scholarly journals Sectoral r modes and periodic radial velocity variations of Sun-like stars

2019 ◽  
Vol 623 ◽  
pp. A50 ◽  
Author(s):  
A. F. Lanza ◽  
L. Gizon ◽  
T. V. Zaqarashvili ◽  
Z.-C. Liang ◽  
K. Rodenbeck
Keyword(s):  
Radial Velocity ◽  
Rotation Axis ◽  
Rotation Period ◽  
Maximum Amplitude ◽  
Global Scale ◽  
Surface Velocity ◽  
The Sun ◽  
Stellar Rotation ◽  
Restoring Force ◽  
Transiting Planets

Context. Radial velocity (RV) measurements are used to search for planets orbiting late-type main-sequence stars and to confirm the transiting planets. Aims. The most advanced spectrometers are now approaching a precision of ~10 cm s−1, which implies the need to identify and correct for all possible sources of RV oscillations intrinsic to the star down to this level and possibly beyond. The recent discovery of global-scale equatorial Rossby waves in the Sun, also called r modes, prompted us to investigate their possible signature in stellar RV measurements. These r modes are toroidal modes of oscillation whose restoring force is the Coriolis force; they propagate in the retrograde direction in a frame that co-rotates with the star. The solar r modes with azimuthal orders 3 ≤ m ≲ 15 were identified unambiguously because of their dispersion relation and their long e-folding lifetimes of hundreds of days. Methods. In this paper, we simulate the RV oscillations produced by sectoral r modes with 2 ≤ m ≤ 5 by assuming a stellar rotation period of 25.54 days and a maximum amplitude of the surface velocity of each mode of 2 m s−1. This amplitude is representative of the solar measurements except for the m = 2 mode, which has not yet been observed on the Sun. Results. Sectoral r modes with azimuthal orders m = 2 and 3 would produce RV oscillations with amplitudes of 76.4 and 19.6 cm s−1 and periods of 19.16 and 10.22 days, respectively, for a star with an inclination of the rotation axis to the line of sight i = 60°. Therefore, they may produce rather sharp peaks in the Fourier spectrum of the radial velocity time series that could lead to spurious planetary detections. Conclusions. Sectoral r modes may represent a source of confusion in the case of slowly rotating inactive stars that are preferential targets for RV planet search. The main limitation of the present investigation is the lack of observational constraints on the amplitude of the m = 2 mode on the Sun.

scholarly journals WASP-166b: a bloated super-Neptune transiting a V  = 9 star

2019 ◽  
Vol 488 (3) ◽  
pp. 3067-3075 ◽  
Author(s):  
Coel Hellier ◽  
D R Anderson ◽  
A H M J Triaud ◽  
F Bouchy ◽  
A Burdanov ◽  
...  
Keyword(s):  
Radial Velocity ◽  
Rotation Axis ◽  
Rotation Period ◽  
Magnetic Activity ◽  
Stellar Rotation ◽  
Velocity Measurements

Abstract We report the discovery of WASP-166b, a super-Neptune planet with a mass of 0.1 MJup (1.9 MNep) and a bloated radius of 0.63 RJup. It transits a V = 9.36, F9V star in a 5.44-d orbit that is aligned with the stellar rotation axis (sky-projected obliquity angle λ = 3 ± 5 deg). Variations in the radial-velocity measurements are likely the result of magnetic activity over a 12-d stellar rotation period. WASP-166b appears to be a rare object within the ‘Neptune desert’.

scholarly journals Misaligned spin-orbit in the XO-3 planetary system?

2008 ◽  
Vol 4 (S253) ◽  
pp. 508-511
Author(s):  
G. Hébrard ◽  
F. Bouchy ◽  
F. Pont ◽  
B. Loeillet ◽  
M. Rabus ◽  
...  
Keyword(s):  
Radial Velocity ◽  
Planetary System ◽  
Rotation Axis ◽  
Gravitational Interaction ◽  
Stellar Rotation ◽  
Velocity Anomaly ◽  
Large Program ◽  
Formation And Evolution ◽  
Unusual Shape ◽  
Orbital Axis

