16 research outputs found
Orbital misalignment of the super-Earth Men c with the spin of its star
Planet-planet scattering events can leave an observable trace of a planet's
migration history in the form of orbital misalignment with respect to the the
stellar spin axis, which is measurable from spectroscopic timeseries taken
during transit. We present high-resolution spectroscopic transits observed with
ESPRESSO of the close-in super-Earth Men c. The system also contains an
outer giant planet on a wide, eccentric orbit, recently found to be inclined
with respect to the inner planetary orbit. These characteristics are
reminiscent of past dynamical interactions. We successfully retrieve the
planet-occulted light during transit and find evidence that the orbit of
Men c is moderately misaligned with the stellar spin axis with ().
This is consistent with the super-Earth Men c having followed a
high-eccentricity migration followed by tidal circularisation, and hints that
super-Earths can form at large distances from their star. We also detect clear
signatures of solar-like oscillations within our ESPRESSO radial velocity
timeseries, where we reach a radial velocity precision of cm/s. We
model the oscillations using Gaussian processes and retrieve a frequency of
maximum oscillation, Hz. These
oscillations makes it challenging to detect the Rossiter-McLaughlin effect
using traditional methods. We are, however, successful using the reloaded
Rossiter-McLaughlin approach. Finally, in an appendix we also present updated
physical parameters and ephemerides for Men c from a Gaussian process
transit analysis of the full TESS Cycle 1 data.Comment: 20 pages, 11 figures. Published in MNRA
The EBLM project. VII. Spin-orbit alignment for the circumbinary planet host EBLM J0608-59 A/TOI-1338 A
Funding: This work was inpart funded by the U.S.âNorway Fulbright Foundation and a NASATESSGI grant G022253 (PI: Martin). AHMJT received funding from the European Research Council (ERC) under the European Unionâs Horizon 2020 research and innovation programme (grant 803193/BEBOP), and from a Leverhulme Trust Research Project grant (RPG-2018-418). VKH is also supported by a Birmingham Doctoral Scholarship, and by a studentship from Birminghamâs School of Physics & Astronomy. DVM received funding from the Swiss National Science Foundation (grant P 400P2 186735). SG has been supported by STFC through consolidated grants ST/L000733/1and ST/P000495/1.A dozen short-period detached binaries are known to host transiting circumbinary planets. In all circumbinary systems so far, the planetary and binary orbits are aligned within a couple of degrees. However, the obliquity of the primary star, which is an important tracer of their formation, evolution, and tidal history, has only been measured in one circumbinary system until now. EBLM J0608-59/TOI-1338 is a low-mass eclipsing binary system with a recently discovered circumbinary planet identified by TESS. Here, we perform high-resolution spectroscopy during primary eclipse to measure the projected stellar obliquity of the primary component. The obliquity is low, and thus the primary star is aligned with the binary and planetary orbits with a projected spin-orbit angle ÎČ = 2.°8 ± 17.°1. The rotation period of18.1 ± 1.6 d implied by our measurement of vsinIâ suggests that the primary has not yet pseudo-synchronized with the binary orbit, but is consistent with gyrochronology and weak tidal interaction with the binary companion. Our result, combined with the known coplanarity of the binary and planet orbits, is suggestive of formation from a single disc. Finally, we considered whether the spectrum of the faint secondary star could affect our measurements. We show through simulations that the effect is negligible for our system, but can lead to strong biases in vsinIâ and ÎČ for higher flux ratios. We encourage future studies in eclipse spectroscopy test the assumption of a dark secondary for flux ratios âł1ppt.Publisher PDFPeer reviewe
The EXPRES Stellar Signals Project II. State of the Field in Disentangling Photospheric Velocities
Measured spectral shifts due to intrinsic stellar variability (e.g., pulsations, granulation) and activity (e.g., spots, plages) are the largest source of error for extreme-precision radial-velocity (EPRV) exoplanet detection. Several methods are designed to disentangle stellar signals from true center-of-mass shifts due to planets. The Extreme-precision Spectrograph (EXPRES) Stellar Signals Project (ESSP) presents a self-consistent comparison of 22 different methods tested on the same extreme-precision spectroscopic data from EXPRES. Methods derived new activity indicators, constructed models for mapping an indicator to the needed radial-velocity (RV) correction, or separated out shape- and shift-driven RV components. Since no ground truth is known when using real data, relative method performance is assessed using the total and nightly scatter of returned RVs and agreement between the results of different methods. Nearly all submitted methods return a lower RV rms than classic linear decorrelation, but no method is yet consistently reducing the RV rms to sub-meter-per-second levels. There is a concerning lack of agreement between the RVs returned by different methods. These results suggest that continued progress in this field necessitates increased interpretability of methods, high-cadence data to capture stellar signals at all timescales, and continued tests like the ESSP using consistent data sets with more advanced metrics for method performance. Future comparisons should make use of various well-characterized data setsâsuch as solar data or data with known injected planetary and/or stellar signalsâto better understand method performance and whether planetary signals are preserved
