scholarly journals Where the Wild Young M Dwarfs Are: the SUPERBLINK Proper Motion Survey and a Search for Low-mass Moving Group Candidates

2015 ◽  
Vol 10 (S314) ◽  
pp. 69-70
Author(s):  
Sébastien Lépine
Keyword(s):  
Local Field ◽  
Proper Motion ◽  
Field Population ◽  
Velocity Space ◽  
Significant Fraction ◽  
Proper Motions ◽  
M Dwarfs ◽  
Low Mass ◽  
Moving Groups ◽  
M Dwarf

AbstractThe SUPERBLINK survey catalogs all stars brighter than R = 19 mag and with proper motions larger than 40 mas yr−1, down to a declination of −33○. The catalog inevitably includes a significant fraction of the presumed low-mass members of several nearby young moving groups (Beta Pic, AB Dor, Tuc-Hor, Argus), or low-mass escapees from the Hyades and Pleiades clusters. We discuss opportunities and challenges in identifying the missing M dwarf members of these moving groups. While rounding up the majority of the potential M dwarf members of these groups, such samples are significantly affected by co-moving field stars, both young and old, due to the heavy clumping of the local field population in velocity space.

Tìm kiếm đĩa tàn dư xung quanh các sao lùn kiểu phổ M-trễ nằm trong vùng lân cận Mặt Trời

2019 ◽  
Vol 15 (9) ◽  
pp. 43
Author(s):  
Nguyễn Thành Đạt ◽  
Phan Bảo Ngọc
Keyword(s):  
Spectral Energy ◽  
Archival Data ◽  
Debris Disks ◽  
M Dwarfs ◽  
Energy Distributions ◽  
Infrared Excess ◽  
Low Mass ◽  
M Dwarf ◽  
Infrared Survey ◽  
Infrared Data

In this paper, we present our search for debris disks in a sample of nearby late-M dwarfs based on infrared data of the Wide Infrared Survey Explorer. Using archival data, we constructed spectral energy distributions of these targets to detect their infrared excess. We detected infrared excess only in one target. This late-M dwarf is an excellent benchmark for further study of disks around very low-mass objects.

scholarly journals Magnetic activity in the HARPS M dwarf sample

2017 ◽  
Vol 600 ◽  
pp. A13 ◽  
Author(s):  
N. Astudillo-Defru ◽  
X. Delfosse ◽  
X. Bonfils ◽  
T. Forveille ◽  
C. Lovis ◽  
...  
Keyword(s):  
Monitoring Program ◽  
Rotation Period ◽  
Magnetic Activity ◽  
Spectral Lines ◽  
M Dwarfs ◽  
Low Mass Stars ◽  
The Galaxy ◽  
Low Mass ◽  
M Dwarf ◽  
The Relationship

Context. Atmospheric magnetic fields in stars with convective envelopes heat stellar chromospheres, and thus increase the observed flux in the Ca ii H and K doublet. Starting with the historical Mount Wilson monitoring program, these two spectral lines have been widely used to trace stellar magnetic activity, and as a proxy for rotation period (Prot) and consequently for stellar age. Monitoring stellar activity has also become essential in filtering out false-positives due to magnetic activity in extra-solar planet surveys. The Ca ii emission is traditionally quantified through the R'HK-index, which compares the chromospheric flux in the doublet to the overall bolometric flux of the star. Much work has been done to characterize this index for FGK-dwarfs, but M dwarfs – the most numerous stars of the Galaxy – were left out of these analyses and no calibration of their Ca ii H and K emission to an R'HK exists to date. Aims. We set out to characterize the magnetic activity of the low- and very-low-mass stars by providing a calibration of the R'HK-index that extends to the realm of M dwarfs, and by evaluating the relationship between R'HK and the rotation period. Methods. We calibrated the bolometric and photospheric factors for M dwarfs to properly transform the S-index (which compares the flux in the Ca ii H and K lines to a close spectral continuum) into the R'HK. We monitored magnetic activity through the Ca ii H and K emission lines in the HARPS M dwarf sample. Results. The R'HK index, like the fractional X-ray luminosity LX/Lbol, shows a saturated correlation with rotation, with saturation setting in around a ten days rotation period. Above that period, slower rotators show weaker Ca ii activity, as expected. Under that period, the R'HK index saturates to approximately 10-4. Stellar mass modulates the Ca ii activity, with R'HK showing a constant basal activity above 0.6 M⊙ and then decreasing with mass between 0.6 M⊙ and the fully-convective limit of 0.35 M⊙. Short-term variability of the activity correlates with its mean level and stars with higher R'HK indexes show larger R'HK variability, as previously observed for earlier spectral types.

