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

2018 ◽  
Vol 615 ◽  
pp. A69 ◽  
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.

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 Age, Activity and Rotation in Mid and Late-Type M Dwarfs from MEarth

2013 ◽  
Vol 9 (S302) ◽  
pp. 176-179
Author(s):  
Andrew A. West ◽  
Kolby L. Weisenburger ◽  
Jonathan Irwin ◽  
David Charbonneau ◽  
Jason Dittmann ◽  
...  
Keyword(s):  
Dimensional Space ◽  
Large Fraction ◽  
Rotation Period ◽  
Magnetic Activity ◽  
Rotating Stars ◽  
Late Type ◽  
M Dwarfs ◽  
Magnetic Field Generation ◽  
Rotation Periods ◽  
Wide Range

AbstractUsing spectroscopic observations and photometric light curves of 280 nearby M dwarfs from the MEarth exoplanet transit survey, we examine the relationships between magnetic activity (quantified by Hα emission), rotation period, and stellar age (derived from three-dimensional space velocities). Although we have known for decades that a large fraction of mid-late-type M dwarfs are magnetically active, it was not clear what role rotation played in the magnetic field generation (and subsequent chromospheric heating). Previous attempts to investigate the relationship between magnetic activity and rotation in mid-late-type M dwarfs were hampered by the limited number of M dwarfs with measured rotation periods (and the fact that vsini measurements only probe rapid rotation). However, the photometric data from the MEarth survey allows us to probe a wide range of rotation periods for hundreds of M dwarf stars (from less than one to over 100 days). Over all M spectral types we find that magnetic activity decreases with longer rotation periods, including late-type, fully convective M dwarfs. We find that the most magnetically active (and hence, most rapidly rotating) stars are consistent with a kinematically young population, while slow-rotators are less active or inactive and appear to belong to an older, dynamically heated stellar population.

scholarly journals Revisiting the connection between magnetic activity, rotation period, and convective turnover time for main-sequence stars

2018 ◽  
Vol 618 ◽  
pp. A48 ◽  
Author(s):  
M. Mittag ◽  
J. H. M. M. Schmitt ◽  
K.-P. Schröder
Keyword(s):  
Main Sequence ◽  
Rotation Period ◽  
Magnetic Activity ◽  
Turnover Time ◽  
Rossby Number ◽  
Stellar Rotation ◽  
Main Sequence Stars ◽  
Rotation Periods ◽  
Period Distribution ◽  
Cool Stars

The connection between stellar rotation, stellar activity, and convective turnover time is revisited with a focus on the sole contribution of magnetic activity to the Ca II H&K emission, the so-called excess flux, and its dimensionless indicator R+HK in relation to other stellar parameters and activity indicators. Our study is based on a sample of 169 main-sequence stars with directly measured Mount Wilson S-indices and rotation periods. The R+HK values are derived from the respective S-indices and related to the rotation periods in various B–V-colour intervals. First, we show that stars with vanishing magnetic activity, i.e. stars whose excess flux index R+HK approaches zero, have a well-defined, colour-dependent rotation period distribution; we also show that this rotation period distribution applies to large samples of cool stars for which rotation periods have recently become available. Second, we use empirical arguments to equate this rotation period distribution with the global convective turnover time, which is an approach that allows us to obtain clear relations between the magnetic activity related excess flux index R+HK, rotation periods, and Rossby numbers. Third, we show that the activity versus Rossby number relations are very similar in the different activity indicators. As a consequence of our study, we emphasize that our Rossby number based on the global convective turnover time approaches but does not exceed unity even for entirely inactive stars. Furthermore, the rotation-activity relations might be universal for different activity indicators once the proper scalings are used.

