and the Fe I lines present in the spectrum. We cannot reproduce a recent detection of Cr I, while we do not have the wavelength coverage to robustly test past detections of Fe II and Si I. Together with non-detections of molecular species like TiO, this suggests that Fe I is likely to be the dominant optical opacity source in the dayside atmosphere of KELT-20b and may be responsible for the temperature inversion. We explore ways to reconcile the differences between our results and those in literature and point to future paths to understand atmospheric variability.
Shifted and combined cross correlation function (CCF, left) and injection-recovery test (right) for Ni I. This 4.3𝜎 detection falls within our tentative detection range. The vertical and horizontal dashed lines in all CCF maps represent the 𝐾𝑝 (radial velocity semi amplitude of the planet) and 𝑣𝑠𝑦𝑠 (system radial velocity) parameters for which we should expect to find a signal.
Read more: Petz, S., Johnson, M., Asnodkar, A. P. et al. 2023, MNRAS, in press (arXiv:2301.09352)
The bright star lam Ser hosts a hot Neptune with a minimum mass of 13.6 MEarth and a 15.5 day orbit. It also appears to be a solar analog, with a mean rotation period of 25.8 days and surface differential rotation very similar to the Sun. We detect solar-like oscillations in time series photometry from the Transiting Exoplanet Survey Satellite (TESS), and we derive precise asteroseismic properties from detailed modeling. We obtain new spectropolarimetric data, and we use them to reconstruct the large-scale magnetic field morphology. We reanalyze the complete time series of chromospheric activity measurements from the Mount Wilson Observatory, and we present new X-ray and ultraviolet observations from the Chandra and Hubble space telescopes. Finally, we use the updated observational constraints to assess the rotational history of the star and to estimate the wind braking torque. We conclude that the remaining uncertainty on stellar age currently prevents an unambiguous interpretation of the properties of lam Ser, and that the rate of angular momentum loss appears to be higher than for other stars with similar Rossby number. Future asteroseismic observations may help to improve the precision of the stellar age.
Stokes V polarization profile for lam Ser from PEPSI/LBT observations on 2021 May 24. The mean profile is shown as a black line, with uncertainties indicated by the gray shaded area. The red and blue lines are model profiles assuming dipole geometry and fixed inclination i = 50 degrees with different obliquity angles beta.
Read more: Metcalfe et al. 2023, AJ, in press (arXiv 2308.09808).
Numerous δ Sct and γ Dor pulsators are identified in the region of the Hertzsprung-Russell diagram that is occupied by chemically peculiar magnetic Ap stars. The connection between δ Sct and γ Dor pulsations and the magnetic field in Ap stars is however not clear: theory suggests for magnetic Ap stars some critical field strengths for pulsation mode suppression by computing the magnetic damping effect for selected p and g modes. To test these theoretical considerations, we obtained PEPSI spectropolarimetric snapshots of the typical Ap star HD 340577, for which δ Sct- like pulsations were recently detected in TESS data, and the γ Dor pulsator HR 8799, which is a remarkable system with multiple planets and two debris disks. Our measurements reveal the presence of a magnetic field with a strength of several hundred Gauss in HD 340577. The measured mean longitudinal field would be the strongest field measured so far in a δ Sct star if the pulsational character of HD 340577 is confirmed spectroscopically. No magnetic field is detected in HR 8799.
LSD Stokes I, V, and diagnostic null N spectra (from bottom to top) calculated for HD340577, for the mask with all lines and the masks for individual ions. The numbers in brackets relate to the number of lines used in each individual mask. The grey horizontal lines in the Stokes V and N spectra indicate the ±1σ error bars. Stokes V spectra are highlighted in red.
