scholarly journals Radial velocity follow-up of GJ1132 with HARPS

2018 ◽  
Vol 618 ◽  
pp. A142 ◽  
Author(s):  
X. Bonfils ◽  
J.-M. Almenara ◽  
R. Cloutier ◽  
A. Wünsche ◽  
N. Astudillo-Defru ◽  
...  
Keyword(s):  
Radial Velocity ◽  
A Priori ◽  
Equilibrium Temperature ◽  
Correlated Noise ◽  
Minimum Mass ◽  
Stellar Rotation ◽  
Stellar Activity ◽  
Orbital Parameters ◽  
The Status

The source GJ1132 is a nearby red dwarf known to host a transiting Earth-size planet. After its initial detection, we pursued an intense follow-up with the HARPS velocimeter. We now confirm the detection of GJ1132b with radial velocities alone. We refined its orbital parameters, and in particular, its mass (mb = 1.66 ± 0.23 M⊕), density (ρb = 6.3 ± 1.3 g cm−3), and eccentricity (eb < 0.22; 95%). We also detected at least one more planet in the system. GJ1132c is a super-Earth with period Pc = 8.93 ± 0.01 days and minimum mass mc sinic = 2.64 ± 0.44 M⊕. Receiving about 1.9 times more flux than Earth in our solar system, its equilibrium temperature is that of a temperate planet (Teq = 230−300 K for albedos A = 0.75 − 0.00), which places GJ1132c near the inner edge of the so-called habitable zone. Despite an a priori favorable orientation for the system, Spitzer observations reject most transit configurations, leaving a posterior probability <1% that GJ1132c transits. GJ1132(d) is a third signal with period Pd = 177 ± 5 days attributed to either a planet candidate with minimum mass md sin id = 8.4−2.5+1.7 M⊕ or stellar activity. Its Doppler signal is the most powerful in our HARPS time series but appears on a timescale where either the stellar rotation or a magnetic cycle are viable alternatives to the planet hypothesis. On the one hand, the period is different than that measured for the stellar rotation (~125 days), and a Bayesian statistical analysis we performed with a Markov chain Monte Carlo and Gaussian processes demonstrates that the signal is better described by a Keplerian function than by correlated noise. On the other hand, periodograms of spectral indices sensitive to stellar activity show power excess at similar periods to that of this third signal, and radial velocity shifts induced by stellar activity can also match a Keplerian function. We, therefore, prefer to leave the status of GJ1132(d) undecided.

scholarly journals HADES RV program with HARPS-N at the TNG

2019 ◽  
Vol 622 ◽  
pp. A193 ◽  
Author(s):  
L. Affer ◽  
M. Damasso ◽  
G. Micela ◽  
E. Poretti ◽  
G. Scandariato ◽  
...  
Keyword(s):  
Rotation Period ◽  
Activity Cycle ◽  
Physical Parameters ◽  
Correlated Noise ◽  
Minimum Mass ◽  
Stellar Rotation ◽  
Orbital Parameters ◽  
Photometric Observations ◽  
Depth Analysis ◽  
Low Mass

Aims. The HArps-n red Dwarf Exoplanet Survey (HADES) is providing a major contribution to the widening of the current statistics of low-mass planets, through the in-depth analysis of precise radial-velocity (RV) measurements in a narrow range of spectral sub-types. Using the HARPS-N spectrograph we reach the precision needed to detect small planets with a few earth masses. Our survey is mainly focused on the M-dwarf population of the northern hemisphere. Methods. As part of that program, we obtained RV measurements of Gl 686, an M1 dwarf at d = 8.2 pc. These measurements show a dispersion much in excess of their internal errors. The analysis of data obtained within an intensive observing campaign demonstrates that the excess dispersion is due to a coherent signal with a period of 15.53 d. Almost simultaneous photometric observations were carried out within the APACHE and EXORAP programs to characterize the stellar activity and to distinguish periodic variations related to activity from signals due to the presence of planetary companions, complemented also with ASAS photometric data. We used a Bayesian framework to estimate the orbital parameters and the planet minimum mass, and to properly treat the activity noise. We took advantage of the available RV measurements for this target from other observing campaigns. The analysis of the RV composite time series from the HIRES, HARPS, and HARPS-N spectrographs, consisting of 198 measurements taken over 20 yr, enabled us to address the nature of periodic signals and also to characterize stellar physical parameters (mass, temperature, and rotation). Results. We report the discovery of a super-Earth orbiting at a distance of 0.092 AU from the host star Gl 686. The planet has a minimum mass of 7.1 ± 0.9 M⊕ and an orbital period of 15.532 ± 0.002 d. The analysis of the activity indexes, of the correlated noise through a Gaussian process framework, and of the photometry provides an estimate of the stellar rotation period at 37 d, and highlights the variability of the spot configuration during the long timespan covering 20 yr. The observed periodicities around 2000 d likely point to the existence of an activity cycle.

