Nodal Precession and Tidal Evolution of Two Hot-Jupiters:WASP-33 b and KELT-9 b

Hot Jupiters orbiting rapidly rotating stars on inclined orbits undergo tidally induced nodal precession measurable over several years of observations. The Hot Jupiters WASP33 b and KELT9 b are particularly interesting targets as they are among the hottest planets found to date, orbiting relatively massive stars. Here, we analyze archival and new data that span 11 and 5 years for WASP33 b and KELT9 b, respectively, in order to to model and improve upon their tidal precession parameters. Our work confirms the nodal precession for WASP33 b and presents the first clear detection of the precession of KELT9 b. We determine that WASP33 and KELT9 have gravitational quadrupole moments. We estimate the planets’ precession periods to be 1460 years and 890 years, respectively, and that they will cease to transit their host stars around the years 2090CE and 2074CE, respectively. Additionally, we investigate both planets’ tidal and orbital evolution, suggesting that a higheccentricity tidal migration scenario is possible to produce both system architectures and that they will most likely not be engulfed by their hosts before the end of their main sequence lifetimes.

Modeling results for WASP-33 b data in 2016 (top panels from TULL; only one year shown), and 2019 (bottom panel; PEPSI). Left: Fourier-filtered residual map after subtracting the median line profile. The planet “Doppler shadow” is the diagonal blue track running from the bottom-right to the top-left. Occasional gaps are due to interpolation onto a time array with a fixed interval. Middle: Modeled Doppler Tomography signal. The overall gradient along the time axis is due to the shift of stellar radial velocity. The enhanced red background during transit is due to the fact that we set the line profile normalization to unity for all line profiles. Right: difference of the two maps on the left and middle panel.

Read more: Stephan et al. 2022, arXiv:2203.02546v1

Variable and Supersonic Winds in the Atmosphere of anUltrahot Giant Planet

Hot Jupiters receive intense irradiation from their stellar hosts. The resulting extreme environments in their atmospheres allow us to study the conditions that drive planetary atmospheric dynamics, e.g., globalscale winds. General circulation models predict daytonightside winds and equatorial jets with speeds of the order of a few km s1. To test these models, we apply highresolution transmission spectroscopy using the Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI) spectrograph on the Large Binocular Telescope to study the atmosphere of KELT9 b, an ultrahot Jupiter and currently the hottest known planet. We measure ~10 km s1 daytonightside winds traced by Fe II features in the planet’s atmosphere. This is at odds with previous literature (including data taken with PEPSI), which report no significant daytonightside winds on KELT9 b. We identify the cause of this discrepancy as due to an inaccurate ephemeris for KELT9 b in previous literature.

2D maps of transmission spectra, focusing on the six Fe II absorption lines in the PEPSI 2018 data set chosen for fitting Kp and v_wind. The blue track is the planet’s atmospheric absorption while the red track is the Doppler shadow from the RME; both tracks only form during a transit. Top panel displays fully in-transit observations. Middle panel shows the best-fit model from MCMC sampling. The bottom panel presents the residuals (data-model).

Read more: Pai Asnodkar et al. 2022, AJ, 163, 155

KELT-9 as an Eclipsing Double-lined Spectroscopic Binary: A Unique and Self-consistent Solution to the System

Transiting hot Jupiters present a unique opportunity to measure absolute planetary masses due to the magnitude of their radial velocity signals and known orbital inclination. Measuring planet mass is critical to understanding atmospheric dynamics and escape under extreme stellar irradiation. Here we present the ultrahot Jupiter system KELT-9 as a double-lined spectroscopic binary. This allows us to directly and empirically constrain the mass of the star and its planetary companion without reference to any theoretical stellar evolutionary models or empirical stellar scaling relations. Using data from the PEPSI, HARPS-N, and TRES spectrographs across multiple epochs, we apply least-squares deconvolution to measure out-of-transit stellar radial velocities. With the PEPSI and HARPS-N data sets, we measure in-transit planet radial velocities using transmission spectroscopy. By fitting the circular orbital solution that captures these Keplerian motions, we recover a planetary dynamical mass of 2.17 ± 0.56 MJ and stellar dynamical mass of 2.11 ± 0.78 M, both of which agree with the discovery paper. Furthermore, we argue that this system, as well as systems like it, are highly overconstrained, providing multiple independent avenues for empirically cross-validating model-independent solutions to the system parameters. We also discuss the implications of this revised mass for studies of atmospheric escape.

