Simulated mass measurements of the young planet K2-33b

ABSTRACT In this paper, we carry out simulations of radial velocity (RV) measurements of the mass of the 8–11 Myr Neptune-sized planet K2-33b using high-precision near-infrared velocimeters like SPIRou at the Canada–France–Hawaii Telescope. We generate an RV curve containing a planet signature and a realistic stellar activity signal, computed for a central wavelength of 1.8 µm and statistically compatible with the light curve obtained with K2. The modelled activity signal includes the effect of time-evolving dark and bright surface features hosting a 2 kG radial magnetic field, resulting in an RV signal of semi-amplitude ∼30 m s−1. Assuming a 3-month visibility window, we build RV time series including Gaussian white noise from which we retrieve the planet mass while filtering the stellar activity signal using Gaussian process regression. We find that 35/50 visits spread over three consecutive bright-time runs on K2-33 allow one to reliably detect planet RV signatures of, respectively, 10 and 5 m s−1 at precisions >3σ. We also show that 30 visits may end up being insufficient in some cases to provide a good coverage of the stellar rotation cycle, with the result that the planet signature can go undetected or the mass estimation be plagued by large errors.

Download Full-text

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

Astronomy and Astrophysics ◽

10.1051/0004-6361/201732459 ◽

2018 ◽

Vol 615 ◽

pp. A69 ◽

Cited By ~ 15

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.

Download Full-text

The CARMENES search for exoplanets around M dwarfs

Astronomy and Astrophysics ◽

10.1051/0004-6361/201935534 ◽

2019 ◽

Vol 627 ◽

pp. A116 ◽

Cited By ~ 4

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.

Download Full-text

The CARMENES search for exoplanets around M dwarfs

Astronomy and Astrophysics ◽

10.1051/0004-6361/202038820 ◽

2020 ◽

Vol 643 ◽

pp. A112

Author(s):

S. Stock ◽

E. Nagel ◽

J. Kemmer ◽

V. M. Passegger ◽

S. Reffert ◽

...

Keyword(s):

Gaussian Process Regression ◽

Stellar Rotation ◽

M Dwarfs ◽

Stellar Activity ◽

Rotation Periods ◽

Photometric Observations ◽

Orbital Periods ◽

Stellar Properties ◽

Core Accretion ◽

Common Architecture

We announce the discovery of two planets orbiting the M dwarfs GJ 251 (0.360 ± 0.015M⊙) and HD 238090 (0.578 ± 0.021M⊙) based on CARMENES radial velocity (RV) data. In addition, we independently confirm with CARMENES data the existence of Lalande 21185 b, a planet that has recently been discovered with the SOPHIE spectrograph. All three planets belong to the class of warm or temperate super-Earths and share similar properties. The orbital periods are 14.24 d, 13.67 d, and 12.95 d and the minimum masses are 4.0 ± 0.4 M⊕, 6.9 ± 0.9 M⊕, and 2.7 ± 0.3 M⊕ for GJ 251 b, HD 238090 b, and Lalande 21185 b, respectively. Based on the orbital and stellar properties, we estimate equilibrium temperatures of 351.0 ± 1.4 K for GJ 251 b, 469.6 ± 2.6 K for HD 238090 b, and 370.1 ± 6.8 K for Lalande 21185 b. For the latter we resolve the daily aliases that were present in the SOPHIE data and that hindered an unambiguous determination of the orbital period. We find no significant signals in any of our spectral activity indicators at the planetary periods. The RV observations were accompanied by contemporaneous photometric observations. We derive stellar rotation periods of 122.1 ± 2.2 d and 96.7 ± 3.7 d for GJ 251 and HD 238090, respectively. The RV data of all three stars exhibit significant signals at the rotational period or its first harmonic. For GJ 251 and Lalande 21185, we also find long-period signals around 600 d, and 2900 d, respectively, which we tentatively attribute to long-term magnetic cycles. We apply a Bayesian approach to carefully model the Keplerian signals simultaneously with the stellar activity using Gaussian process regression models and extensively search for additional significant planetary signals hidden behind the stellar activity. Current planet formation theories suggest that the three systems represent a common architecture, consistent with formation following the core accretion paradigm.

