The Pepsi Exoplanet Transit Survey (PETS@LBT) Workshop is scheduled on
Tuesday Sep 22 – 6am to 9am AZ time (13:00-16:00 UTC)
In this Workshop, we will discuss and wrap-up our community proposal for a large LBT program, to be submitted shortly thereafter. We propose a high-resolution spectroscopic survey of exoplanet transits, secondary eclipses, and host-star characterizations of selected targets; dubbed the “PEPSI/LBT Exoplanet Transit Survey (PETS)”. Immediate goal is characterizing the planetary and stellar atmospheres in detail. During this 3-hr Zoom meeting we shall emphasis again the strengths and uniqueness of this proposal and recall shortcomings. The survey requests 40 nights in total or 12.5 nights per semester for two years in order to observe a representative number of targets starting in semester 2021A.
Comparing chemical abundances of a planet and the host star reveals the origin and formation pathway of the planet. Stellar abundance is measured with high-resolution spectroscopy. Planet abundance, on the other hand, is usually inferred from low-resolution data. For directly imaged exoplanets, the data are available from a slew of high-contrast imaging/spectroscopy instruments. Here, we study the chemical abundance of HR 8799 and its planet c. We measure stellar abundance using LBT/PEPSI (R=120,000) and archival HARPS data: stellar [C/H], [O/H], and C/O are 0.11±0.12, 0.12±0.14, and 0.54+0.09-0.12, all consistent with solar values. We conduct atmospheric retrieval using newly obtained Subaru/CHARIS data together with archival Gemini/GPI and Keck/OSIRIS data. We model the planet spectrum with petitRADTRANS and conduct retrieval using PyMultiNest. Retrieved planetary abundance can vary by ∼0.5 dex, from sub-stellar to stellar C and O abundances. The variation depends on whether strong priors are chosen to ensure a reasonable planet mass. Moreover, comparison with previous works also reveals inconsistency in abundance measurements. We discuss potential issues that can cause the inconsistency, e.g., systematics in individual data sets and different assumptions in the physics and chemistry in retrieval. We conclude that no robust retrieval can be obtained unless the issues are fully resolved.
Gaia benchmark stars are selected to be calibration stars for different spectroscopic surveys. Very high-quality and homogeneous spectroscopic data for these stars are therefore required. We collected ultrahigh-resolution ESPRESSO spectra for 30 of the 34 Gaia benchmark stars and made them public. We quantify the consistency of the results that are obtained with different high-, and ultrahigh-resolution spectrographs. We also comprehensively studied the effect of using different spectral reduction products of ESPRESSO on the final spectroscopic results. We used ultrahigh- and high-resolution spectra obtained with the ESPRESSO, PEPSI, and HARPS spectrographs to measure spectral line characteristics (line depth; line width; and EW) and determined stellar parameters and abundances for a subset of 11 Gaia benchmark stars. The EW spectral line measurements based on the ESPRESSO, PEPSI, and HARPS spectra agree to within a few percent. However, we note that the lines appear deeper in the ESPRESSO spectra than in PEPSI and HARPS. The stellar parameters derived from each spectrograph by combining the several available spectra agree well overall. We conclude that the ESPRESSO, PEPSI, and HARPS spectrographs can deliver spectroscopic results that are sufficiently consistent for most of the science cases in stellar spectroscopy.
A team around Engin Keles (AIP) compared previously observed high resolution Na I and K I absorption in the atmosphere of HD189733b with synthetic transmission spectra modeled for a variety of temperature and abundance values. The comparison showed that the observed Na I-D-line widths are much larger than the modeled ones. The Na I-D-lines had to be broadened by velocities in the order of 10 km/s to match the observations if only rotational broadening is taken into account. The K I line profile on the other hand showed only a few km/s broadening comparable with the synthetic line profiles. This hints that either the atmosphere of HD 189733b lacks a significant amount of K I or the alkali lines probe different atmospheric regions with different temperature, which could explain the differences in the resolved absorption lines.
