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 Planet formation around M dwarfs via disc instability

2020 ◽  
Vol 633 ◽  
pp. A116
Author(s):  
Anthony Mercer ◽  
Dimitris Stamatellos
Keyword(s):  
Planet Formation ◽  
M Dwarfs ◽  
Low Mass Stars ◽  
Dwarf Stars ◽  
Low Mass ◽  
Protostellar Discs ◽  
Stellar Masses ◽  
M Dwarf Stars ◽  
Core Accretion ◽  
M Dwarf

Context. Around 30 per cent of the observed exoplanets that orbit M dwarf stars are gas giants that are more massive than Jupiter. These planets are prime candidates for formation by disc instability. Aims. We want to determine the conditions for disc fragmentation around M dwarfs and the properties of the planets that are formed by disc instability. Methods. We performed hydrodynamic simulations of M dwarf protostellar discs in order to determine the minimum disc mass required for gravitational fragmentation to occur. Different stellar masses, disc radii, and metallicities were considered. The mass of each protostellar disc was steadily increased until the disc fragmented and a protoplanet was formed. Results. We find that a disc-to-star mass ratio between ~0.3 and ~0.6 is required for fragmentation to happen. The minimum mass at which a disc fragment increases with the stellar mass and the disc size. Metallicity does not significantly affect the minimum disc fragmentation mass but high metallicity may suppress fragmentation. Protoplanets form quickly (within a few thousand years) at distances around ~50 AU from the host star, and they are initially very hot; their centres have temperatures similar to the ones expected at the accretion shocks around planets formed by core accretion (up to 12 000 K). The final properties of these planets (e.g. mass and orbital radius) are determined through long-term disc-planet or planet–planet interactions. Conclusions. Disc instability is a plausible way to form gas giant planets around M dwarfs provided that discs have at least 30% the mass of their host stars during the initial stages of their formation. Future observations of massive M dwarf discs or planets around very young M dwarfs are required to establish the importance of disc instability for planet formation around low-mass stars.

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 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 The CARMENES search for exoplanets around M dwarfs

2018 ◽  
Vol 619 ◽  
pp. A32 ◽  
Author(s):  
D. Baroch ◽  
J. C. Morales ◽  
I. Ribas ◽  
L. Tal-Or ◽  
M. Zechmeister ◽  
...  
Keyword(s):  
Binary Systems ◽  
Spectroscopic Binaries ◽  
M Dwarfs ◽  
Dwarf Stars ◽  
Double Line ◽  
Orbital Parameters ◽  
Rotation Periods ◽  
Spectroscopic Binary ◽  
M Dwarf Stars ◽  
M Dwarf

Context. The CARMENES spectrograph is surveying ∼300 M dwarf stars in search for exoplanets. Among the target stars, spectroscopic binary systems have been discovered, which can be used to measure fundamental properties of stars. Aims. Using spectroscopic observations, we determine the orbital and physical properties of nine new double-line spectroscopic binary systems by analysing their radial velocity curves. Methods. We use two-dimensional cross-correlation techniques to derive the radial velocities of the targets, which are then employed to determine the orbital properties. Photometric data from the literature are also analysed to search for possible eclipses and to measure stellar variability, which can yield rotation periods. Results. Out of the 342 stars selected for the CARMENES survey, 9 have been found to be double-line spectroscopic binaries, with periods ranging from 1.13 to ∼8000 days and orbits with eccentricities up to 0.54. We provide empirical orbital properties and minimum masses for the sample of spectroscopic binaries. Absolute masses are also estimated from mass-luminosity calibrations, ranging between ∼0.1 and ∼0.6 M⊙. Conclusions. These new binary systems increase the number of double-line M dwarf binary systems with known orbital parameters by 15%, and they have lower mass ratios on average.

scholarly journals Activity and differential rotation of the early M dwarf Kepler-45 from transit mapping

2020 ◽  
Vol 492 (4) ◽  
pp. 5141-5151
Author(s):  
S M Zaleski ◽  
A Valio ◽  
B D Carter ◽  
S C Marsden
Keyword(s):  
Differential Rotation ◽  
Rotation Period ◽  
Activity Cycle ◽  
Theoretical Modelling ◽  
Stellar Rotation ◽  
M Dwarfs ◽  
Convective Envelope ◽  
Rotation Periods ◽  
Solar Type ◽  
Rotational Shear