scholarly journals The CARMENES search for exoplanets around M dwarfs

2019 ◽  
Vol 627 ◽  
pp. A116 ◽  
Author(s):  
S. Lalitha ◽  
D. Baroch ◽  
J. C. Morales ◽  
V. M. Passegger ◽  
F. F. Bauer ◽  
...  
Keyword(s):  
Near Infrared ◽  
Correlated Noise ◽  
Stellar Rotation ◽  
M Dwarfs ◽  
Stellar Activity ◽  
Orbital Parameters ◽  
Rotation Periods ◽  
Planetary Mass ◽  
Low Mass ◽  
Orbital Periods

Although M dwarfs are known for high levels of stellar activity, they are ideal targets for the search of low-mass exoplanets with the radial velocity (RV) method. We report the discovery of a planetary-mass companion around LSPM J2116+0234 (M3.0 V) and confirm the existence of a planet orbiting GJ 686 (BD+18 3421; M1.0 V). The discovery of the planet around LSPM J2116+0234 is based on CARMENES RV observations in the visual and near-infrared channels. We confirm the planet orbiting around GJ 686 by analyzing the RV data spanning over two decades of observationsfrom CARMENES VIS, HARPS-N, HARPS, and HIRES. We find planetary signals at 14.44 and 15.53 d in the RV data for LSPM J2116+0234 and GJ 686, respectively. Additionally, the RV, photometric time series, and various spectroscopic indicators show hints of variations of 42 d for LSPM J2116+0234 and 37 d for GJ 686, which we attribute to the stellar rotation periods. The orbital parameters of the planets are modeled with Keplerian fits together with correlated noise from the stellar activity. A mini-Neptune with a minimum mass of 11.8 M⊕ orbits LSPM J2116+0234 producing a RV semi-amplitude of 6.19 m s−1, while a super-Earth of mass 6.6 M⊕ orbits GJ 686 and produces a RV semi-amplitude of 3.0 m s−1. Both LSPM J2116+0234 and GJ 686 have planetary companions populating the regime of exoplanets with masses lower than 15 M⊕ and orbital periods <20 d.

scholarly journals Biases in retrieving planetary signals in the presence of quasi-periodic stellar activity

2019 ◽  
Vol 489 (2) ◽  
pp. 2555-2571 ◽  
Author(s):  
M Damasso ◽  
M Pinamonti ◽  
G Scandariato ◽  
A Sozzetti
Keyword(s):  
Time Series ◽  
Gaussian Process Regression ◽  
Data Sets ◽  
Correlated Noise ◽  
Stellar Activity ◽  
Activity Component ◽  
Low Mass ◽  
Host Stars ◽  
Correlated Signals

Abstract Gaussian process regression is a widespread tool used to mitigate stellar correlated noise in radial velocity (RV) time series. It is particularly useful to search for and determine the properties of signals induced by small-sized low-mass planets (Rp < 4 R⊕, mp < 10 M⊕). By using extensive simulations based on a quasi-periodic representation of the stellar activity component, we investigate the ability in retrieving the planetary parameters in 16 different realistic scenarios. We analyse systems composed by one planet and host stars having different levels of activity, focusing on the challenging case represented by low-mass planets, with Doppler semi-amplitudes in the range 1–3 $\rm{\,m\,s^{-1}}$. We consider many different configurations for the quasi-periodic stellar activity component, as well as different combinations of the observing epochs. We use commonly employed analysis tools to search for and characterize the planetary signals in the data sets. The goal of our injection-recovery statistical analysis is twofold. First, we focus on the problem of planet mass determination. Then, we analyse in a statistical way periodograms obtained with three different algorithms, in order to explore some of their general properties, as the completeness and reliability in retrieving the injected planetary and stellar activity signals with low false alarm probabilities. This work is intended to provide some understanding of the biases introduced in the planet parameters inferred from the analysis of RV time series that contain correlated signals due to stellar activity. It also aims to motivate the use and encourage the improvement of extensive simulations for planning spectroscopic follow-up observations.