T Coronae Borealis is a recurrent, symbiotic nova system currently in quiescence between its periodic ≍80 yr cycle of eruptions. Observations during inter-outburst epochs provide an opportunity to study properties of the accretion disk and the M red giant. Here we present new irradiated (blackbody veiling) models, incorporating modern molecular opacities and line lists, of spectra derived from high-resolution (22,000 ≲ R ≲ 120,000) optical echelle observations obtained at two epochs, one prior to and one post the 2015 rebrightening event at similar spectroscopic system phase. We find a lithium abundance in the secondary at both epochs to be comparable. The non-irradiated (classical) model atmospheres yield a lithium abundance, A(Li) = 1.3 ± 0.1. The irradiated model (veiled) atmospheres, which are likely a better representation of the system in which the white dwarf and accretion disk illuminate the red giant, give A(Li) = 2.4 ± 0.1.
January 2019 featured a total lunar eclipse. The Moon dimmed by a factor of 20,000 (10.75 mag) during totality. Therefore, the light gathering capability of the 11.8 m Large Binocular Telescope (LBT) in Arizona was needed for the observations. Additionally, the high spectral resolution of the Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI) was necessary to separate the expected tiny spectral-line absorptions of the Earth’s atmosphere from the normal solar spectrum at unprecedented spectral resolution and in polarized light. The radial velocities trace a wavelength dependent Rossiter-McLaughlin effect of the Earth eclipsing the Sun as seen from the Tycho crater confirming earlier observations. No line polarization of any spectral-line feature is detected outside nor inside eclipse. This places an upper limit of ≈0.2% on the degree of line polarization during transmission through Earth’s atmosphere and magnetosphere.
LBT/PEPSI spectropolarimetry tested the hypothesis that the surface magnetic morphology is a crucial component for the spin down of stars. Solar-type stars are born with relatively rapid rotation and strong magnetic fields. Through a process known as magnetic braking, the rotation slows over time as stellar winds gradually remove angular momentum from the system. The rate of angular momentum loss depends sensitively on the magnetic morphology, with the dipole field exerting the largest torque on the star. One hypothesis to explain this reduction in efficiency is a shift in magnetic morphology from predominantly larger to smaller spatial scales. We tested this hypothesis with spectropolarimetric measurements of two stars that sample chromospheric activity levels on opposite sides of the proposed magnetic transition. As predicted, the more active star (HD 100180) exhibits a significant circular polarization signature due to a non-axisymmetric large-scale magnetic field, while the less active star (HD 143761) shows no significant signal.
We investigated the potassium excess absorption around 7699 Å of the exoplanets HD189733b and HD209458b using high-spectral resolution transit observations acquired with the 2 × 8.4 m Large Binocular Telescope (LBT) and the Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI). For a bandwidth of 0.8 Å, we present a detection >7σ with an absorption level of 0.18 per cent for HD189733b. Applying the same analysis to HD209458b, we can set 3σ upper limit of 0.09 per cent, even though a K-excess absorption was not detected. The investigation suggests that the K feature is less present in the atmosphere of HD209458b than in the one of HD189733b and confirms previous claims that the atmospheres of these two planets must have fundamentally different properties.
We present a temperature and a magnetic-field surface map of the K2 subgiant of the active binary II Peg. Employed are high resolution Stokes IV spectra obtained with the new Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI) at the Large Binocular Telescope (LBT). Our main result is that the temperature features on II Peg closely correlate with its magnetic field topology. We find a warm spot (350K warmer with respect to the effective temperature) of positive polarity and radial field density of 1.1 kG coexisting with a cool spot (780K cooler) of negative polarity of 2 kG.
The 33 meters long (in A0 format) spectrum of epsilon Eridani is available for download. See the Wallposters section among the Library links. Note that the whole spectrum is in two PDF files, each having a size of almost 18 MB.