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The effect of stellar contamination on low-resolution transmission spectroscopy: needs identified by NASAâs Exoplanet Exploration Program Study Analysis Group 21
Study Analysis Group 21 (SAG21) of NASAâs Exoplanet Exploration Program Analysis Group was organized to study the effect of stellar contamination on space-based transmission spectroscopy, a method for studying exoplanetary atmospheres by measuring the wavelength-dependent radius of a planet as it transits its star. Transmission spectroscopy relies on a precise understanding of the spectrum of the star being occulted. However, stars are not homogeneous, constant light sources but have temporally evolving photospheres and chromospheres with inhomogeneities like spots, faculae, plages, granules, and flares. This SAG brought together an interdisciplinary team of more than 100 scientists, with observers and theorists from the heliophysics, stellar astrophysics, planetary science, and exoplanetary atmosphere research communities, to study the current research needs that can be addressed in this context to make the most of transit studies from current NASA facilities like Hubble Space Telescope and JWST. The analysis produced 14 findings, which fall into three science themes encompassing (i) how the Sun is used as our best laboratory to calibrate our understanding of stellar heterogeneities (âThe Sun as the Stellar Benchmarkâ), (ii) how stars other than the Sun extend our knowledge of heterogeneities (âSurface Heterogeneities of Other Starsâ), and (iii) how to incorporate information gathered for the Sun and other stars into transit studies (âMapping Stellar Knowledge to Transit Studiesâ). In this invited review, we largely reproduce the final report of SAG21 as a contribution to the peer-reviewed literature
Filtering solar-like oscillations for exoplanet detection in radial velocity observations
Cool main-sequence, sub-giant and red-giant stars all show solar-like
oscillations, pulsations that are excited and intrinsically damped by
near-surface convection. Many overtones are typically excited to observable
amplitudes, giving a rich spectrum of detectable modes. These modes provide a
wealth of information on fundamental stellar properties. However, the radial
velocity shifts induced by these oscillations can also be problematic when
searching for low-mass, long-period planets; this is because their amplitudes
are large enough to completely mask such minute planetary signals. Here we show
how fine-tuning exposure times to the stellar parameters can help efficiently
average out the solar-like-oscillation-induced shifts. To reduce the
oscillation signal to the radial velocity precision commensurate with an
Earth-analogue, we find that for cool, low-mass stars (near spectral type K)
the necessary exposure times may be as short as 4 minutes, while for hotter,
higher-mass stars (near spectral type F, or slightly evolved) the required
exposure times can be longer than 100 minutes. We provide guideline exposure
durations required to suppress the total observed amplitude due to oscillations
to a level of , and a level corresponding to the
Earth-analogue reflex amplitude for the star. Owing to the intrinsic stochastic
variability of the oscillations, we recommend in practice choosing short
exposure durations at the telescope and then averaging over those exposures
later, as guided by our predictions. To summarize, as we enter an era of
instrumental precision, it is critical to tailor our
observing strategies to the stellar properties.Comment: 22 pages, 6 figures; accepted for publication in Astronomical Journal
(AAS Journals
Atmospheric composition of WASP-85Ab with ESPRESSO/VLT observations
Transit spectroscopy is the most frequently used technique to reveal the atmospheric properties of exoplanets. At high resolution, it has the added advantage of resolving the small Doppler shift of spectral lines and, thus, the trace signal of the exoplanet atmosphere can be extracted separately. We obtained the transmission spectra of the extrasolar planet WASP-85Ab, a hot Jupiter in a 2.655-day orbit around a G5, V = 11.2 mag host star, observed by the high-resolution spectrograph ESPRESSO at the Very Large Telescope array for three transits. We present an analysis of the Rossiter-McLaughlin (RM) effect on WASP-85A and determine a spin-orbit angle λ = â16.155°â2.879+2.916, suggesting that the planet is in a nearly aligned orbit. Combining the transmission spectra of three nights, we tentatively detected Hα and Call absorption with âȘ3Ï via direct visual inspection of the transmission spectra with the center-to-limb variation and the Rossiter-McLaughlin effects removed; these absorptions still remain visible after excluding the cores of these strong lines with a 0.1Ă