scholarly journals Disentangling planetary orbits from stellar activity in radial-velocity surveys

2014 ◽  
Vol 13 (2) ◽  
pp. 155-157 ◽  
Author(s):  
R. D. Haywood ◽  
A. Collier Cameron ◽  
D. Queloz ◽  
S.C.C. Barros ◽  
M. Deleuil ◽  
...  
Keyword(s):  
Radial Velocity ◽  
High Accuracy ◽  
Stellar Surface ◽  
Stellar Activity ◽  
The Earth ◽  
Planetary Orbits ◽  
Low Mass ◽  
Do So

AbstractThe majority of extra-solar planets have been discovered (or confirmed after follow-up) through radial-velocity (RV) surveys. Using ground-based spectrographs such as High Accuracy Radial Velocity Planetary Search (HARPS) and HARPS-North, it is now possible to detect planets that are only a few times the mass of the Earth. However, the presence of dark spots on the stellar surface produces RV signals that are very similar in amplitude to those caused by orbiting low-mass planets. Disentangling these signals has thus become the biggest challenge in the detection of Earth-mass planets using RV surveys. To do so, we use the star's lightcurve to model the RV variations produced by spots. Here we present this method and show the results of its application to CoRoT-7.

scholarly journals The GAPS Programme at TNG

2020 ◽  
Vol 638 ◽  
pp. A5 ◽  
Author(s):  
I. Carleo ◽  
L. Malavolta ◽  
A. F. Lanza ◽  
M. Damasso ◽  
S. Desidera ◽  
...  
Keyword(s):  
Radial Velocity ◽  
Near Infrared ◽  
Semimajor Axis ◽  
Young Stars ◽  
Homogeneous Sample ◽  
Stellar Activity ◽  
Orbital Parameters ◽  
Hot Jupiters ◽  
Multi Band ◽  
Hot Jupiter

Context. The existence of hot Jupiters is still not well understood. Two main channels are thought to be responsible for their current location: a smooth planet migration through the protoplanetary disk or the circularization of an initial highly eccentric orbit by tidal dissipation leading to a strong decrease in the semimajor axis. Different formation scenarios result in different observable effects, such as orbital parameters (obliquity and eccentricity) or frequency of planets at different stellar ages. Aims. In the context of the GAPS Young Objects project, we are carrying out a radial velocity survey with the aim of searching and characterizing young hot-Jupiter planets. Our purpose is to put constraints on evolutionary models and establish statistical properties, such as the frequency of these planets from a homogeneous sample. Methods. Since young stars are in general magnetically very active, we performed multi-band (visible and near-infrared) spectroscopy with simultaneous GIANO-B + HARPS-N (GIARPS) observing mode at TNG. This helps in dealing with stellar activity and distinguishing the nature of radial velocity variations: stellar activity will introduce a wavelength-dependent radial velocity amplitude, whereas a Keplerian signal is achromatic. As a pilot study, we present here the cases of two known hot Jupiters orbiting young stars: HD 285507 b and AD Leo b. Results. Our analysis of simultaneous high-precision GIARPS spectroscopic data confirms the Keplerian nature of the variation in the HD 285507 radial velocities and refines the orbital parameters of the hot Jupiter, obtaining an eccentricity consistent with a circular orbit. Instead, our analysis does not confirm the signal previously attributed to a planet orbiting AD Leo. This demonstrates the power of the multi-band spectroscopic technique when observing active stars.

scholarly journals Revisiting Proxima with ESPRESSO

2020 ◽  
Vol 639 ◽  
pp. A77 ◽  
Author(s):  
A. Suárez Mascareño ◽  
J. P. Faria ◽  
P. Figueira ◽  
C. Lovis ◽  
M. Damasso ◽  
...  
Keyword(s):  
Correlation Function ◽  
Radial Velocity ◽  
Cross Correlation ◽  
Full Width Half Maximum ◽  
Cross Correlation Function ◽  
Minimum Mass ◽  
Full Width ◽  
Half Maximum ◽  
Stellar Activity ◽  
The Cross