A 2D map of transmission spectra over the course of KELT-9 b’s transit for the PEPSI 2018 data set; the blue track is formed by the planet’s atmospheric absorption, while the red track is the Doppler shadow from the RME. The top panel displays fully in-transit observations. The middle panel shows the best-fit model from MCMC sampling, with the Doppler shadow and CLV determined from numerical modeling of the planet’s transit using SME stellar models, while the planet absorption track is a uniform Gaussian signal shifted in velocity according to the best-fit orbital motion of the planet, systemic velocity, and best-fit dayside-to-nightside winds. The bottom panel shows the residuals (data–model).

Read more: Pai Asnodkar et al. 2022, AJ, 163, 40P

Extremely slowly rotating magnetic O9.7V star HD54879

The O9.7 V star HD 54879 is currently the only massive magnetic star whose magnetic field geometry and rotation period are not constrained. Over the last three years, we gathered additional observations of this star, obtained using various instruments at several astronomical facilities with, the aim to constrain the rotation period and the magnetic field geometry. The new data include the first full Stokes vector observations with the PEPSI spectropolarimeter, installed at the Large Binocular Telescope. The acquired spectropolarimetric observations show a very slow magnetic field variability related to the extremely slow rotation of HD 54879, which is also indicated in a dynamical spectrum, displaying variability of the Hα line.

Generally, magnetic massive O- and B-type stars exhibit a smooth, single-wave variation of the longitudinal magnetic field during the stellar rotation cycle. The approximately sinusoidal variation of ⟨Bz⟩ and the ratio of the values of the ⟨Bz⟩ extrema in previously studied stars suggest that there is an important component of the field that is dipolar. Assuming that the magnetic field of HD 54879 has a pure dipolar configuration and that the negative field extremum is indeed around −570 G and not at a lower value, we fitted a cosine curve to the observed distribution of data points obtained from the high-resolution spectropolarimetric observations and determined a stellar rotation period of 7.2 yr. Certainly, further monitoring of the magnetic field variability is needed to determine the rotation period with more confidence. We note, that magnetic studies of several O-type stars indicate that only one magnetic pole is well visible while the star rotates, implying that the magnetic field structure over the fraction of their invisible surface remains unconstrained.

The four Stokes parameters and their null profiles for two individual lines, He I at 5875.6Å and S III at 5739.7Å, in PEPSI observations obtained on 2020 December 6. In the spectra recorded in circular polarized light, clear Zeeman signatures are detected for both lines whereas the spectra recorded in linear polarized light appear flat.

Read more: Järvinen et al. 2022, MNRAS, 501, 4405. arXiv

The rapidly oscillating Ap star γ Equ: linear polarization as an enhanced pulsation diagnostic?

We present the first short time scale observations of the roAp star γ Equ in linear polarized light obtained with the PEPSI polarimeter installed at the LBT. These observations are used to search for pulsation variability in Stokes Q and U line profiles belonging to different elements. The atmospheres of roAp stars are significantly stratified with spectral lines of different elements probing different atmospheric depths. roAp stars with strong magnetic fields, such as γ Equ with a magnetic field modulus of 4 kG and a pulsation period of 12.21 min, are of special interest because the effect of the magnetic field on the structure of their atmospheres can be studied with greatest detail and accuracy. Our results show that we may detect changes in the transversal field component in Fe I and rare-earth lines possessing large second-order Landé factors. Such variability can be due to the impact of pulsation on the transverse magnetic field, causing changes in the obliquity angles of the magnetic force lines. Further studies of roAp stars in linear polarized light and subsequent detailed modelling are necessary to improve our understanding of the involved physics.

Variabi;ity detected in linear polarization profiles.
Zeeman signatures of γ Equ in the linear polarization line profiles of different lines recorded with PEPSI on two different pulsation phases in 2017 September 11. Individual and overplotted Stokes I profiles for single and LSD profiles are shown in the bottom panels followed by individual and overplotted Stokes Q and U profiles in the middle panels. The upper panels present the differences between the Stokes Q and U profiles with the associated error bars. Since the spectral resolution of R ∼ 130 000 offered by the PEPSI observations is sampled by 4.2 CCD pixels, to achieve a higher S/N, the Stokes Q and U spectra have been smoothed using Gaussians.


Read more: Hubrig et al. 2021, MNRAS 508 L17. arXiv:2108.11272

Searching For Transiting Planets Around Halo Stars. I. Sample Selection and Validation

By measuring the elemental abundances of a star, we can gain insight into the composition of its initial gas cloud — the formation site of the star and its planets. Planet formation requires metals, the availability of which is determined by the elemental abundance. In the case where metals are extremely deficient, planet formation can be stifled. To investigate such a scenario requires a large sample of metal-poor stars and a search for planets therein. This paper focuses on the selection and validation of a halo star sample. We select ~17,000 metal-poor halo stars based on their Galactic kinematics, and confirm their low metallicities ([Fe/H] < -0.5), using spectroscopy from the literature. Furthermore, we perform high-resolution spectroscopic observations using LBT/PEPSI and conduct detailed metallicity ([Fe/H]) analyses on a sample of 13 previously known halo stars that also have hot kinematics. We can use the halo star sample presented here to measure the frequency of planets and to test planet formation in extremely metal-poor environments.