Download Full-text

The GAPS programme at TNG

Astronomy and Astrophysics ◽

10.1051/0004-6361/202037939 ◽

2020 ◽

Vol 639 ◽

pp. A50 ◽

Cited By ~ 2

Author(s):

S. Benatti ◽

M. Damasso ◽

S. Desidera ◽

F. Marzari ◽

K. Biazzo ◽

...

Keyword(s):

Time Series ◽

Rotation Period ◽

Giant Planet ◽

Gaussian Process Regression ◽

Major Axis ◽

Dynamical Analysis ◽

Minimum Mass ◽

Stellar Rotation ◽

Semi Major Axis ◽

Stellar Activity

Context. Observations of exoplanetary systems demonstrate that a wide variety of planetary architectures are possible. Determining the rate of occurrence of Solar System analogues – with inner terrestrial planets and outer gas giants – remains an open question. Aims. Within the framework of the Global Architecture of Planetary Systems (GAPS) project, we collected more than 300 spectra with HARPS-N at the Telescopio Nazionale Galileo for the bright G9V star HD 164922. This target is known to host one gas giant planet in a wide orbit (Pb ~1200 days, semi-major axis ~ 2 au) and a Neptune-mass planet with a period of Pc ~76 days. We aimed to investigate the presence of additional low-mass companions in the inner region of the system. Methods. We compared the radial velocities (RV) and the activity indices derived from the HARPS-N time series to measure the rotation period of the star and used a Gaussian process regression to describe the behaviour of the stellar activity. We then combined a model of planetary and stellar activity signals in an RV time series composed of almost 700 high-precision RVs, both from HARPS-N and literature data. We performed a dynamical analysis to evaluate the stability of the system and the allowed regions for additional potential companions. We performed experiments on the injection and recovery of additional planetary signals to gauge the sensitivity thresholds in minimum mass and orbital separation imposed by our data. Results. Thanks to the high sensitivity of the HARPS-N dataset, we detected an additional inner super-Earth with an RV semi-amplitude of 1.3 ± 0.2 m s−1 and a minimum mass of md sin i = 4 ± 1 M⊕. It orbits HD 164922 with a period of 12.458 ± 0.003 days. We disentangled the planetary signal from activity and measured a stellar rotation period of ~ 42 days. The dynamical analysis shows the long-term stability of the orbits of the three-planet system and allows us to identify the permitted regions for additional planets in the semi-major axis ranges 0.18–0.21 au and 0.6–1.4 au. The latter partially includes the habitable zone of the system. We did not detect any planet in these regions, down to minimum detectable masses of 5 and 18 M⊕, respectively. A larger region of allowed planets is expected beyond the orbit of planet b, where our sampling rules out bodies with minimum mass >50 M⊕. The planetary orbital parameters and the location of the snow line suggest that this system has been shaped by a gas disk migration process that halted after its dissipation.

Download Full-text

Central kiloparsec of NGC 1326 observed with SINFONI

Astronomy and Astrophysics ◽

10.1051/0004-6361/201936451 ◽

2020 ◽

Vol 638 ◽

pp. A53

Author(s):

Nastaran Fazeli ◽

Gerold Busch ◽

Andreas Eckart ◽

Françoise Combes ◽

Persis Misquitta ◽

...

