scholarly journals Magnetic fields in M dwarfs from the CARMENES survey

2019 ◽  
Vol 626 ◽  
pp. A86 ◽  
Author(s):  
D. Shulyak ◽  
A. Reiners ◽  
E. Nagel ◽  
L. Tal-Or ◽  
J. A. Caballero ◽  
...  
Keyword(s):  
Magnetic Fields ◽  
Near Infrared ◽  
Magnetic Energy ◽  
Spectral Lines ◽  
High Spectral Resolution ◽  
Stellar Rotation ◽  
M Dwarfs ◽  
Dynamo Action ◽  
Rotation Periods ◽  
Consistent Picture

Context. M dwarfs are known to generate the strongest magnetic fields among main-sequence stars with convective envelopes, but we are still lacking a consistent picture of the link between the magnetic fields and underlying dynamo mechanisms, rotation, and activity. Aims. In this work we aim to measure magnetic fields from the high-resolution near-infrared spectra taken with the CARMENES radial-velocity planet survey in a sample of 29 active M dwarfs and compare our results against stellar parameters. Methods. We used the state-of-the-art radiative transfer code to measure total magnetic flux densities from the Zeeman broadening of spectral lines and filling factors. Results. We detect strong kG magnetic fields in all our targets. In 16 stars the magnetic fields were measured for the first time. Our measurements are consistent with the magnetic field saturation in stars with rotation periods P < 4 d. The analysis of the magnetic filling factors reveal two different patterns of either very smooth distribution or a more patchy one, which can be connected to the dynamo state of the stars and/or stellar mass. Conclusions. Our measurements extend the list of M dwarfs with strong surface magnetic fields. They also allow us to better constrain the interplay between the magnetic energy, stellar rotation, and underlying dynamo action. The high spectral resolution and observations at near-infrared wavelengths are the beneficial capabilities of the CARMENES instrument that allow us to address important questions about the stellar magnetism.

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 SPIRou: NIR velocimetry and spectropolarimetry at the CFHT

2020 ◽  
Vol 498 (4) ◽  
pp. 5684-5703 ◽  
Author(s):  
J-F Donati ◽  
D Kouach ◽  
C Moutou ◽  
R Doyon ◽  
X Delfosse ◽  
...  
Keyword(s):  
Magnetic Fields ◽  
Near Infrared ◽  
Planetary Systems ◽  
Young Stars ◽  
Central Position ◽  
M Dwarfs ◽  
Testing Phase ◽  
First Results ◽  
New Generation ◽  
Final Acceptance

ABSTRACT This paper presents an overview of SPIRou, the new-generation near-infrared spectropolarimeter/precision velocimeter recently installed on the 3.6-m Canada–France–Hawaii Telescope (CFHT). Starting from the two main science goals, i.e., the quest for planetary systems around nearby M dwarfs and the study of magnetized star/planet formation, we outline the instrument concept that was designed to efficiently address these forefront topics, and detail the in-lab and on-sky instrument performances measured throughout the intensive testing phase that SPIRou was submitted to before passing the final acceptance review in early 2019 and initiating science observations. With a central position among the newly started programmes, the SPIRou Legacy Survey (SLS) Large Programme was allocated 300 CFHT nights until at least mid 2022. We also briefly describe a few of the first results obtained in the various science topics that SPIRou started investigating, focusing in particular on planetary systems of nearby M dwarfs, transiting exoplanets and their atmospheres, magnetic fields of young stars, but also on alternate science goals like the atmospheres of M dwarfs and the Earth’s atmosphere. We finally conclude on the key role that SPIRou and the CFHT can play in coordination with forthcoming major facilities like the JWST, the ELTs, PLATO, and ARIEL over the decade.

scholarly journals Direct numerical simulations of helical dynamo action: MHD and beyond

2004 ◽  
Vol 11 (5/6) ◽  
pp. 619-629 ◽  
Author(s):  
D. O. Gómez ◽  
P. D. Mininni
Keyword(s):  
Magnetic Fields ◽  
Numerical Simulations ◽  
Periodic Boundary ◽  
Incompressible Flows ◽  
Magnetic Energy ◽  
Periodic Boundary Conditions ◽  
Direct Numerical Simulations ◽  
Dynamo Action ◽  
Spatial Fluctuations ◽  
Kinetic Effects