scholarly journals Search for Galactic runaway stars using Gaia Data Release 1 and HIPPARCOS proper motions

2018 ◽  
Vol 616 ◽  
pp. A149 ◽  
Author(s):  
J. Maíz Apellániz ◽  
M. Pantaleoni González ◽  
R. H. Barbá ◽  
S. Simón-Díaz ◽  
I. Negueruela ◽  
...  
Keyword(s):  
Proper Motion ◽  
Detection Rate ◽  
Age Effect ◽  
Significant Fraction ◽  
Proper Motions ◽  
The Real ◽  
Data Release ◽  
Supernova Explosions ◽  
Runaway Stars ◽  
Motion Method

Context. The first Gaia Data Release (DR1) significantly improved the previously available proper motions for the majority of the Tycho-2 stars. Aims. We wish to detect runaway stars using Gaia DR1 proper motions and compare our results with previous searches. Methods. Runaway O stars and BA supergiants were detected using a 2D proper motion method. The sample was selected using Simbad, spectra from our GOSSS project, literature spectral types, and photometry processed using the code CHORIZOS. Results. We detect 76 runaway stars, 17 (possibly 19) of them with no prior identification as such, with an estimated detection rate of approximately one half of the real runaway fraction. An age effect appears to be present, with objects of spectral subtype B1 and later having traveled for longer distances than runaways of earlier subtypes. We also tentatively propose that the fraction of runaways is lower among BA supergiants that among O stars, but further studies using future Gaia data releases are needed to confirm this. The frequency of fast rotators is high among runaway O stars, which indicates that a significant fraction of them (and possibly the majority) is produced in supernova explosions.

scholarly journals The EBLM project

2019 ◽  
Vol 626 ◽  
pp. A119 ◽  
Author(s):  
S. Gill ◽  
P. F. L. Maxted ◽  
J. A. Evans ◽  
D. F. Evans ◽  
J. Southworth ◽  
...  
Keyword(s):  
Binary Systems ◽  
Evolutionary Models ◽  
Mixing Length ◽  
M Dwarfs ◽  
Primary Star ◽  
Best Fitting ◽  
Low Mass ◽  
Limb Darkening ◽  
M Dwarf ◽  
Orbital Solution

Some M-dwarfs around F-/G-type stars have been measured to be hotter and larger than predicted by stellar evolution models. Inconsistencies between observations and models need to be addressed with more mass, radius, and luminosity measurements of low-mass stars to test and refine evolutionary models. Our aim is to measure the masses, radii and ages of the stars in five low-mass eclipsing binary systems discovered by the WASP survey. We used WASP photometry to establish eclipse-time ephemerides and to obtain initial estimates for the transit depth and width. Radial velocity measurements were simultaneously fitted with follow-up photometry to find the best-fitting orbital solution. This solution was combined with measurements of atmospheric parameters to interpolate evolutionary models and estimate the mass of the primary star, and the mass and radius of the M-dwarf companion. We assess how the best fitting orbital solution changes if an alternative limb-darkening law is used and quantify the systematic effects of unresolved companions. We also gauge how the best-fitting evolutionary model changes if different values are used for the mixing length parameter and helium enhancement. We report the mass and radius of five M-dwarfs and find little evidence of inflation with respect to evolutionary models. The primary stars in two systems are near the “blue hook” stage of their post sequence evolution, resulting in two possible solutions for mass and age. We find that choices in helium enhancement and mixing-length parameter can introduce an additional 3−5% uncertainty in measured M-dwarf mass. Unresolved companions can introduce an additional 3−8% uncertainty in the radius of an M-dwarf, while the choice of limb-darkening law can introduce up to an additional 2% uncertainty. The choices in orbital fitting and evolutionary models can introduce significant uncertainties in measurements of physical properties of such systems.

scholarly journals 2MASS J15460752−6258042: a mid-M dwarf hosting a prolonged accretion disc

2020 ◽  
Vol 494 (1) ◽  
pp. 62-68 ◽  
Author(s):  
Jinhee Lee ◽  
Inseok Song ◽  
Simon Murphy
Keyword(s):  
Accretion Rate ◽  
Spectral Energy Distribution ◽  
Spectral Energy ◽  
Velocity Measurements ◽  
M Dwarfs ◽  
Low Mass Stars ◽  
Infrared Excess ◽  
Low Mass ◽  
M Dwarf ◽  
Gaia Dr2