ABSTRACT Little is known of the activity and differential rotation of low luminosity, early M dwarfs from direct observation. We present the first stellar activity analysis of star-spots and faculae for the hot Jupiter hosting M1V dwarf Kepler-45 from $\it Kepler$ transit light curves. We find star-spot and facula temperatures contrasting a few hundred degrees with the quiet photosphere, hence similar to other early M dwarfs having a convective envelope surrounding a radiative core. Star-spots are prominent close to the centre of the stellar disc, with faculae prominent towards the limbs, similar to what is observed for the Sun. Star-spot and facula mean sizes are about 40 and 45 × 103 km, respectively, and thus faculae occupy a 10 per cent larger surface area than the star-spots. A short-term activity cycle of about 295 d is observed that is reminiscent of those seen for other cool dwarfs. Adopting a solar-type differential rotation profile (faster equatorial rotation than polar rotation), our star-spot and facula temporal mapping indicates a rotation period of 15.520 ± 0.025 d at the transit latitude of −33.2°. From the mean stellar rotation of 15.762 d, we estimate a rotational shear of 0.031 ± 0.004 rad d−1, or a relative differential rotation of 7.8 ± 0.9 per cent. Kepler-45’s surface rotational shear is thus consistent with observations and theoretical modelling of other early M dwarfs that indicate a shear of less than 0.045 rad d−1 and no less than 0.03 rad d−1 for stars with similar stellar rotation periods.

scholarly journals Activity-Induced Radial Velocity Variation of M Dwarf Stars

2012 ◽  
Vol 8 (S293) ◽  
pp. 197-200
Author(s):  
Jan Marie Andersen ◽  
Heidi Korhonen
Keyword(s):  
Radial Velocity ◽  
Magnetic Activity ◽  
Velocity Variation ◽  
M Dwarfs ◽  
Dwarf Stars ◽  
Highly Active ◽  
Radial Velocity Variation ◽  
Low Mass ◽  
M Dwarf Stars ◽  
M Dwarf

AbstractStellar magnetic activity manifests itself in a variety of ways including starspots–cool, dark regions on the stellar surface. Starspots can cause variations (‘jitter’) in spectral line-profiles which can mimic the radial velocity (RV) variations caused by an orbiting planet, or create RV noise that can drown out a planetary signature. Cool, low-mass M dwarf stars can be highly active, which can make detection of potentially habitable planets around these stars difficult. We investigate radial velocity variations caused by different activity (spot) patterns on M dwarf stars in order to determine the limits of detectability for small planets orbiting active M dwarfs. We report on our progress toward the aim of answering the following questions: What types of spot patterns are realistic for M dwarf stars? What effect will spots have on M dwarf RV measurements? Can jitter from M dwarf spots mimic planetary signals? What is the ideal observing wavelength to reduce M dwarf jitter?

scholarly journals HADES RV programme with HARPS-N at TNG

2020 ◽  
Vol 644 ◽  
pp. A68
Author(s):  
J. Maldonado ◽  
G. Micela ◽  
M. Baratella ◽  
V. D’Orazi ◽  
L. Affer ◽  
...  
Keyword(s):  
High Resolution ◽  
Stellar Mass ◽  
M Dwarfs ◽  
Dwarf Stars ◽  
Large Sample ◽  
Abundance Trends ◽  
Low Mass ◽  
M Dwarf Stars ◽  
First Time ◽  
M Dwarf

Context. Most of our current knowledge on planet formation is still based on the analysis of main sequence, solar-type stars. Conversely, detailed chemical studies of large samples of M dwarfs hosting planets are still missing. Aims. Correlations exist between the presence of different types of planets around FGK stars and metallicity, individual chemical abundance, and stellar mass. We aim to test whether or not these correlations still hold for the less-massive M dwarf stars. Methods to determine stellar abundances of M dwarfs from high-resolution optical spectra in a consistent way are still missing. The present work is a first attempt to fill this gap. Methods. We analyse a large sample of M dwarfs with and without known planetary companions in a coherent and homogeneous way. We develop for the first time a methodology to determine stellar abundances of elements other than iron for M dwarf stars from high-resolution optical spectra. Our methodology is based on the use of a principal component analysis and sparse Bayesian methods. We made use of a set of M dwarfs orbiting around an FGK primary with known abundances to train our methods. We applied our methods to derive stellar metalliticies and abundances of a large sample of M dwarfs observed within the framework of current radial-velocity surveys. We then used a sample of nearby FGK stars to cross-validate our technique by comparing the derived abundance trends in the M dwarf sample with those found on the FGK stars. Results. The metallicity distribution of the different subsamples reveals a correlation between the metallicities of M dwarfs and their probability of hosting giant planets. We also find a correlation between this latter probability and stellar mass. M dwarfs hosting low-mass planets do not seem to follow the so-called planet–metallicity correlation. We also find that the frequency of low-mass planets does not depend on the mass of the stellar host. These results appear to be in agreement with those of previous works. However, we note that for giant-planet hosts our metallicities predict a weaker planet–host metallicity correlation but a stronger mass-dependency than corresponding values derived from photometric results. We show for the first time that there seems to be no differences between M dwarfs with and without known planets in terms of their abundance distributions of elements different from iron. Conclusions. Our data show that low-mass stars with planets follow the same metallicity, mass, and abundance trends as their FGK counterparts, which are usually explained within the framework of core-accretion models.