Abstract. Magnetohydrodynamic dynamo action is often invoked to explain the existence of magnetic fields in several astronomical objects. In this work, we present direct numerical simulations of MHD helical dynamos, to study the exponential growth and saturation of magnetic fields. Simulations are made within the framework of incompressible flows and using periodic boundary conditions. The statistical properties of the flow are studied, and it is found that its helicity displays strong spatial fluctuations. Regions with large kinetic helicity are also strongly concentrated in space, forming elongated structures. In dynamo simulations using these flows, we found that the growth rate and the saturation level of magnetic energy and magnetic helicity reach an asymptotic value as the Reynolds number is increased. Finally, extensions of the MHD theory to include kinetic effects relevant in astrophysical environments are discussed.

scholarly journals The CARMENES search for exoplanets around M dwarfs

2019 ◽  
Vol 623 ◽  
pp. A24 ◽  
Author(s):  
B. Fuhrmeister ◽  
S. Czesla ◽  
J. H. M. M. Schmitt ◽  
E. N. Johnson ◽  
P. Schöfer ◽  
...  
Keyword(s):  
Gaussian Process ◽  
Near Infrared ◽  
Rotation Period ◽  
Gaussian Process Regression ◽  
Process Models ◽  
M Dwarfs ◽  
String Length ◽  
Phase Dispersion ◽  
Rotation Periods ◽  
Gaussian Process Models

We use spectra from CARMENES, the Calar Alto high-Resolution search for M dwarfs with Exo-earths with Near-infrared and optical Echelle Spectrographs, to search for periods in chromospheric indices in 16 M0–M2 dwarfs. We measure spectral indices in the Hα, the Ca II infrared triplet (IRT), and the Na I D lines to study which of these indices are best-suited to finding rotation periods in these stars. Moreover, we test a number of different period-search algorithms, namely the string length method, the phase dispersion minimisation, the generalized Lomb–Scargle periodogram, and the Gaussian process regression with quasi-periodic kernel. We find periods in four stars using Hα and in five stars using the Ca II IRT, two of which have not been found before. Our results show that both Hα and the Ca II IRT lines are well suited for period searches, with the Ca II IRT index performing slightly better than Hα. Unfortunately, the Na I D lines are strongly affected by telluric airglow, and we could not find any rotation period using this index. Further, different definitions of the line indices have no major impact on the results. Comparing the different search methods, the string length method and the phase dispersion minimisation perform worst, while Gaussian process models produce the smallest numbers of false positives and non-detections.

scholarly journals The RS Canum Venaticorum Stars

1992 ◽  
Vol 151 ◽  
pp. 71-82 ◽  
Author(s):  
Marcello Rodonò
Keyword(s):  
Magnetic Fields ◽  
Imaging Techniques ◽  
Zeeman Splitting ◽  
Type Systems ◽  
Spectral Lines ◽  
Stellar Rotation ◽  
Intrinsic Variability ◽  
Temperature Regimes ◽  
Multi Wavelength

The picture emerging from recent studies of RS CVn-type systems indicates the presence of very active stars showing typical solar-like activity phenomena, such as spots and flares, and possibly mutual interactions. The binary nature of RS CVns is certainly important in enforcing high stellar rotation rates, but the actual clue to the understanding of the intrinsic variability of the component stars resides in their internal structure, where the appropriate physical conditions are met for the generation and intensification of strong magnetic fields, as prescribed by the αω-dynamo models. The most significant results have been derived from multi-wavelength, coordinated observations and long-term monitoring programs.Recent highlights include: a) the mapping of compact atmospheric structures at various temperature regimes by light curve modelling and spectral (Doppler) imaging techniques; b) clear evidence of long-term activity cycles on RS CVn and other types of interacting binaries; c) the detection and measurement of surface magnetic fields, as derived from the differential Zeeman splitting of spectral lines.These results clearly demonstrate that the study of RS CVn stars can play a very fundamental role in the understanding of basic stellar physics, as well as in interpreting the characteristic variability of interacting binaries.

scholarly journals Magnetic Fields Measured with the 10830 Å HeI Line

1971 ◽  
Vol 43 ◽  
pp. 279-288 ◽  
Author(s):  
J. Harvey ◽  
D. Hall
Keyword(s):  
Fine Structure ◽  
Magnetic Fields ◽  
Near Infrared ◽  
Active Regions ◽  
Field Measurements ◽  
Spectral Lines ◽  
Magnetic Field Measurements ◽  
Infrared Spectral ◽  
Polarity Reversals ◽  
Absorption Features

Several advantages of near infrared spectral lines for magnetic field measurements are listed. In particular, the 10830 Å multiplet of HeI is well suited for observations of chromospheric magnetic fields.New photoelectric spectroheliograms made with the 10830 Å line reveal a large amount of filamentary fine structure in active regions. This fine structure has important consequences on the interpretation of 10830 Å magnetograms. Except for an association of 10830 Å disk filaments with polarity reversals there is little correlation between absorption features and the 10830 Å longitudinal field. Comparisons of chromospheric and photospheric observations show that the chromospheric field is spatially more diffuse and weaker than the photospheric field.

