scholarly journals A hot mini-Neptune in the radius valley orbiting solar analogue HD 110113

2021 ◽  
Author(s):  
H P Osborn ◽  
D J Armstrong ◽  
V Adibekyan ◽  
K A Collins ◽  
E Delgado-Mena ◽  
...  
Keyword(s):  
Gaussian Process ◽  
Radial Velocities ◽  
Stellar Rotation ◽  
Incident Flux ◽  
Rotation Signal

Abstract We report the discovery of HD 110113 b (TOI-755.01), a transiting mini-Neptune exoplanet on a 2.5-day orbit around the solar-analogue HD 110113 (Teff= 5730K). Using TESS photometry and HARPS radial velocities gathered by the NCORES program, we find HD 110113 b has a radius of 2.05 ± 0.12  R⊕ and a mass of 4.55 ± 0.62  M⊕. The resulting density of $2.90^{+0.75}_{-0.59}$  g cm−3 is significantly lower than would be expected from a pure-rock world; therefore, HD 110113 b must be a mini-Neptune with a significant volatile atmosphere. The high incident flux places it within the so-called radius valley; however, HD 110113 b was able to hold on to a substantial (0.1-1 per cent) H-He atmosphere over its ∼4Gyr lifetime. Through a novel simultaneous Gaussian process fit to multiple activity indicators, we were also able to fit for the strong stellar rotation signal with period 20.8 ± 1.2  d from the RVs and confirm an additional non-transiting planet, HD 110113 c, which has a mass of 10.5 ± 1.2  M⊕ and a period of $6.744^{+0.008}_{-0.009}$  d.

scholarly journals Exploring the robustness of Keplerian signals to the removal of active and telluric features

2020 ◽  
Vol 500 (1) ◽  
pp. 548-557
Author(s):  
M Lisogorskyi ◽  
H R A Jones ◽  
F Feng ◽  
R P Butler ◽  
S Vogt
Keyword(s):  
Monte Carlo ◽  
High Resolution ◽  
Monte Carlo Simulations ◽  
Large Amplitude ◽  
Absorption Cell ◽  
Stellar Rotation ◽  
Long Period ◽  
Active Line ◽  
Low Amplitude ◽  
Rotation Signal

ABSTRACT We examine the influence of activity- and telluric-induced radial velocity (RV) signals on high-resolution spectra taken with an iodine absorption cell. We exclude 2-$\mathring{\rm A}$ spectral chunks containing active and telluric lines based on the well-characterized K1V star α Centauri B and illustrate the method on Epsilon Eridani – an active K2V star with a long-period, low-amplitude planetary signal. After removal of the activity- and telluric-sensitive parts of the spectrum from the RV calculation, the significance of the planetary signal is increased and the stellar rotation signal disappears. In order to assess the robustness of the procedure, we perform Monte Carlo simulations based on removing random chunks of the spectrum. Simulations confirm that the removal of lines impacted by activity and tellurics provides a method for checking the robustness of a given Keplerian signal. We also test the approach on HD 40979, which is an active F8V star with a large-amplitude planetary signal. Our Monte Carlo simulations reveal that the significance of the Keplerian signal in the F star is much more sensitive to wavelength. Unlike the K star, the removal of active lines from the F star greatly reduces the RV precision. In this case, our removal of a K star active line from an F star does not a provide a simple useful diagnostic because it has far less RV information and heavily relies on the strong active lines.

scholarly journals Stellar Rotation and Precise Radial Velocities

1999 ◽  
Vol 170 ◽  
pp. 243-254 ◽  
Author(s):  
David F. Gray
Keyword(s):  
Radial Velocities ◽  
Spectral Lines ◽  
Stellar Rotation ◽  
Rotation Rates

AbstractThis paper focuses on the limitations of establishing rotation rates (to be thought of as differential radial velocities across the surface of the star) and how rotation infringes on our ability to measure precise positions of spectral lines and hence spectroscopic radial velocities.

