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 The CARMENES search for exoplanets around M dwarfs

2018 ◽  
Vol 609 ◽  
pp. A117 ◽  
Author(s):  
T. Trifonov ◽  
M. Kürster ◽  
M. Zechmeister ◽  
L. Tal-Or ◽  
J. A. Caballero ◽  
...  
Keyword(s):  
M Dwarfs ◽  
Earth Planet ◽  
Low Mass Stars ◽  
Dwarf Stars ◽  
Orbital Parameters ◽  
Short Period ◽  
Show Evidence ◽  
Bona Fide ◽  
M Dwarf Stars ◽  
Rocky Planets

Context. The main goal of the CARMENES survey is to find Earth-mass planets around nearby M-dwarf stars. Seven M dwarfs included in the CARMENES sample had been observed before with HIRES and HARPS and either were reported to have one short period planetary companion (GJ 15 A, GJ 176, GJ 436, GJ 536 and GJ 1148) or are multiple planetary systems (GJ 581 and GJ 876). Aims. We aim to report new precise optical radial velocity measurements for these planet hosts and test the overall capabilities of CARMENES. Methods. We combined our CARMENES precise Doppler measurements with those available from HIRES and HARPS and derived new orbital parameters for the systems. Bona-fide single planet systems were fitted with a Keplerian model. The multiple planet systems were analyzed using a self-consistent dynamical model and their best fit orbits were tested for long-term stability. Results. We confirm or provide supportive arguments for planets around all the investigated stars except for GJ 15 A, for which we find that the post-discovery HIRES data and our CARMENES data do not show a signal at 11.4 days. Although we cannot confirm the super-Earth planet GJ 15 Ab, we show evidence for a possible long-period (Pc = 7030-630+970 d) Saturn-mass (mcsini = 51.8-5.8+5.5M⊕) planet around GJ 15 A. In addition, based on our CARMENES and HIRES data we discover a second planet around GJ 1148, for which we estimate a period Pc = 532.6-2.5+4.1 days, eccentricity ec = 0.342-0.062+0.050 and minimum mass mcsini = 68.1-2.2+4.9M⊕. Conclusions. The CARMENES optical radial velocities have similar precision and overall scatter when compared to the Doppler measurements conducted with HARPS and HIRES. We conclude that CARMENES is an instrument that is up to the challenge of discovering rocky planets around low-mass stars.

scholarly journals ODUSSEAS: a machine learning tool to derive effective temperature and metallicity for M dwarf stars

2020 ◽  
Vol 636 ◽  
pp. A9 ◽  
Author(s):  
A. Antoniadis-Karnavas ◽  
S. G. Sousa ◽  
E. Delgado-Mena ◽  
N. C. Santos ◽  
G. D. C. Teixeira ◽  
...  
Keyword(s):  
Machine Learning ◽  
Signal To Noise Ratio ◽  
Computational Tool ◽  
M Dwarfs ◽  
Signal To Noise ◽  
Dwarf Stars ◽  
M Dwarf Stars ◽  
M Dwarf ◽  
Python Package ◽  
Machine Learning Tool

Aims. The derivation of spectroscopic parameters for M dwarf stars is very important in the fields of stellar and exoplanet characterization. The goal of this work is the creation of an automatic computational tool able to quickly and reliably derive the Teff and [Fe/H] of M dwarfs using optical spectra obtained by different spectrographs with different resolutions. Methods. ODUSSEAS (Observing Dwarfs Using Stellar Spectroscopic Energy-Absorption Shapes) is based on the measurement of the pseudo equivalent widths for more than 4000 stellar absorption lines and on the use of the machine learning Python package “scikit-learn” for predicting the stellar parameters. Results. We show that our tool is able to derive parameters accurately and with high precision, having precision errors of ~30 K for Teff and ~0.04 dex for [Fe/H]. The results are consistent for spectra with resolutions of between 48 000 and 115 000 and a signal-to-noise ratio above 20.

scholarly journals Photometric flaring fraction of M dwarf stars from the SkyMapper Southern Survey

2019 ◽  
Vol 491 (1) ◽  
pp. 39-50 ◽  
Author(s):  
Seo-Won Chang ◽  
Christian Wolf ◽  
Christopher A Onken
Keyword(s):  
Galactic Plane ◽  
Search Algorithm ◽  
M Dwarfs ◽  
Dwarf Stars ◽  
Vertical Distance ◽  
Steep Decline ◽  
Bona Fide ◽  
Single Epoch ◽  
M Dwarf Stars ◽  
M Dwarf