Magnetohydrodynamics: Overview

2020 ◽  
Author(s):  
E.R. Priest
Keyword(s):  
Magnetic Fields ◽  
Magnetic Energy ◽  
Liquid Metals ◽  
Plasma Heating ◽  
The Sun ◽  
Pressure Gradients ◽  
Dynamo Action ◽  
Electrically Conducting ◽  
Stellar Flares ◽  
Outer Atmosphere

Magnetohydrodynamics is sometimes called magneto-fluid dynamics or hydromagnetics and is referred to as MHD for short. It is the unification of two fields that were completely independent in the 19th, and first half of the 20th, century, namely, electromagnetism and fluid mechanics. It describes the subtle and complex nonlinear interaction between magnetic fields and electrically conducting fluids, which include liquid metals as well as the ionized gases or plasmas that comprise most of the universe. In places such as the Earth’s magnetosphere or the Sun’s outer atmosphere (the corona) where the magnetic field provides an important component of the free energy, MHD effects are responsible for much of the observed dynamic behavior, such as geomagnetic substorms, solar flares and huge eruptions from the Sun that dominate the Earth’s space weather. However, MHD is also of great importance in astrophysics, since many of the MHD processes that are observed in the laboratory or in the Sun and the magnetosphere also take place under different parameter regimes in more exotic cosmical objects such as active stars, accretion discs, and black holes. The different aspects of MHD include determining the nature of: magnetic equilibria under a balance between magnetic forces, pressure gradients and gravity; MHD wave motions; magnetic instabilities; and the important process of magnetic reconnection for converting magnetic energy into other forms. In turn, these aspects play key roles in the fundamental astrophysical processes of magnetoconvection, magnetic flux emergence, star spots, plasma heating, stellar wind acceleration, stellar flares and eruptions, and the generation of magnetic fields by dynamo action.

scholarly journals Magnetic Field Diagnosis Through Spectropolarimetry)

1993 ◽  
Vol 138 ◽  
pp. 232-246 ◽  
Author(s):  
Gautier Mathys
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Longitudinal Magnetic Field ◽  
Quadratic Field ◽  
Spectral Lines ◽  
Stellar Rotation ◽  
The Asymmetry ◽  
The Moment ◽  
Ap Stars ◽  
Original Approach

AbstractAn original approach, the moment technique, is applied to analyze the shapes of spectral lines of Ap stars recorded in both circular polarizations. The longitudinal magnetic field, the asymmetry of the longitudinal magnetic field, and the quadratic field of the studied stars are derived. From the consideration of these quantities and of their variations through the stellar rotation cycle, constraints on the spatially unresolved structure of the magnetic fields are obtained.

scholarly journals HADES RV Programme with HARPS-N at TNG

2019 ◽  
Vol 624 ◽  
pp. A27 ◽  
Author(s):  
E. González-Álvarez ◽  
G. Micela ◽  
J. Maldonado ◽  
L. Affer ◽  
A. Maggio ◽  
...  
Keyword(s):  
Rotation Period ◽  
High Resolution Spectroscopy ◽  
Slow Rotation ◽  
Stellar Rotation ◽  
M Dwarfs ◽  
Dwarf Stars ◽  
Rotation Periods ◽  
Coronal Activity ◽  
Low Mass ◽  
M Dwarf Stars

Aims. We extend the relationship between X-ray luminosity (Lx) and rotation period (Prot) found for main-sequence FGK stars, and test whether it also holds for early M dwarfs, especially in the non-saturated regime (Lx ∝ Prot−2) which corresponds to slow rotators. Methods. We use the luminosity coronal activity indicator (Lx) of a sample of 78 early M dwarfs with masses in the range from 0.3 to 0.75 M⊙ from the HArps-N red Dwarf Exoplanet Survey (HADES) radial velocity (RV) programme collected from ROSAT and XMM-Newton. The determination of the rotation periods (Prot) was done by analysing time series of high-resolution spectroscopy of the Ca II H & K and Hα activity indicators. Our sample principally covers the slow rotation regime with rotation periods from 15 to 60 days. Results. Our work extends to the low mass regime the observed trend for more massive stars showing a continuous shift of the Lx∕Lbol versus Prot power law towards longer rotation period values, and includes a more accurate way to determine the value of the rotation period at which the saturation occurs (Psat) for M dwarf stars. Conclusions. We conclude that the relations between coronal activity and stellar rotation for FGK stars also hold for early M dwarfs in the non-saturated regime, indicating that the rotation period is sufficient to determine the ratio Lx∕Lbol.

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.

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