All posts by Silva Järvinen

The Origin of Weakened Magnetic Braking in Old Solar Analogs

The rotation rates of main-sequence stars slow over time as they gradually lose angular momentum to their magnetized stellar winds. The rate of angular momentum loss depends on the strength and morphology of the magnetic field, the mass-loss rate, and the stellar rotation period, mass, and radius. Previous observations suggested a shift in magnetic morphology between two F-type stars with similar rotation rates but very different ages (88 Leo and ρ CrB). In this Letter, we identify a comparable transition in an evolutionary sequence of solar analogs with ages between 2–7 Gyr. We present new spectropolarimetry of 18 Sco and 16 Cyg A & B from the Large Binocular Telescope, and we reanalyze previously published Zeeman Doppler images of HD 76151 and 18 Sco, providing additional constraints on the nature and timing of this transition.

Stokes V circular polarization profiles for 18 Sco (left) and 16 Cyg A & B (right) from LBT PEPSI observations in 2021 May. Mean profiles are shown as black lines, while uncertainties are indicated with gray shaded areas. Colored lines show axisymmetric model profiles assuming dipole (blue), quadrupole (red), or octupole (magenta) geometry with fixed inclination.

Read more: Metcalfe et al. 2022, ApJ Letter, 933, 17; arXiv 2206.08540

An Aligned Orbit for the Young Planet V1298 Tau b

The alignment of planetary orbits with respect to the stellar rotation preserves information on their dynamical histories. Measuring this angle for young planets helps illuminate the mechanisms that create misaligned orbits for older planets, as different processes could operate over timescales ranging from a few megayears to a gigayear. We present spectroscopic transit observations of the young exoplanet V1298 Tau b; we update the age of V1298 Tau to be 28 ± 4 Myr based on Gaia EDR3 measurements. We observed a partial transit with Keck/HIRES and LBT/PEPSI, and detected the radial velocity anomaly due to the Rossiter-McLaughlin effect. V1298 Tau b has a prograde, well-aligned orbit, with λ=4+7−10 deg. By combining the spectroscopically measured vsini⋆ and the photometrically measured rotation period of the host star we also find that the orbit is aligned in 3D, ψ=8+4−7 deg. Finally, we combine our obliquity constraints with a previous measurement for the interior planet V1298 Tau c to constrain the mutual inclination between the two planets to be i mut = 0° ± 19°.

Doppler tomographic data from PEPSI (top three panels) and HIRES (bottom). All plots show the time-series line profile residuals, i.e., each horizontal line shows the deviation of the line profile from the average line profile at that time. Time increases from bottom to top; units are such that ingress = 0 and egress = 1. The vertical dotted lines show v = 0, ±$v sin i_star, the horizontal dotted line the time of mid-transit, and the two small plus signs first and second contact. In the HIRES plot we also show two slanted dotted lines to guide the eye along the spot signatures, which are less obvious than in the PEPSI data.

Read more:  Johnson et al. 2022, AJ, 163, 247

The PEPSI exoplanet transit survey (PETS) I: Investigating the presence of a silicate atmosphere on the super-earth 55 Cnc e

The study of exoplanets and especially their atmospheres can reveal key insights on their evolution by identifying specific atmospheric species. For such atmospheric investigations, highresolution transmission spectroscopy has shown great success, especially for Jupitertype planets. Towards the atmospheric characterization of smaller planets, the superEarth exoplanet 55 Cnc e is one of the most promising terrestrial exoplanets studied to date. Here, we present a highresolution spectroscopic transit observation of this planet, acquired with the PEPSI instrument at the Large Binocular Telescope. Assuming the presence of Earthlike crust species on the surface of 55 Cnc e, from which a possible silicatevapor atmosphere could have originated, we search in its transmission spectrum for absorption of various atomic and ionized species such as Fe , Fe +, Ca , Ca +, Mg and K , among others. Not finding absorption for any of the investigated species, we are able to set absorption limits with a median value of 1.9 × RP. In conclusion, we do not find evidence of a widely extended silicate envelope on this superEarth reaching several planetary radii.

2D maps of the residual spectra at different orbital phases in the velocity range for strong opacity bearing species i.e. Mg I (top), H beta, and K I (center) and Ca II (bottom). The color bar shows the residual Flux in %. The dashed black line shows the expected absorption trace.

Read more: Keles et al. 2022, MNRAS, 513, 1544

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