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 Distinguishing the albedo of exoplanets from stellar activity

2018 ◽  
Vol 611 ◽  
pp. A8 ◽  
Author(s):  
L. M. Serrano ◽  
S. C. C. Barros ◽  
M. Oshagh ◽  
N. C. Santos ◽  
J. P. Faria ◽  
...  
Keyword(s):  
Gaussian Process ◽  
Noise Level ◽  
Light Curves ◽  
Phase Curve ◽  
Stellar Rotation ◽  
Stellar Activity ◽  
Light Component ◽  
Instrumental Noise ◽  
Reflected Light ◽  
Planetary Albedo

Context. Light curves show the flux variation from the target star and its orbiting planets as a function of time. In addition to the transit features created by the planets, the flux also includes the reflected light component of each planet, which depends on the planetary albedo. This signal is typically referred to as phase curve and could be easily identified if there were no additional noise. As well as instrumental noise, stellar activity, such as spots, can create a modulation in the data, which may be very difficult to distinguish from the planetary signal. Aims. We analyze the limitations imposed by the stellar activity on the detection of the planetary albedo, considering the limitations imposed by the predicted level of instrumental noise and the short duration of the obervations planned in the context of the CHEOPS mission. Methods. As initial condition, we have assumed that each star is characterized by just one orbiting planet. We built mock light curves that included a realistic stellar activity pattern, the reflected light component of the planet and an instrumental noise level, which we have chosen to be at the same level as predicted for CHEOPS. We then fit these light curves to try to recover the reflected light component, assuming the activity patterns can be modeled with a Gaussian process. Results. We estimate that at least one full stellar rotation is necessary to obtain a reliable detection of the planetary albedo. This result is independent of the level of noise, but it depends on the limitation of the Gaussian process to describe the stellar activity when the light curve time-span is shorter than the stellar rotation. As an additional result, we found that with a 6.5 magnitude star and the noise level of CHEOPS, it is possible to detect the planetary albedo up to a lower limit of Rp = 0.03 R*. Finally, in presence of typical CHEOPS gaps in the simulations, we confirm that it is still possible to obtain a reliable albedo.

scholarly journals juliet: a versatile modelling tool for transiting and non-transiting exoplanetary systems

2019 ◽  
Vol 490 (2) ◽  
pp. 2262-2283 ◽  
Author(s):  
Néstor Espinoza ◽  
Diana Kossakowski ◽  
Rafael Brahm
Keyword(s):  
Radial Velocity ◽  
Model Comparison ◽  
Computing Time ◽  
Radial Velocities ◽  
Stellar Rotation ◽  
Velocity Measurements ◽  
Nested Sampling ◽  
Rotation Periods ◽  
Exoplanetary Systems ◽  
Versatile Tool

ABSTRACT Here we present juliet, a versatile tool for the analysis of transits, radial velocities, or both. juliet is built over many available tools for the modelling of transits, radial velocities, and stochastic processes (here modelled as Gaussian Processes; GPs) in order to deliver a tool/wrapper which can be used for the analysis of transit photometry and radial-velocity measurements from multiple instruments at the same time, using nested sampling algorithms which allows it to not only perform a thorough sampling of the parameter space, but also to perform model comparison via Bayesian evidences. In addition, juliet allows us to fit transiting and non-transiting multiplanetary systems, and to fit GPs which might share hyperparameters between the photometry and radial velocities simultaneously (e.g. stellar rotation periods), which might be useful for disentangling stellar activity in radial-velocity measurements. Nested Sampling, Importance Nested Sampling, and Dynamic Nested Sampling is performed with publicly available codes which in turn give juliet multithreading options, allowing it to scale the computing time of complicated multidimensional problems. We make juliet publicly available via GitHub.

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 Spectroscopic membership for the populous 300 Myr-old open cluster NGC 3532

2019 ◽  
Vol 622 ◽  
pp. A110 ◽  
Author(s):  
D. J. Fritzewski ◽  
S. A. Barnes ◽  
D. J. James ◽  
A. M. Geller ◽  
S. Meibom ◽  
...  
Keyword(s):  
Radial Velocity ◽  
Galactic Plane ◽  
Open Cluster ◽  
Mass Range ◽  
Open Clusters ◽  
Radial Velocities ◽  
Stellar Rotation ◽  
Low Mass Stars ◽  
Giant Stars ◽  
Cluster Sequence