AbstractThe SOPHIE Consortium started a large program of exoplanets search and characterization in the Northern hemisphere with the new spectrograph SOPHIE at the 1.93-m telescope of Haute-Provence Observatory, France. The objectives of this program are to characterize the zoo of exoplanets and to bring strong constraints on their processes of formation and evolution using the radial velocity technique. We present here new SOPHIE measurements of the transiting planet host star XO-3. This allowed us to observe the Rossiter-McLaughlin effect and to refine the parameters of the planet. The unusual shape of the radial velocity anomaly during the transit provides a hint for a nearly transverse Rossiter-McLaughlin effect. The sky-projected angle between the planetary orbital axis and the stellar rotation axis should be λ = 70° ± 15° to be compatible with our observations. This suggests that some close-in planets might result from gravitational interaction between planets and/or stars rather than migration. This result requires confirmation by additional observations.

scholarly journals Connecting measurements of solar and stellar brightness variations

2020 ◽  
Vol 638 ◽  
pp. A56
Author(s):  
N.-E. Nèmec ◽  
E. Işık ◽  
A. I. Shapiro ◽  
S. K. Solanki ◽  
N. A. Krivova ◽  
...  
Keyword(s):  
Transport Model ◽  
Rotation Axis ◽  
Surface Flux ◽  
Light Curves ◽  
The Sun ◽  
Solar Cycles ◽  
Stellar Rotation ◽  
Flux Transport ◽  
Surface Distribution ◽  
The Difference

Context. A comparison of solar and stellar brightness variations is hampered by the difference in spectral passbands that are used in observations, and also by the possible difference in the inclination of the solar and stellar rotation axes from the line of sight. Aims. We calculate the rotational variability of the Sun as it would be measured in passbands used for stellar observations. In particular, we consider the filter systems used by the CoRoT, Kepler, TESS, and Gaia space missions. We also quantify the effect of the inclination of the rotation axis on the solar rotational variability. Methods. We employed the spectral and total irradiance reconstruction (SATIRE) model to calculate solar brightness variations in different filter systems as observed from the ecliptic plane. We then combined the simulations of the surface distribution of the magnetic features at different inclinations using a surface flux transport model with the SATIRE calculations to compute the dependence of the variability on the inclination. Results. For an ecliptic-bound observer, the amplitude of the solar rotational variability, as observed in the total solar irradiance (TSI), is 0.68 mmag (averaged over solar cycles 21–24). We obtained corresponding amplitudes in the Kepler (0.74 mmag), CoRoT (0.73 mmag), TESS (0.62 mmag), Gaia G (0.74 mmag), Gaia GRP (0.62 mmag), and Gaia GBP (0.86 mmag) passbands. Decreasing the inclination of the rotation axis decreases the rotational variability. For a sample of randomly inclined stars, the variability is on average 15% lower in all filter systems we considered. This almost compensates for the difference in amplitudes of the variability in TSI and Kepler passbands, making the amplitudes derived from the TSI records an ideal representation of the solar rotational variability for comparison to Kepler stars with unknown inclinations. Conclusions. The TSI appears to be a relatively good measure of solar variability for comparisons with stellar measurements in the CoRoT, Kepler, TESS Gaia G, and Gaia GRP filters. Whereas the correction factors can be used to convert the variability amplitude from solar measurements into the values expected for stellar missions, the inclination affects the shapes of the light curves so that a much more sophisticated correction than simple scaling is needed to obtain light curves out of the ecliptic for the Sun.

scholarly journals Spin-orbit alignment and magnetic activity in the young planetary system AU Mic

2020 ◽  
Vol 641 ◽  
pp. L1 ◽  
Author(s):  
E. Martioli ◽  
G. Hébrard ◽  
C. Moutou ◽  
J.-F. Donati ◽  
É. Artigau ◽  
...  
Keyword(s):  
Radial Velocity ◽  
Template Matching ◽  
Near Infrared ◽  
Rotation Axis ◽  
Magnetic Activity ◽  
Radial Velocities ◽  
Model Parameters ◽  
Correlation Technique ◽  
Spin Orbit ◽  
Stellar Rotation