mask. These spectral signals appear likely to have originated from the planetary atmosphere, but we cannot fully exclude a stellar origin. Via the cross-correlation analysis of a set of atoms and molecules, LiâŻ
High-resolution transmission spectroscopy of MASCARA-2 b with EXPRES
We report detections of atomic species in the atmosphere of MASCARA-2 b, using the first transit observations obtained with the newly commissioned EXPRES spectrograph. EXPRES is a highly stabilized optical echelle spectrograph, designed to detect stellar reflex motions with amplitudes down to 30 cm sâ1, and has recently been deployed at the Lowell Discovery Telescope. By analyzing the transmission spectrum of the ultra-hot Jupiter MASCARA-2 b using the cross-correlation method, we confirm previous detections of FeâŻI, FeâŻII, and NaâŻI, which likely originate in the upper regions of the inflated atmosphere. In addition, we report significant detections of MgâŻI and CrâŻII. The absorption strengths change slightly with time, possibly indicating different temperatures and chemistry in the day- and nightside terminators. Using the effective stellar line-shape variation induced by the transiting planet, we constrain the projected spin-orbit misalignment of the system to 1.6 ± 3.1 degrees, consistent with an aligned orbit. We demonstrate that EXPRES joins a suite of instruments capable of phase-resolved spectroscopy of exoplanet atmospheres
The EBLM project. VII. Spin-orbit alignment for the circumbinary planet host EBLM J0608-59 A/TOI-1338 A
A dozen short-period detached binaries are known to host transiting circumbinary planets. In all circumbinary systems so far, the planetary and binary orbits are aligned within a couple of degrees. However, the obliquity of the primary star, which is an important tracer of their formation, evolution, and tidal history, has only been measured in one circumbinary system until now. EBLM J0608-59/TOI-1338 is a low-mass eclipsing binary system with a recently discovered circumbinary planet identified by TESS. Here, we perform high-resolution spectroscopy during primary eclipse to measure the projected stellar obliquity of the primary component. The obliquity is low, and thus the primary star is aligned with the binary and planetary orbits with a projected spin-orbit angle ÎČ = 2.°8 ± 17.°1. The rotation period of18.1 ± 1.6 d implied by our measurement of vsinIâ suggests that the primary has not yet pseudo-synchronized with the binary orbit, but is consistent with gyrochronology and weak tidal interaction with the binary companion. Our result, combined with the known coplanarity of the binary and planet orbits, is suggestive of formation from a single disc. Finally, we considered whether the spectrum of the faint secondary star could affect our measurements. We show through simulations that the effect is negligible for our system, but can lead to strong biases in vsinIâ and ÎČ for higher flux ratios. We encourage future studies in eclipse spectroscopy test the assumption of a dark secondary for flux ratios âł1ppt
Connecting photometric and spectroscopic granulation signals with CHEOPS and ESPRESSO
Context. Stellar granulation generates fluctuations in photometric and spectroscopic data whose properties depend on the stellar type, composition, and evolutionary state. Characterizing granulation is key for understanding stellar atmospheres and detecting planets. Aims. We aim to detect the signatures of stellar granulation, link spectroscopic and photometric signatures of convection for mainsequence stars, and test predictions from 3D hydrodynamic models. Methods. For the first time, we observed two bright stars (Teff = 5833 and 6205 K) with high-precision observations taken simultaneously with CHEOPS and ESPRESSO. We analyzed the properties of the stellar granulation signal in each individual dataset. We compared them to Kepler observations and 3D hydrodynamic models. While isolating the granulation-induced changes by attenuating and filtering the p-mode oscillation signals, we studied the relationship between photometric and spectroscopic observables. Results. The signature of stellar granulation is detected and precisely characterized for the hotter F star in the CHEOPS and ESPRESSO observations. For the cooler G star, we obtain a clear detection in the CHEOPS dataset only. The TESS observations are blind to this stellar signal. Based on CHEOPS observations, we show that the inferred properties of stellar granulation are in agreement with both Kepler observations and hydrodynamic models. Comparing their periodograms, we observe a strong link between spectroscopic and photometric observables. Correlations of this stellar signal in the time domain (flux versus radial velocities, RV) and with specific spectroscopic observables (shape of the cross-correlation functions) are however difficult to isolate due to S/N dependent variations. Conclusions. In the context of the upcoming PLATO mission and the extreme precision RV surveys, a thorough understanding of the properties of the stellar granulation signal is needed. The CHEOPS and ESPRESSO observations pave the way for detailed analyses of this stellar process.ISSN:0004-6361ISSN:1432-074