Context. The discovery of Proxima b marked one of the most important milestones in exoplanetary science in recent years. Yet the limited precision of the available radial velocity data and the difficulty in modelling the stellar activity calls for a confirmation of the Earth-mass planet. Aims. We aim to confirm the presence of Proxima b using independent measurements obtained with the new ESPRESSO spectrograph, and refine the planetary parameters taking advantage of its improved precision. Methods. We analysed 63 spectroscopic ESPRESSO observations of Proxima (Gl 551) taken during 2019. We obtained radial velocity measurements with a typical radial velocity photon noise of 26 cm s−1. We combined these data with archival spectroscopic observations and newly obtained photometric measurements to model the stellar activity signals and disentangle them from planetary signals in the radial velocity (RV) data. We ran a joint Markov chain Monte Carlo analysis on the time series of the RV and full width half maximum of the cross-correlation function to model the planetary and stellar signals present in the data, applying Gaussian process regression to deal with the stellar activity signals. Results. We confirm the presence of Proxima b independently in the ESPRESSO data and in the combined ESPRESSO+ HARPS+UVES dataset. The ESPRESSO data on its own shows Proxima b at a period of 11.218 ± 0.029 days, with a minimum mass of 1.29 ± 0.13 M⊕. In the combined dataset we measure a period of 11.18427 ± 0.00070 days with a minimum mass of 1.173 ± 0.086 M⊕. We get a clear measurement of the stellar rotation period (87 ± 12 d) and its induced RV signal, but no evidence of stellar activity as a potential cause for the 11.2 days signal. We find some evidence for the presence of a second short-period signal, at 5.15 days with a semi-amplitude of only 40 cm s−1. If caused by a planetary companion, it would correspond to a minimum mass of 0.29 ± 0.08 M⊕. We find that forthe case of Proxima, the full width half maximum of the cross-correlation function can be used as a proxy for the brightness changes and that its gradient with time can be used to successfully detrend the RV data from part of the influence of stellar activity. The activity-induced RV signal in the ESPRESSO data shows a trend in amplitude towards redder wavelengths. Velocities measured using the red end of the spectrograph are less affected by activity, suggesting that the stellar activity is spot dominated. This could be used to create differential RVs that are activity dominated and can be used to disentangle activity-induced and planetary-induced signals. The data collected excludes the presence of extra companions with masses above 0.6 M⊕ at periods shorter than 50 days.

scholarly journals Periodic transit timing variations and refined system parameters of the exoplanet XO-6b

2019 ◽  
Author(s):  
Zoltán Garai ◽  
Theodor Pribulla ◽  
Richard Komžík ◽  
Emil Kundra ◽  
Ľubomír Hambálek ◽  
...  
Keyword(s):  
Radial Velocity ◽  
Rotating Stars ◽  
Velocity Measurements ◽  
Orbital Parameters ◽  
Orbit Inclination ◽  
Consistent Solution ◽  
Low Mass ◽  
Academy Of Sciences ◽  
Fast Rotating

Abstract Only a few exoplanets are known to orbit around fast rotating stars. One of them is XO-6b, which orbits an F5V-type star. Shortly after the discovery, we started multicolor photometric and radial-velocity follow-up observations of XO-6b, using the telescopes of Astronomical Institute of the Slovak Academy of Sciences. Our main scientific goals were to better characterize the planetary system and to search for transit timing variations. We refined several planetary and orbital parameters. Based on our measurements, the planet XO-6b seems to be about 10% larger, which is, however, only about 2σ difference, but its orbit inclination angle, with respect to the plane of the sky, seems to be significantly smaller, than it was determined originally by the discoverers. In this case we found about 9.5σ difference. Moreover, we observed periodic transit timing variations of XO-6b with a semi-amplitude of about 14 min and with a period of about 450 days. There are two plausible explanations of such transit timing variations: (1) a third object in the system XO-6 causing light-time effect, or (2) resonant perturbations between the transiting planet XO-6b and another unknown low-mass planet in this system. From the O-C diagram we derived that the assumed third object in the system should have a stellar mass, therefore significant variations are expected in the radial-velocity measurements of XO-6. Since this is not the case, and since all attempts to fit radial velocities and O-C data simultaneously failed to provide a consistent solution, more realistic is the second explanation.