We present high-resolution near-infrared spectropolarimetric observations using the SPIRou instrument at Canada-France-Hawaii Telescope (CFHT) during a transit of the recently detected young planet AU Mic b, with supporting spectroscopic data from iSHELL at NASA InfraRed Telescope Facility. We detect Zeeman signatures in the Stokes V profiles and measure a mean longitudinal magnetic field of ¯Bℓ = 46.3 ± 0.7 G. Rotationally modulated magnetic spots likely cause long-term variations of the field with a slope of dBℓ/dt = −108.7 ± 7.7 G d−1. We apply the cross-correlation technique to measure line profiles and obtain radial velocities through CCF template matching. We find an empirical linear relationship between radial velocity and Bℓ, which allows us to estimate the radial-velocity induced by stellar activity through rotational modulation of spots for the five hours of continuous monitoring of AU Mic with SPIRou. We model the corrected radial velocities for the classical Rossiter-McLaughlin effect, using MCMC to sample the posterior distribution of the model parameters. This analysis shows that the orbit of AU Mic b is prograde and aligned with the stellar rotation axis with a sky-projected spin-orbit obliquity of λ = 0°−15°+18°. The aligned orbit of AU Mic b indicates that it formed in the protoplanetary disk that evolved into the current debris disk around AU Mic.

scholarly journals The Sun Through Time

2020 ◽  
Vol 216 (8) ◽  
Author(s):  
Manuel Güdel
Keyword(s):  
Stellar Wind ◽  
Rotation Period ◽  
High Energy ◽  
Magnetic Activity ◽  
Energy Output ◽  
The Sun ◽  
Stellar Rotation ◽  
Solar Mass ◽  
Rotation Periods ◽  
Rotational Evolution

AbstractMagnetic activity of stars like the Sun evolves in time because of spin-down owing to angular momentum removal by a magnetized stellar wind. These magnetic fields are generated by an internal dynamo driven by convection and differential rotation. Spin-down therefore converges at an age of about 700 Myr for solar-mass stars to values uniquely determined by the stellar mass and age. Before that time, however, rotation periods and their evolution depend on the initial rotation period of a star after it has lost its protostellar/protoplanetary disk. This non-unique rotational evolution implies similar non-unique evolutions for stellar winds and for the stellar high-energy output. I present a summary of evolutionary trends for stellar rotation, stellar wind mass loss and stellar high-energy output based on observations and models.

scholarly journals Decoding the radial velocity variations of HD 41248 with ESPRESSO

2020 ◽  
Vol 635 ◽  
pp. A13 ◽  
Author(s):  
J. P. Faria ◽  
V. Adibekyan ◽  
E. M. Amazo-Gómez ◽  
S. C. C. Barros ◽  
J. D. Camacho ◽  
...  
Keyword(s):  
Light Curve ◽  
Radial Velocity ◽  
Gaussian Process ◽  
Process Model ◽  
Moving Average ◽  
Rotation Period ◽  
Magnetic Activity ◽  
Noise Model ◽  
Stellar Rotation ◽  
Gaussian Process Model

Context. Twenty-four years after the discoveries of the first exoplanets, the radial-velocity (RV) method is still one of the most productive techniques to detect and confirm exoplanets. But stellar magnetic activity can induce RV variations large enough to make it difficult to disentangle planet signals from the stellar noise. In this context, HD 41248 is an interesting planet-host candidate, with RV observations plagued by activity-induced signals. Aims. We report on ESPRESSO observations of HD 41248 and analyse them together with previous observations from HARPS with the goal of evaluating the presence of orbiting planets. Methods. Using different noise models within a general Bayesian framework designed for planet detection in RV data, we test the significance of the various signals present in the HD 41248 dataset. We use Gaussian processes as well as a first-order moving average component to try to correct for activity-induced signals. At the same time, we analyse photometry from the TESS mission, searching for transits and rotational modulation in the light curve. Results. The number of significantly detected Keplerian signals depends on the noise model employed, which can range from 0 with the Gaussian process model to 3 with a white noise model. We find that the Gaussian process alone can explain the RV data while allowing for the stellar rotation period and active region evolution timescale to be constrained. The rotation period estimated from the RVs agrees with the value determined from the TESS light curve. Conclusions. Based on the data that is currently available, we conclude that the RV variations of HD 41248 can be explained by stellar activity (using the Gaussian process model) in line with the evidence from activity indicators and the TESS photometry.

scholarly journals Monitoring of the activity and composition of comets 41P/Tuttle–Giacobini–Kresak and 45P/Honda–Mrkos–Pajdusakova

2018 ◽  
Vol 619 ◽  
pp. A156 ◽  
Author(s):  
Y. Moulane ◽  
E. Jehin ◽  
C. Opitom ◽  
F. J. Pozuelos ◽  
J. Manfroid ◽  
...  
Keyword(s):  
Production Rate ◽  
Rotation Period ◽  
The Sun ◽  
Water Production ◽  
Production Rates ◽  
Transiting Planets ◽  
Small Telescope ◽  
Typical Composition ◽  
Water Production Rate ◽  
Daughter Species