scholarly journals Multi-Wavelength High-Resolution Spectroscopy for Exoplanet Detection: Motivation, Instrumentation and First Results

Geosciences ◽  
2018 ◽  
Vol 8 (8) ◽  
pp. 289 ◽  
Author(s):  
Serena Benatti
Keyword(s):  
High Resolution ◽  
Near Infrared ◽  
Giant Planet ◽  
High Resolution Spectroscopy ◽  
M Dwarfs ◽  
Low Mass Stars ◽  
First Results ◽  
Multi Wavelength ◽  
Low Mass ◽  
Rocky Planets

Exoplanet research has shown an incessant growth since the first claim of a hot giant planet around a solar-like star in the mid-1990s. Today, the new facilities are working to spot the first habitable rocky planets around low-mass stars as a forerunner for the detection of the long-awaited Sun-Earth analog system. All the achievements in this field would not have been possible without the constant development of the technology and of new methods to detect more and more challenging planets. After the consolidation of a top-level instrumentation for high-resolution spectroscopy in the visible wavelength range, a huge effort is now dedicated to reaching the same precision and accuracy in the near-infrared. Actually, observations in this range present several advantages in the search for exoplanets around M dwarfs, known to be the most favorable targets to detect possible habitable planets. They are also characterized by intense stellar activity, which hampers planet detection, but its impact on the radial velocity modulation is mitigated in the infrared. Simultaneous observations in the visible and near-infrared ranges appear to be an even more powerful technique since they provide combined and complementary information, also useful for many other exoplanetary science cases.

scholarly journals The CARMENES search for exoplanets around M dwarfs

2020 ◽  
Vol 640 ◽  
pp. A52
Author(s):  
B. Fuhrmeister ◽  
S. Czesla ◽  
L. Hildebrandt ◽  
E. Nagel ◽  
J. H. M. M. Schmitt ◽  
...  
Keyword(s):  
Near Infrared ◽  
Extreme Ultraviolet ◽  
High Energy ◽  
M Dwarfs ◽  
Dwarf Stars ◽  
Transmission Spectroscopy ◽  
Solar Type ◽  
Energy Irradiation ◽  
Planetary Transmission ◽  
M Dwarf Stars

The He I infrared (IR) triplet at 10 830 Å is known as an activity indicator in solar-type stars and has become a primary diagnostic in exoplanetary transmission spectroscopy. He I IR lines are a tracer of the stellar extreme-ultraviolet irradiation from the transition region and corona. We study the variability of the He I triplet lines in a spectral time series of 319 M dwarf stars that was obtained with the CARMENES high-resolution optical and near-infrared spectrograph at Calar Alto. We detect He I IR line variability in 18% of our sample stars, all of which show Hα in emission. Therefore, we find detectable He I variability in 78% of the sub-sample of stars with Hα emission. Detectable variability is strongly concentrated in the latest spectral sub-types, where the He I lines during quiescence are typically weak. The fraction of stars with detectable He I variation remains lower than 10% for stars earlier than M3.0 V, while it exceeds 30% for the later spectral sub-types. Flares are accompanied by particularly pronounced line variations, including strongly broadened lines with red and blue asymmetries. However, we also find evidence for enhanced He I absorption, which is potentially associated with increased high-energy irradiation levels at flare onset. Generally, He I and Hα line variations tend to be correlated, with Hα being the most sensitive indicator in terms of pseudo-equivalent width variation. This makes the He I triplet a favourable target for planetary transmission spectroscopy.

scholarly journals Molecular Opacities in Cool Dwarf Stars

1994 ◽  
Vol 146 ◽  
pp. 61-70
Author(s):  
James Liebert
Keyword(s):  
Main Sequence ◽  
Galactic Disk ◽  
Small Radius ◽  
The Sun ◽  
M Dwarfs ◽  
Hydrogen Burning ◽  
Dwarf Stars ◽  
Low Mass ◽  
High Space ◽  
Lower Luminosity

The term dwarf stars identifies objects of small radius in the Hertzsprung-Russell (H-R) Diagram, but encompasses more than one phase of stellar evolution. The M dwarfs (type dM) populate the main sequence at the low mass end; these are the coolest core hydrogen-burning stars. They belong generally to the Galactic disk, or Population I, have relatively small space motions with respect to the Sun, and have similar metallicities to the Sun (although perhaps only within a factor of several). In particular, this means that the abundance of oxygen is always greater than that of carbon. The M subdwarfs (sdM) are the Population II counterparts, showing low metallicities and high space motions. Because they have smaller radii, they define a main sequence at lower luminosity than the M dwarfs for a given temperature. Hence the term subdwarf.

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