A range of the PEPSI B-band spectrum of HD 160693, with iron line features annotated with their corresponding equivalent width.

Read more: Kolecki et al. 2021, AJ, 162, 125. arXiv:2106.13251

Time-resolved rotational velocities in the upper atmosphere of WASP-33 b

While steady empirical progress has been made in understanding the structure and composition of hot planet atmospheres, direct measurements of velocity signatures, including winds, rotation, and jets, have lagged behind. Quantifying atmospheric dynamics of hot planets is critical to a complete understanding of their atmospheres and such measurements may even illuminate other planetary properties, such as magnetic field strengths. In this manuscript, we present the first detection of the Balmer lines H-alpha and H-beta in the atmosphere of the ultra-hot Jupiter WASP-33b. Using atmospheric models which include the effects of atmospheric dynamics, we show that the shape of the average Balmer line transmission spectrum is consistent with rotational velocities in the planet’s thermosphere of vrot = 10.1 (+0.8 -1.0) km/s. We also measure a low-significance day-to-night side velocity shift of -4.6 +/-3.4 km/s in the transmission spectrum which is naturally explained by a global wind across the planet’s terminator. In a separate analysis the time-resolved velocity centroids of individual transmission spectra show unambiguous evidence of rotation, with a best-fit velocity of 10.0 (+2.4 -2.0) km/s, consistent with the value of vrot derived from the shape of the average Balmer line transmission spectrum. Our observations and analysis confirm the power of high signal-to-noise, time resolved transmission spectra to measure the velocity structures in exoplanet atmospheres. The large rotational and wind velocities we measure highlight the need for more detailed 3D global climate simulations of the rareed upper-atmospheres of ultra-hot gas giants.

Spectral map of the H-alpha and H beta transmission spectra in the stellar rest frame for the entire night. The spectra have been interpolated onto an evenly spaced time vector for display purposes which produces some of the smearing near the beginning and end of the night when exposures were longer on average. The transit contact points T1 and T4 are shown with horizontal purple lines. The star’s  vsini value is marked with the vertical green lines. The planet’s line-of-sight velocity is shown with the blue line. There is a clear H-alpha signature which moves along the planet’s velocity for the duration of the transit. The H-beta absorption is weaker but still present at the expected velocities. Note the pulsation stripes visible in the pre transit data in both lines.

Read more: Cauley et al. 2021, AJ, 161, 152

A Unicorn in Monoceros: the 3M⊙ dark companion to the bright, nearby red giant V723 Mon is a non-interacting, mass-gap black hole candidate

We report the discovery of the closest known black hole candidate as a binary companion to V723 Mon. V723 Mon is a nearby (d=460 pc), bright evolved red giant in a high mass function nearly circular binary (𝑃 = 59•.9 d, e approx. 0). Analyses of the stellar spectra and spectral energy distribution (SED) give 𝑇eff =– 4440 K, 𝐿 = 173 𝐿s and 𝑅 = 22 𝑅. Matching these parameters to MIST evolutionary models indicates a mass of the visible giant of 𝑀giant = 1.•07 +/- 0.•24 𝑀. V723 Mon is a known variable star, previously classified as an eclipsing binary, but its All-Sky Automated Survey (ASAS), Kilodegree Extremely Little Telescope (KELT), and Transiting Exoplanet Survey Satellite (TESS) light curves are those of a nearly edge-on ellipsoidal variable. Detailed models of the light curves constrained by the period, radial velocities and stellar temperature give an inclination of 𝑖 = 87• deg, a mass ratio of 0•.30 +/- 0•.02, and a  companion mass of 𝑀comp = 2.•91 +/- 0•.08 𝑀, a stellar radius of the giant of 𝑅giant = 23.•6 +/-1.•0 𝑅, and a giant mass of 𝑀giant = 0.•87 +/-0.•08 𝑀 , consistent with our other estimates. We identify a likely non-stellar, diffuse veiling component with contributions in the 𝐵 and 𝑉-band of ~64% and ~23%, respectively, and a luminosity of ~20 𝐿. The SED and the absence of continuum eclipses imply that the companion mass must be dominated by a compact object even if the companion is a binary. We do observe eclipses of the Balmer lines when the dark companion passes behind the giant, but their velocity spreads are low compared to observed accretion disks. The X-ray luminosity of the system is 𝐿X = 1• x 10^30 erg/s, corresponding to 𝐿/𝐿edd ~10^-9. The simplest explanation for the massive companion is a single compact object, most likely a black hole in the “mass gap”, although a double neutron star binary is possible.