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 HD 965: An extremely peculiar A star with an extremely long rotation period

2019 ◽  
Vol 629 ◽  
pp. A39 ◽  
Author(s):  
G. Mathys ◽  
I. I. Romanyuk ◽  
S. Hubrig ◽  
D. O. Kudryavtsev ◽  
M. Schöller ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Rotation Period ◽  
Field Measurements ◽  
Special Astrophysical Observatory ◽  
General Context ◽  
Rotation Periods ◽  
Variation Curve ◽  
The Mean ◽  
Magnetic Poles ◽  
Ap Stars

Context. One of the keys to understanding the origin of Ap stars and their significance in the general context of stellar astrophysics is by considering the most extreme properties displayed by some of them. For this reason, HD 965 is particularly interesting as it combines some of the most pronounced chemical peculiarities with one of the longest rotation periods known. Aims. We characterise the variations of the magnetic field of the Ap star HD 965 and derive constraints about its structure. Methods. We combined published measurements of the mean longitudinal field ⟨Bz⟩ of HD 965 with new determinations of this field moment from circular spectropolarimetry obtained at the 6-m telescope BTA of the Special Astrophysical Observatory of the Russian Academy of Sciences. For the mean magnetic field modulus ⟨B⟩, literature data were complemented by the analysis of ESO archive spectra. Results. We present the first determination of the rotation period of HD 965, Prot = (16.5 ± 0.5) yr. The star HD 965 is only the third Ap star with a period longer than ten years for which magnetic field measurements have been obtained over more than a full cycle. The variation curve of ⟨Bz⟩ is well approximated by a cosine wave. Furthermore, ⟨B⟩ does not show any significant variation. The observed behaviour of these field moments is well represented by a simple model consisting of the superposition of collinear dipole, quadrupole, and octupole. The distribution of neodymium over the surface of HD 965 is highly non-uniform. The element appears concentrated around the magnetic poles, especially the negative one. Conclusions. The shape of the longitudinal magnetic variation curve of HD 965 indicates that its magnetic field is essentially symmetric about an axis passing through the centre of the star. Overall, HD 965 appears similar to the bulk of the long-period Ap stars, as far as its magnetic field is concerned.

scholarly journals The Rotation of Low-Mass Pre-Main-Sequence Stars

2004 ◽  
Vol 215 ◽  
pp. 113-122 ◽  
Author(s):  
Robert D. Mathieu
Keyword(s):  
Angular Momentum ◽  
Main Sequence ◽  
Rotation Period ◽  
Rotating Stars ◽  
Stellar Rotation ◽  
Main Sequence Stars ◽  
Star Forming ◽  
Rotation Periods ◽  
Order Of Magnitude ◽  
Critical Velocities

Major photometric monitoring campaigns of star-forming regions in the past decade have provided rich rotation period distributions of pre-main-sequence stars. The rotation periods span more than an order of magnitude in period, with most falling between 1 and 10 days. Thus the broad rotation period distributions found in 100 Myr clusters are already established by an age of 1 Myr. The most rapidly rotating stars are within a factor of 2-3 of their critical velocities; if angular momentum is conserved as they evolve to the ZAMS, these stars may come to exceed their critical velocities. Extensive efforts have been made to find connections between stellar rotation and the presence of protostellar disks; at best only a weak correlation has been found in the largest samples. Magnetic disk-locking is a theoretically attractive mechanism for angular momentum evolution of young stars, but the links between theoretical predictions and observational evidence remain ambiguous. Detailed observational and theoretical studies of the magnetospheric environments will provide better insight into the processes of pre-main-sequence stellar angular momentum evolution.

scholarly journals Stellar rotation periods from K2 Campaigns 0–18

2020 ◽  
Vol 635 ◽  
pp. A43 ◽  
Author(s):  
Timo Reinhold ◽  
Saskia Hekker
Keyword(s):  
Gaussian Mixture Models ◽  
Rotation Period ◽  
Gaussian Mixture ◽  
Magnetic Activity ◽  
Stellar Rotation ◽  
Photometric Variability ◽  
Rotation Periods ◽  
Period Distribution ◽  
Brightness Variability ◽  
Stellar Magnetic Activity