Context. NGC 3532 is an extremely rich open cluster embedded in the Galactic disc, hitherto lacking a comprehensive, documented membership list. Aims. We provide membership probabilities from new radial velocity observations of solar-type and low-mass stars in NGC 3532, in part as a prelude to a subsequent study of stellar rotation in the cluster. Methods. Using extant optical and infra-red photometry we constructed a preliminary photometric membership catalogue, consisting of 2230 dwarf and turn-off stars. We selected 1060 of these for observation with the AAOmega spectrograph at the 3.9 m-Anglo-Australian Telescope and 391 stars for observations with the Hydra-South spectrograph at the 4 m Victor Blanco Telescope, obtaining spectroscopic observations over a decade for 145 stars. We measured radial velocities for our targets through cross-correlation with model spectra and standard stars, and supplemented them with radial velocities for 433 additional stars from the literature. We also measured log g, Teff, and [Fe/H] from the AAOmega spectra. Results. The radial velocity distribution emerging from the observations is centred at 5.43 ± 0.04 km s−1 and has a width (standard deviation) of 1.46 km s−1. Together with proper motions from Gaia DR2 we find 660 exclusive members, of which five are likely binary members. The members are distributed across the whole cluster sequence, from giant stars to M dwarfs, making NGC 3532 one of the richest Galactic open clusters known to date, on par with the Pleiades. From further spectroscopic analysis of 153 dwarf members we find the metallicity to be marginally sub-solar, with [Fe/H] = −0.07 ± 0.10. We confirm the extremely low reddening of the cluster, EB − V = 0.034 ± 0.012 mag, despite its location near the Galactic plane. Exploiting trigonometric parallax measurements from Gaia DR2 we find a distance of 48435−30 pc [(m − M)0 = 8.42 ± 0.14 mag]. Based on the membership we provide an empirical cluster sequence in multiple photometric passbands. A comparison of the photometry of the measured cluster members with several recent model isochrones enables us to confirm the 300 Myr cluster age. However, all of the models evince departures from the cluster sequence in particular regions, especially in the lower mass range.

Commission 30: Radial Velocities: (Vitesses Radiales)

2000 ◽  
Vol 24 (1) ◽  
pp. 338-345
Author(s):  
J.B. Hearnshaw ◽  
A.A. Tokovinin ◽  
W.D. Cochran ◽  
F.C. Fekel ◽  
T. Mazeh ◽  
...  
Keyword(s):  
Variable Stars ◽  
Radial Velocities ◽  
Stellar Atmospheres ◽  
Spectroscopic Binaries ◽  
Electromagnetic Spectrum ◽  
Stellar Rotation ◽  
New Members ◽  
The Past ◽  
Pulsating Variable Stars ◽  
Wide Range

Commission 30 has 120 members in 28 countries who are active in the area of radial velocities. During the past triennium 11 new members have joined the commission. The work of the commission covers a wide range of topics all of which concern the application of the Doppler effect to astronomical objects, including galaxies and the interstellar medium as well as stars, and in all wavelength ranges of the electromagnetic spectrum. Although the commission focuses mainly on stellar and galaxy radial velocities, it is noted that stellar rotation, spectroscopic binaries, extrasolar planet searches, pulsating variable stars, asteroseismology and turbulence in stellar atmospheres are also included.

Integrated Fractional white Noise as an Alternative to Multifractional Brownian Motion

2007 ◽  
Vol 44 (02) ◽  
pp. 393-408 ◽  
Author(s):  
Allan Sly
Keyword(s):  
Stochastic Process ◽  
Brownian Motion ◽  
White Noise ◽  
Gaussian Process ◽  
Discrete Data ◽  
Hölder Exponent ◽  
Scaling Properties ◽  
Multifractional Brownian Motion ◽  
Local Properties

Multifractional Brownian motion is a Gaussian process which has changing scaling properties generated by varying the local Hölder exponent. We show that multifractional Brownian motion is very sensitive to changes in the selected Hölder exponent and has extreme changes in magnitude. We suggest an alternative stochastic process, called integrated fractional white noise, which retains the important local properties but avoids the undesirable oscillations in magnitude. We also show how the Hölder exponent can be estimated locally from discrete data in this model.

On the Inhomogeneity of Chemical Composition over the Surface of 21 Per

1976 ◽  
Vol 32 ◽  
pp. 343-349
Author(s):  
Yu.V. Glagolevsky ◽  
K.I. Kozlova ◽  
V.S. Lebedev ◽  
N.S. Polosukhina
Keyword(s):  
Chemical Composition ◽  
Spectral Line ◽  
Variable Star ◽  
Radial Velocities ◽  
Crimean Astrophysical Observatory ◽  
Line Intensities ◽  
Magnetic Variable

SummaryThe magnetic variable star 21 Per has been studied from 4 and 8 Å/mm spectra obtained with the 2.6 - meter reflector of the Crimean Astrophysical Observatory. Spectral line intensities (Wλ) and radial velocities (Vr) have been measured.

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