LBT/PEPSI line profiles for the Balmer H𝛼, H𝛽, Ca I 𝜆6439 and Ca I 𝜆6463 lines (black). A model spectrum using the atmospheric parameters is shown in red. The blue lines show the velocity offset of the Balmer absorption lines (12 km/s) from the rest frame of the giant. PEPSI was used in its R=250,000 resolution mode.

Read more: Jayasinghe et al. 2021, MNRAS, 504, 2577

Strongly magnetic Of?p star NGC 1624-2

NGC 1624-2 is an O7f?p star with a reported probable polar magnetic field strength ≥20 kG, which is the strongest magnetic field ever measured in an O-type star. We study the variability of the mean longitudinal magnetic field <Bz> and the mean field modulus to obtain constraints on its field geometry. Only one magnetic pole is observable over the rotation cycle. The approximately sinusoidal variation of <Bz> and the ratio of the values of the extrema of indicate that there is an important component of the field that is dipolar. The <Bz> values measured over the rotation cycle are in the range from -0.2 to 4.5 kG, whereas the values for vary between 9 and 12 kG. The <Bz> values obtained using the O III λ7455 emission line are in the range from 0.4 to 2.3 kG and show a variability pattern similar to that detected for the absorption lines. The fact that the phase of the <Bz> minimum coincides with the phase of the maximum, indicates that the field structure must significantly depart from a centred dipole. Further, we discuss the nature of the observed variable Stokes V profiles corresponding to a longitudinal field of negative polarity detected in the emission He I lines and present the first magnetohydrodynamical numerical simulations of the gas flow in the magnetosphere of this star.

The split components of the magnetically resolved line C IV λ5812.

Read more: Järvinen et al., 2021, MNRAS, 501, 4534, in arXiv

Mono-enriched stars and Galactic chemical evolution — Possible biases in observations and theory

A long sought after goal using chemical abundance patterns derived from metal-poor stars is to understand the chemical evolution of the Galaxy and to pin down the nature of the first stars (Pop III). Metal-poor, old, unevolved stars are excellent tracers as they preserve the abundance pattern of the gas from which they were born, and hence they are frequently targeted in chemical tagging studies. Here, we use a sample of 14 metal-poor stars observed with the high-resolution spectrograph called the Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI) at the Large Binocular Telescope (LBT) to derive abundances of 32 elements (34 including upper limits). We present well-sampled abundance patterns for all stars obtained using local thermodynamic equilibrium (LTE) radiative transfer codes and one-dimensional (1D) hydrostatic model atmospheres. However, it is currently well-known that the assumptions of 1D and LTE may hide several issues, thereby introducing biases in our interpretation as to the nature of the first stars and the chemical evolution of the Galaxy. Hence, we use non-LTE (NLTE) and correct the abundances using three-dimensional (3D) model atmospheres to present a physically more reliable pattern. In order to infer the nature of the first stars, we compare unevolved, cool stars, which have been enriched by a single event (‘mono-enriched’), with a set of yield predictions to pin down the mass and energy of the Pop III progenitor. To date, only few bona fide second generation stars that are mono-enriched are known. A simple χ 2 -fit may bias our inferred mass and energy just as much as the simple 1D LTE abundance pattern, and we therefore carried out our study with an improved fitting technique considering dilution and mixing. Our sample presents Carbon Enhanced Metal-Poor (CEMP) stars, some of which are promising bona fide second generation (mono-enriched) stars. The unevolved, dwarf BD+09_2190 shows a mono-enriched signature which, combined with kinematical data, indicates that it moves in the outer halo and likely has been accreted onto the Milky Way early on. The Pop III progenitor was likely of 25.5 M and 0.6 foe (0.6 1051 erg) in LTE and 19.2 M and 1.5 foe in NLTE, respectively. Finally, we explore the predominant donor and formation site of the rapid and slow neutron-capture elements.

Spectrum synthesis of C, Sm, (Nd), Dy, and Rb in various sample stars. Specifically, molecular and atomic C in TYC5481. We note that [C i/Fe] = 0.6±0.1; [CH/Fe] = 0.1 ± 0.1; in BD-0.1_2439, [Sm/Fe] = 0.3 ± 0.1 and the shown Nd line was not used in our average Nd value due to blends and a poor fit – synthesis shows [Nd/Fe] = 0.3, 0.8, 0.9; [Dy/Fe] = 0.5 ± 0.1; and in HD136343, [Rb/Fe] = 0.4 ± 0.1. In all cases, the green dashed line indicates [X/Fe] = −5.


Read more:  Hansen et al. 2020, A&A, 643A, 49, in arXiv