Context. Rotation period measurements of stars observed with the Kepler mission have revealed a lack of stars at intermediate rotation periods, accompanied by a decrease of photometric variability. Whether this so-called dearth region is a peculiarity of stars in the Kepler field, or reflects a general manifestation of stellar magnetic activity, is still under debate. The K2 mission has the potential to unravel this mystery by measuring stellar rotation and photometric variability along different fields in the sky. Aims. Our goal is to measure stellar rotation periods and photometric variabilities for tens of thousands of K2 stars, located in different fields along the ecliptic plane, to shed light on the relation between stellar rotation and photometric variability. Methods. We use Lomb–Scargle periodograms, auto-correlation and wavelet functions to determine consistent rotation periods. Stellar brightness variability is assessed by computing the variability range, Rvar, from the light curve. We further apply Gaussian mixture models to search for bimodality in the rotation period distribution. Results. Combining measurements from all K2 campaigns, we detect rotation periods in 29 860 stars. The reliability of these periods was estimated from stars observed more than once. We find that 75–90% of the stars show period deviation smaller than 20% between different campaigns, depending on the peak height threshold in the periodograms. For effective temperatures below 6000 K, the variability range shows a local minimum at different periods, consistent with an isochrone age of ∼750 Myr. Additionally, the rotation period distribution shows evidence for bimodality, although the dearth region in the K2 data is less pronounced compared to the Kepler field. The period at the dip of the bimodal distribution shows good agreement with the period at the local variability minimum. Conclusions. We conclude that the rotation period bimodality is present in different fields of the sky, and is hence a general manifestation of stellar magnetic activity. The reduced variability in the dearth region is interpreted as a cancelation between dark spots and bright faculae. Our results strongly advocate that the role of faculae has been underestimated so far, suggesting a more complex dependence of the brightness variability on the rotation period.

scholarly journals Evidence from stellar rotation for early disc dispersal owing to close companions

2019 ◽  
Vol 627 ◽  
pp. A97
Author(s):  
S. Messina
Keyword(s):  
Rotation Period ◽  
Equal Mass ◽  
Close Binaries ◽  
Stellar Rotation ◽  
Low Mass Stars ◽  
Components Separation ◽  
Rotation Periods ◽  
Period Distribution ◽  
Locking Mechanism ◽  
Average Rotation

Context. Young (≲600 Myr) low-mass stars (M ≲ 1 M⊙) of equal mass exhibit a distribution of rotation periods. At the very early phases of stellar evolution, this distribution is set by the star-disc locking mechanism, which forces stars to rotate at the same rate as the inner edge of the disc. The primordial disc lifetime and consequently the duration of the disc-locking mechanism, can be significantly shortened by the presence of a close companion, making the rotation period distribution of close binaries different from that of either single stars or wide binaries. Aims. We use new data to investigate and better constrain the range of ages, the components separation, and the mass ratio dependence at which the rotation period distribution has been significantly affected by the disc dispersal that is enhanced by close companions. Methods. We select a sample of close binaries in the Upper Scorpius association (age ∼8 Myr) whose components have measured the separation and the rotation periods and compare their period distribution with that of coeval stars that are single stars. Results. We find that components of close binaries have, on average, rotation periods that are shorter than those of single stars. More precisely, binaries with approximately equal-mass components (0.9 ≤ M2/M1 ≤ 1.0) have rotation periods that are shorter than those of single stars by ∼0.4 d on average; the primary and secondary components of binaries with smaller mass ratios (0.8 < M2/M1 < 0.9) have rotation periods that are shorter than those of single stars by ∼1.9 d and ∼1.0 d on average, respectively. A comparison with the older 25 Myr β Pictoris association shows that whereas in the latter, all close binaries with projected separation ρ ≤ 80 AU rotate faster than single stars, in the Upper Scorpius this is only the case for about 70% of stars. Conclusions. We interpret the enhanced rotation in close binaries with respect to single stars as the consequence of an early disc dispersal induced by the presence of close companions. The enhanced rotation suggests that disc dispersal timescales are longest for single stars and shorter for close binaries.

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