Keyword(s):

Black Hole ◽

Galaxy Evolution ◽

Near Infrared ◽

Velocity Fields ◽

Molecular Gas ◽

Nearby Galaxy ◽

Stellar Content ◽

Stellar Rotation ◽

Supermassive Black Hole ◽

Integral Field Spectrograph

Gas inflow processes in the vicinity of galactic nuclei play a crucial role in galaxy evolution and supermassive black hole growth. Exploring the central kiloparsec of galaxies is essential to shed more light on this subject. We present near-infrared H- and K-band results of the nuclear region of the nearby galaxy NGC 1326, observed with the integral-field spectrograph SINFONI mounted on the Very Large Telescope. The field of view covers 9″ × 9″ (650 × 650 pc2). Our work is concentrated on excitation conditions, morphology, and stellar content. The nucleus of NGC 1326 was classified as a LINER, however in our data we observed an absence of ionised gas emission in the central r ∼ 3″. We studied the morphology by analysing the distribution of ionised and molecular gas, and thereby detected an elliptically shaped, circum-nuclear star-forming ring at a mean radius of 300 pc. We estimate the starburst regions in the ring to be young with dominating ages of < 10 Myr. The molecular gas distribution also reveals an elongated east to west central structure about 3″ in radius, where gas is excited by slow or mild shock mechanisms. We calculate the ionised gas mass of 8 × 105 M⊙ completely concentrated in the nuclear ring and the warm molecular gas mass of 187 M⊙, from which half is concentrated in the ring and the other half in the elongated central structure. The stellar velocity fields show pure rotation in the plane of the galaxy. The gas velocity fields show similar rotation in the ring, but in the central elongated H2 structure they show much higher amplitudes and indications of further deviation from the stellar rotation in the central 1″ aperture. We suggest that the central 6″ elongated H2 structure might be a fast-rotating central disc. The CO(3–2) emission observations with the Atacama Large Millimeter/submillimeter Array reveal a central 1″ torus. In the central 1″ of the H2 velocity field and residual maps, we find indications for a further decoupled structure closer to a nuclear disc, which could be identified with the torus surrounding the supermassive black hole.

Download Full-text

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

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz2216 ◽

2019 ◽

Vol 489 (2) ◽

pp. 2555-2571 ◽

Cited By ~ 3

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.

Download Full-text

Infrared spectroscopy of the merger candidate KIC 9832227

Astronomy and Astrophysics ◽

10.1051/0004-6361/201832717 ◽

2018 ◽

Vol 615 ◽

pp. A120 ◽

Cited By ~ 1

Author(s):

Ya. V. Pavlenko ◽

A. Evans ◽

D. P. K. Banerjee ◽

J. Southworth ◽

M. Shahbandeh ◽

...

Keyword(s):

Infrared Spectroscopy ◽

Near Infrared ◽

Binary Star ◽

Circumstellar Envelope ◽

Stellar Rotation ◽

Coronal Activity ◽

Orbital Phase ◽

Solar Metallicity ◽

Contact Binary ◽

The Individual

Context. It has been predicted that the object KIC 9832227 – a contact binary star – will undergo a merger in 2022.2 ± 0.7. We describe the near-infrared (NIR) spectrum of this object as an impetus to obtain pre-merger data. Aims. We aim to characterise (i) the nature of the individual components of the binary and (ii) the likely circumbinary environment, so that the merger – if and when it occurs – can be interpreted in an informed manner. Methods. We use infrared (IR) spectroscopy in the wavelength range 0.7–2.5 μm, to which we fit model atmospheres to represent the individual stars. We use the binary ephemeris to determine the orbital phase at the time of observation. Results. We find that the IR spectrum is best fitted by a single component with effective temperature 5920 K, log[g] = 4.1, and solar metallicity, consistent with the fact that the system was observed at conjunction. Conclusions. The strength of the IR H lines is consistent with a high value of logg, and the strength of the Ca II triplet indicates the presence of a chromosphere, as might be expected from rapid stellar rotation. The He I absorption we observe likely arises in He excited by coronal activity in a circumstellar envelope, suggesting that the weakness of the Ca II triplet is also likely chromospheric in origin.