The Next Generation Transit Survey

2017 ◽  
Vol 14 (S339) ◽  
pp. 22-22
Author(s):  
M. Burleigh
Keyword(s):  
Radial Velocity ◽  
Mass Determination ◽  
Next Generation ◽  
M Dwarfs ◽  
Early Results ◽  
The Status

AbstractThis talk introduced and described the Next Generation Transit Survey (NGTS), which is a new ground-based transit survey operating at the ESO Paranal Observatory. NGTS has been designed to achieve better photometric precision than previous ground-based surveys; it aims to detect Neptune-sized planets around Sun-like stars, and sub-Neptunes around M dwarfs that are sufficiently bright for radial-velocity confirmation and mass determination. NGTS is also optimised for ground-based follow up of exoplanet candidates from TESS and PLATO. I presented early results from the survey, and described the status of our HARPS radial-velocity and SAAO photometric follow-ups of exoplanet candidates.

scholarly journals Stellar activity of planetary host star HD 189733

2008 ◽  
Vol 4 (S253) ◽  
pp. 462-465
Author(s):  
I. Boisse ◽  
C. Moutou ◽  
A. Vidal-Madjar ◽  
F. Bouchy ◽  
F. Pont ◽  
...  
Keyword(s):  
High Resolution ◽  
Radial Velocity ◽  
High Precision ◽  
Velocity Gradient ◽  
Orbital Motion ◽  
Spectral Lines ◽  
Stellar Surface ◽  
Stellar Activity ◽  
Orbital Parameters

AbstractExoplanet search programs need to study how to disentangle radial-velocity (RV) variations due to Doppler motion and the noise induced by stellar activity. We monitored the active K2V HD 189733 with the high-resolution SOPHIE spectrograph (OHP, France). We refined the orbital parameters of HD 189733b and put limitations on the eccentricity and on a long-term velocity gradient. We subtracted the orbital motion of the planet and compared the variability of activity spectroscopic indices (HeI, Hα, Ca II H&K lines) to the evolution of the RV residuals and the shape of spectral lines. All are in agreement with an active stellar surface in rotation. We used such correlations to correct for the RV jitter due to stellar activity. This results in achieving a high precision on the orbital parameters, with a semi-amplitude: K=200.56±0.88m⋅s−1 and a derived planet mass of MP=1.13±0.03 MJup.

scholarly journals Early science with SPIRou: near-infrared radial velocity and spectropolarimetry of the planet-hosting star HD 189733

2020 ◽  
Vol 642 ◽  
pp. A72 ◽  
Author(s):  
C. Moutou ◽  
S. Dalal ◽  
J.-F. Donati ◽  
E. Martioli ◽  
C. P. Folsom ◽  
...  
Keyword(s):  
Magnetic Flux ◽  
Radial Velocity ◽  
Large Scale ◽  
Near Infrared ◽  
Field Studies ◽  
High Spectral Resolution ◽  
Planetary Orbit ◽  
Dominant Factor ◽  
Stellar Activity ◽  
Orbital Parameters

SPIRou is the newest spectropolarimeter and high-precision velocimeter that has recently been installed at the Canada-France-Hawaii Telescope on Maunakea, Hawaii. It operates in the near-infrared and simultaneously covers the 0.98–2.35 μm domain at high spectral resolution. SPIRou is optimized for exoplanet search and characterization with the radial-velocity technique, and for polarization measurements in stellar lines and subsequent magnetic field studies. The host of the transiting hot Jupiter HD 189733 b has been observed during early science runs. We present the first near-infrared spectropolarimetric observations of the planet-hosting star as well as the stellar radial velocities as measured by SPIRou throughout the planetary orbit and two transit sequences. The planetary orbit and Rossiter-McLaughlin anomaly are both investigated and modeled. The orbital parameters and obliquity are all compatible with the values found in the optical. The obtained radial-velocity precision is compatible with about twice the photon-noise estimates for a K2 star under these conditions. The additional scatter around the orbit, of about 8 m s−1, agrees with previous results that showed that the activity-induced scatter is the dominant factor. We analyzed the polarimetric signal, Zeeman broadening, and chromospheric activity tracers such as the 1083nm HeI and the 1282nm Paβ lines to investigate stellar activity. First estimates of the average unsigned magnetic flux from the Zeeman broadening of the FeI lines give a magnetic flux of 290 ± 58 G, and the large-scale longitudinal field shows typical values of a few Gauss. These observations illustrate the potential of SPIRou for exoplanet characterization and magnetic and stellar activity studies.

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