We report on photometry and imaging of the Jupiter family comets 41P/Tuttle–Giacobini–Kresak and 45P/Honda–Mrkos–Pajdusakova with the TRAPPIST-North (TRAnsiting Planets and PlanetesImals Small Telescope) telescope. We observed 41P on 34 nights from February 16 to July 27, 2017, pre- and post-perihelion (rh = 1.04 au), and collected data for comet 45P after perihelion (rh = 0.53 au) from February 10 to March 30, 2017. We computed the production rates of the daughter species OH, NH, CN, C3 and C2 and we measured the dust proxy, Afρ, for both comets. The peak of water-production rate of 41P was (3.46 ± 0.20) × 1027 molecules s−1 on April 3, 2017, when the comet was at 1.05 au from the Sun. We have shown that the activity of 41P is decreasing by about 30–40% from one apparition to the next. We measured a mean water-production rate for 45P of (1.43 ± 0.62) × 1027 molecules s−1 during a month after perihelion. Our results show that these Jupiter family comets had low gas and dust activity and no outburst was detected. Relative abundances, expressed as ratios of production rates and the Afρ parameter with respect to OH and to CN, were compared to those measured in other comets. We found that 41P and 45P have a typical composition in terms of carbon-bearing species. The study of coma features exhibited by the CN gas species allowed the measurement of the rotation period of 41P, showing a surprisingly large increase of the rotation period from (30 ± 5) h at the end of March to (50 ± 10) h at the end of April, 2017, in agreement with recent observations by other teams.

scholarly journals Eyes on K2-3: A system of three likely sub-Neptunes characterized with HARPS-N and HARPS

2018 ◽  
Vol 615 ◽  
pp. A69 ◽  
Author(s):  
M. Damasso ◽  
A. S. Bonomo ◽  
N. Astudillo-Defru ◽  
X. Bonfils ◽  
L. Malavolta ◽  
...  
Keyword(s):  
Time Series ◽  
Radial Velocity ◽  
Rotation Period ◽  
Doppler Signal ◽  
Stellar Rotation ◽  
Mass Measurements ◽  
Stellar Activity ◽  
Velocity Signal ◽  
M Dwarf ◽  
High Cadence

Context. M-dwarf stars are promising targets for identifying and characterizing potentially habitable planets. K2-3 is a nearby (45 pc), early-type M dwarf hosting three small transiting planets, the outermost of which orbits close to the inner edge of the stellar (optimistic) habitable zone. The K2-3 system is well suited for follow-up characterization studies aimed at determining accurate masses and bulk densities of the three planets. Aims. Using a total of 329 radial velocity measurements collected over 2.5 years with the HARPS-N and HARPS spectrographs and a proper treatment of the stellar activity signal, we aim to improve measurements of the masses and bulk densities of the K2-3 planets. We use our results to investigate the physical structure of the planets. Methods. We analysed radial velocity time series extracted with two independent pipelines using Gaussian process regression. We adopted a quasi-periodic kernel to model the stellar magnetic activity jointly with the planetary signals. We used Monte Carlo simulations to investigate the robustness of our mass measurements of K2-3 c and K2-3 d, and to explore how additional high-cadence radial velocity observations might improve these values. Results. Even though the stellar activity component is the strongest signal present in the radial velocity time series, we are able to derive masses for both planet b (Mb = 6.6 ± 1.1 M⊕) and planet c (Mc = 3.1−1.2+1.3 M⊕). The Doppler signal from K2-3 d remains undetected, likely because of its low amplitude compared to the radial velocity signal induced by the stellar activity. The closeness of the orbital period of K2-3 d to the stellar rotation period could also make the detection of the planetary signal complicated. Based on our ability to recover injected signals in simulated data, we tentatively estimate the mass of K2-3 d to be Md = 2.7−0.8+1.2 M⊕ M⊕. These mass measurements imply that the bulk densities and therefore the interior structures of the three planets may be similar. In particular, the planets may either have small H/He envelopes (<1%) or massive water layers, with a water content ≥50% of their total mass, on top of rocky cores. Placing further constraints on the bulk densities of K2-3 c and d is difficult; in particular, we would not have been able to detect the Doppler signal of K2-3 d even by adopting a semester of intense, high-cadence radial velocity observations with HARPS-N and HARPS.