Download Full-text

Tidal effects on stellar activity

Proceedings of the International Astronomical Union ◽

10.1017/s1743921317004045 ◽

2016 ◽

Vol 12 (S328) ◽

pp. 308-314

Author(s):

K. Poppenhaeger

Keyword(s):

Orbital Period ◽

Binary Systems ◽

Semimajor Axis ◽

Rotation Period ◽

Magnetic Activity ◽

Stellar Rotation ◽

Stellar Activity ◽

Tidal Interaction ◽

Hot Jupiters ◽

Orbital Periods

AbstractThe architecture of many exoplanetary systems is different from the solar system, with exoplanets being in close orbits around their host stars and having orbital periods of only a few days. We can expect interactions between the star and the exoplanet for such systems that are similar to the tidal interactions observed in close stellar binary systems. For the exoplanet, tidal interaction can lead to circularization of its orbit and the synchronization of its rotational and orbital period. For the host star, it has long been speculated if significant angular momentum transfer can take place between the planetary orbit and the stellar rotation. In the case of the Earth-Moon system, such tidal interaction has led to an increasing distance between Earth and Moon. For stars with Hot Jupiters, where the orbital period of the exoplanet is typically shorter than the stellar rotation period, one expects a decreasing semimajor axis for the planet and enhanced stellar rotation, leading to increased stellar activity. Also excess turbulence in the stellar convective zone due to rising and subsiding tidal bulges may change the magnetic activity we observe for the host star. I will review recent observational results on stellar activity and tidal interaction in the presence of close-in exoplanets, and discuss the effects of enhanced stellar activity on the exoplanets in such systems.

Download Full-text

The GAPS Programme at TNG

Astronomy and Astrophysics ◽

10.1051/0004-6361/201937369 ◽

2020 ◽

Vol 638 ◽

pp. A5 ◽

Cited By ~ 6

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.

Download Full-text

Diving Beneath the Sea of Stellar Activity: Chromatic Radial Velocities of the Young AU Mic Planetary System

The Astronomical Journal ◽

10.3847/1538-3881/ac2c80 ◽

2021 ◽

Vol 162 (6) ◽

pp. 295

Author(s):

Bryson L. Cale ◽

Michael Reefe ◽

Peter Plavchan ◽

Angelle Tanner ◽

Eric Gaidos ◽

...

Keyword(s):

Process Model ◽

Near Infrared ◽

Wavelength Dependence ◽

M Dwarfs ◽

Echelle Spectrograph ◽

Stellar Activity ◽

Transiting Planets ◽

Order Of Magnitude ◽

Modeling Toolkit ◽

M Dwarf

Abstract We present updated radial-velocity (RV) analyses of the AU Mic system. AU Mic is a young (22 Myr) early-M dwarf known to host two transiting planets—P b ∼ 8.46 days, R b = 4.38 − 0.18 + 0.18 R ⊕ , P c ∼ 18.86 days, R c = 3.51 − 0.16 + 0.16 R ⊕ . With visible RVs from Calar Alto high-Resolution search for M dwarfs with Exo-earths with Near-infrared and optical echelle Spectrographs (CARMENES)-VIS, CHIRON, HARPS, HIRES, Minerva-Australis, and Tillinghast Reflector Echelle Spectrograph, as well as near-infrared (NIR) RVs from CARMENES-NIR, CSHELL, IRD, iSHELL, NIRSPEC, and SPIRou, we provide a 5σ upper limit to the mass of AU Mic c of M c ≤ 20.13 M ⊕ and present a refined mass of AU Mic b of M b = 20.12 − 1.57 + 1.72 M ⊕ . Used in our analyses is a new RV modeling toolkit to exploit the wavelength dependence of stellar activity present in our RVs via wavelength-dependent Gaussian processes. By obtaining near-simultaneous visible and near-infrared RVs, we also compute the temporal evolution of RV “color” and introduce a regressional method to aid in isolating Keplerian from stellar activity signals when modeling RVs in future works. Using a multiwavelength Gaussian process model, we demonstrate the ability to recover injected planets at 5σ significance with semi-amplitudes down to ≈10 m s−1 with a known ephemeris, more than an order of magnitude below the stellar activity amplitude. However, we find that the accuracy of the recovered semi-amplitudes is ∼50% for such signals with our model.

Download Full-text