ABSTRACT We present our search for flares from M dwarf stars in the SkyMapper Southern Survey DR1, which covers nearly the full Southern hemisphere with six-filter sequences that are repeatedly observed in the passbands uvgriz. This allows us to identify bona fide flares in single-epoch observations on time-scales of less than four minutes. Using a correlation-based outlier search algorithm we find 254 flare events in the amplitude range of Δu ∼ 0.1 to 5 mag. In agreement with previous work, we observe the flaring fraction of M dwarfs to increase from ∼30 to ∼1000 per million stars for spectral types M0 to M5. We also confirm the decrease in flare fraction with larger vertical distance from the Galactic plane which is expected from declining stellar activity with age. Based on precise distances from Gaia DR2, we find a steep decline in the flare fraction from the plane to 150 pc vertical distance and a significant flattening towards larger distances. We then reassess the strong type dependence in the flaring fraction with a volume-limited sample within a distance of 50 pc from the Sun: in this sample the trend disappears and we find instead a constant fraction of ∼1 650 per million stars for spectral types M1 to M5. Finally, large-amplitude flares with Δi > 1 mag are very rare with a fraction of ∼0.5 per million M dwarfs. Hence, we expect that M-dwarf flares will not confuse SkyMapper’s search for kilonovae from gravitational-wave events. proper references for those databases (or follow their guideline on citation).

scholarly journals CCD Parallaxes for Southern Very Low Luminosity Stars

1993 ◽  
Vol 156 ◽  
pp. 75-78
Author(s):  
Philip A. Ianna
Keyword(s):  
White Dwarfs ◽  
Late Type ◽  
M Dwarfs ◽  
Dwarf Stars ◽  
Ccd Observations ◽  
Trigonometric Parallaxes ◽  
M Dwarf Stars ◽  
M Dwarf

Trigonometric parallaxes based on CCD observations are presented here for six southern very late-type M dwarf stars and three white dwarfs. The M dwarfs RG0050-2722, ESO207-61, MH2115-4518, MH2124-4228, and LHS3003 are among the very lowest luminosity stars known.

scholarly journals The CARMENES search for exoplanets around M dwarfs

2020 ◽  
Vol 638 ◽  
pp. A115
Author(s):  
D. Hintz ◽  
B. Fuhrmeister ◽  
S. Czesla ◽  
J. H. M. M. Schmitt ◽  
A. Schweitzer ◽  
...  
Keyword(s):  
Radiation Field ◽  
Extreme Ultraviolet ◽  
M Dwarfs ◽  
Dwarf Stars ◽  
Solar Type ◽  
Model Set ◽  
M Dwarf Stars ◽  
First Time ◽  
M Dwarf ◽  
Different Levels

The He I infrared (IR) line at a vacuum wavelength of 10 833 Å is a diagnostic for the investigation of atmospheres of stars and planets orbiting them. For the first time, we study the behavior of the He I IR line in a set of chromospheric models for M-dwarf stars, whose much denser chromospheres may favor collisions for the level population over photoionization and recombination, which are believed to be dominant in solar-type stars. For this purpose, we use published PHOENIX models for stars of spectral types M2 V and M3 V and also compute new series of models with different levels of activity following an ansatz developed for the case of the Sun. We perform a detailed analysis of the behavior of the He I IR line within these models. We evaluate the line in relation to other chromospheric lines and also the influence of the extreme ultraviolet (EUV) radiation field. The analysis of the He I IR line strengths as a function of the respective EUV radiation field strengths suggests that the mechanism of photoionization and recombination is necessary to form the line for inactive models, while collisions start to play a role in our most active models. Moreover, the published model set, which is optimized in the ranges of the Na I D2, Hα, and the bluest Ca II IR triplet line, gives an adequate prediction of the He I IR line for most stars of the stellar sample. Because especially the most inactive stars with weak He I IR lines are fit worst by our models, it seems that our assumption of a 100% filling factor of a single inactive component no longer holds for these stars.

scholarly journals Why do we find ourselves around a yellow star instead of a red star?