scholarly journals HADES RV programme with HARPS-N at TNG

2018 ◽  
Vol 612 ◽  
pp. A89 ◽  
Author(s):  
A. Suárez Mascareño ◽  
R. Rebolo ◽  
J. I. González Hernández ◽  
B. Toledo-Padrón ◽  
M. Perger ◽  
...  
Keyword(s):  
Radial Velocity ◽  
Rotation Period ◽  
Stellar Rotation ◽  
M Dwarfs ◽  
Velocity Signal ◽  
The Public ◽  
Rotation Periods ◽  
Chromospheric Emission ◽  
The Mean ◽  
Magnetic Cycles

We aim to investigate the presence of signatures of magnetic cycles and rotation on a sample of 71 early M-dwarfs from the HADES RV programme using high-resolution time-series spectroscopy of the Ca II H&K and Hα chromospheric activity indicators, the radial velocity series, the parameters of the cross correlation function and the V -band photometry. We used mainly HARPS-N spectra, acquired over 4 yr, and add HARPS spectra from the public ESO database and ASAS photometry light-curves as support data, extending the baseline of the observations of some stars up to 12 yr. We provide log10(R′HK) measurements for all the stars in the sample, cycle length measurements for 13 stars, rotation periods for 33 stars and we are able to measure the semi-amplitude of the radial velocity signal induced by rotation in 16 stars. We complement our work with previous results and confirm and refine the previously reported relationships between the mean level of chromospheric emission, measured by the log10(R′HK), with the rotation period, and with the measured semi-amplitude of the activity induced radial velocity signal for early M-dwarfs. We searched for a possible relation between the measured rotation periods and the lengths of the magnetic cycle, finding a weak correlation between both quantities. Using previous v sin i measurements we estimated the inclinations of the star’s poles to the line of sight for all the stars in the sample, and estimate the range of masses of the planets GJ 3998 b and c (2.5–4.9 and 6.3–12.5 M⊕), GJ 625 b (2.82 M⊕), GJ 3942 b (7.1–10.0 M⊕) and GJ 15A b (3.1–3.3 M⊕), assuming their orbits are coplanar with the stellar rotation.

scholarly journals The SOPHIE search for northern extrasolar planets

2020 ◽  
Vol 636 ◽  
pp. L6 ◽  
Author(s):  
N. C. Hara ◽  
F. Bouchy ◽  
M. Stalport ◽  
I. Boisse ◽  
J. Rodrigues ◽  
...  
Keyword(s):  
Radial Velocity ◽  
Extrasolar Planets ◽  
Statistical Significance ◽  
Rotation Period ◽  
Low Frequency ◽  
Stellar Rotation ◽  
Strong Candidate ◽  
A New Technique ◽  
Photometric Measurements ◽  
Three Body

Aims. Since 2011, the SOPHIE spectrograph has been used to search for Neptunes and super-Earths in the northern hemisphere. As part of this observational program, 290 radial velocity measurements of the 6.4 V magnitude star HD 158259 were obtained. Additionally, TESS photometric measurements of this target are available. We present an analysis of the SOPHIE data and compare our results with the output of the TESS pipeline. Methods. The radial velocity data, ancillary spectroscopic indices, and ground-based photometric measurements were analyzed with classical and ℓ1 periodograms. The stellar activity was modeled as a correlated Gaussian noise and its impact on the planet detection was measured with a new technique. Results. The SOPHIE data support the detection of five planets, each with m sin i ≈ 6 M⊕, orbiting HD 158259 in 3.4, 5.2, 7.9, 12, and 17.4 days. Though a planetary origin is strongly favored, the 17.4 d signal is classified as a planet candidate due to a slightly lower statistical significance and to its proximity to the expected stellar rotation period. The data also present low frequency variations, most likely originating from a magnetic cycle and instrument systematics. Furthermore, the TESS pipeline reports a significant signal at 2.17 days corresponding to a planet of radius ≈1.2 R⊕. A compatible signal is seen in the radial velocities, which confirms the detection of an additional planet and yields a ≈2 M⊕ mass estimate. Conclusions. We find a system of five planets and a strong candidate near a 3:2 mean motion resonance chain orbiting HD 158259. The planets are found to be outside of the two and three body resonances.

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