2017 ◽  
Vol 17 (1) ◽  
pp. 77-86 ◽  
Author(s):  
Jacob Haqq-Misra ◽  
Ravi Kumar Kopparapu ◽  
Eric T. Wolf
Keyword(s):  
Bayesian Inference ◽  
Habitable Zone ◽  
M Dwarfs ◽  
Dwarf Stars ◽  
Habitable Planets ◽  
Chance Event ◽  
The Future ◽  
M Dwarf Stars ◽  
M Dwarf

AbstractM-dwarf stars are more abundant than G-dwarf stars, so our position as observers on a planet orbiting a G-dwarf raises questions about the suitability of other stellar types for supporting life. If we consider ourselves as typical, in the anthropic sense that our environment is probably a typical one for conscious observers, then we are led to the conclusion that planets orbiting in the habitable zone of G-dwarf stars should be the best place for conscious life to develop. But such a conclusion neglects the possibility that K-dwarfs or M-dwarfs could provide more numerous sites for life to develop, both now and in the future. In this paper we analyse this problem through Bayesian inference to demonstrate that our occurrence around a G-dwarf might be a slight statistical anomaly, but only the sort of chance event that we expect to occur regularly. Even if M-dwarfs provide more numerous habitable planets today and in the future, we still expect mid G- to early K-dwarfs stars to be the most likely place for observers like ourselves. This suggests that observers with similar cognitive capabilities as us are most likely to be found at the present time and place, rather than in the future or around much smaller stars.

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 Detection of an energetic flare from the M5V secondary star in the Polar MQ Dra

2021 ◽  
Author(s):  
Gavin Ramsay ◽  
Pasi Hakala ◽  
Matt A Wood
Keyword(s):  
High Energy ◽  
Dwarf Stars ◽  
Rotation Rates ◽  
Secondary Star ◽  
Rotation Periods ◽  
Profile Characteristic ◽  
M Dwarf Stars ◽  
Mass Ejection ◽  
M Dwarf ◽  
Low Rate

Abstract MQ Dra is a strongly magnetic Cataclysmic Variable whose white dwarf accretes material from its secondary star through a stellar wind at a low rate. TESS observations were made of MQ Dra in four sectors in Cycle 2 and show a short duration, high energy flare (∼1035 erg) which has a profile characteristic of a flare from the M5V secondary star. This is one of the few occasions where an energetic flare has been seen from a Polar. We find no evidence that the flare caused a change in the light curve following the event and consider whether a coronal mass ejection was associated with the flare. We compare the frequency of energetic flares from the secondary star in MQ Dra with M dwarf stars and discuss the overall flare rate of stars with rotation periods shorter than 0.2 d and how such fast rotators can generate magnetic fields with low differential rotation rates.

scholarly journals Differences in radio emission from similar M dwarfs in the binary system Ross 867-8

2020 ◽  
Vol 633 ◽  
pp. A130
Author(s):  
L. H. Quiroga-Nuñez ◽  
H. T. Intema ◽  
J. R. Callingham ◽  
J. Villadsen ◽  
H. J. van Langevelde ◽  
...  
Keyword(s):  
Binary System ◽  
Radio Emission ◽  
Stellar System ◽  
M Dwarfs ◽  
Dwarf Stars ◽  
X Ray ◽  
Peak Flux ◽  
Stellar Properties ◽  
M Dwarf Stars ◽  
M Dwarf

Serendipitously, we rediscovered radio emission from the binary system Ross 867 (M4.5V) and Ross 868 (M3.5V) while inspecting archival Giant Metrewave Radio Telescope (GMRT) observations. The binary system consists of two M-dwarf stars that share common characteristics such as spectral type, astrometric parameters, age, and emission at infrared, optical, and X-ray frequencies. The GMRT data at 610 MHz taken on July 2011 shows that the radio emission from Ross 867 is polarized and highly variable on hour timescales with a peak flux of 10.4 ± 0.7 mJy beam−1. Additionally, after reviewing archival data from several observatories (VLA, GMRT, JVLA, and LOFAR), we confirm that although the two stars are likely coeval, only Ross 867 was detected, while Ross 868 remains undetected at radio wavelengths. As the stars have a large orbital separation, this binary stellar system provides a coeval laboratory to examine and constrain the stellar properties linked to radio activity in M dwarfs. We speculate that the observed difference in radio activity between the dwarfs could be due to vastly different magnetic field topologies or that Ross 867 has an intrinsically different dynamo.

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.

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