ABSTRACT We report the discovery of the oldest (∼55 Myr) mid-M type star known to host ongoing accretion. 2MASS J15460752–6258042 (2M1546, spectral type M5, 59.2 pc) shows spectroscopic signs of accretion such as strong H α, He i, and [O i] emission lines, from which we estimate an accretion rate of ∼10−10 M⊙ yr−1. Considering the clearly detected infrared excess in all WISE bands, the shape of its spectral energy distribution (SED) and its age, we believe that the star is surrounded by a transitional disc, clearly with some gas still present at inner radii. The position and kinematics of the star from Gaia DR2 and our own radial-velocity measurements suggest membership in the nearby ∼55 Myr-old Argus moving group. At only 59 pc from Earth, 2M1546 is one of the nearest accreting mid-M dwarfs, making it an ideal target for studying the upper limit on the lifetimes of gas-rich discs around low-mass stars.

scholarly journals Toward Direct Imaging of Low-mass Gas-Giant Planets with the James Webb Space Telescope

2015 ◽  
Vol 10 (S314) ◽  
pp. 288-289 ◽  
Author(s):  
J. E. Schlieder ◽  
C. A. Beichman ◽  
M. R. Meyer ◽  
T. Greene
Keyword(s):  
M Dwarfs ◽  
Direct Imaging ◽  
New Members ◽  
Space Telescope ◽  
James Webb Space Telescope ◽  
Low Mass ◽  
Gas Giant ◽  
Near Term ◽  
Current Sample ◽  
M Dwarf

AbstractIn preparation for observations with the James Webb Space Telescope (JWST), we have identified new members of the nearby, young M dwarf sample and compiled an up to date list of these stars. Here we summarize our efforts to identify young M dwarfs, describe the current sample, and detail its demographics in the context of direct planet imaging. We also describe our investigations of the unprecedented sensitivity of the JWST when imaging nearby, young M dwarfs. The JWST is the only near term facility capable of routinely pushing direct imaging capabilities around M dwarfs to sub-Jovian masses and will provide key insight into questions regarding low-mass gas-giant properties, frequency, formation, and architectures.

scholarly journals New disk discovered with VLT/SPHERE around the M star GSC 07396−00759

2018 ◽  
Vol 613 ◽  
pp. L6 ◽  
Author(s):  
E. Sissa ◽  
J. Olofsson ◽  
A. Vigan ◽  
J. C. Augereau ◽  
V. D’Orazi ◽  
...  
Keyword(s):  
Near Infrared ◽  
Scattered Light ◽  
Debris Disks ◽  
M Dwarfs ◽  
Infrared Excess ◽  
Asymmetric Structures ◽  
High Resolution Imagery ◽  
Low Mass ◽  
Dust Dynamics ◽  
M Dwarf

Debris disks are usually detected through the infrared excess over the photospheric level of their host star. The most favorable stars for disk detection are those with spectral types between A and K, while the statistics for debris disks detected around low-mass M-type stars is very low, either because they are rare or because they are more difficult to detect. Terrestrial planets, on the other hand, may be common around M-type stars. Here, we report on the discovery of an extended (likely) debris disk around the M-dwarf GSC 07396−00759. The star is a wide companion of the close accreting binary V4046 Sgr. The system probably is a member of the β Pictoris Moving Group. We resolve the disk in scattered light, exploiting high-contrast, high-resolution imagery with the two near-infrared subsystems of the VLT/SPHERE instrument, operating in the Y J bands and the H2H3 doublet. The disk is clearly detected up to 1.5′′ (~110 au) from the star and appears as a ring, with an inclination i ~ 83°, and a peak density position at ~70 au. The spatial extension of the disk suggests that the dust dynamics is affected by a strong stellar wind, showing similarities with the AU Mic system that has also been resolved with SPHERE. The images show faint asymmetric structures at the widest separation in the northwest side. We also set an upper limit for the presence of giant planets to 2 MJ. Finally, we note that the 2 resolved disks around M-type stars of 30 such stars observed with SPHERE are viewed close to edge-on, suggesting that a significant population of debris disks around M dwarfs could remain undetected because of an unfavorable orientation.

scholarly journals New ultracool dwarf neighbours within 20 pc from Gaia DR2

2020 ◽  
Vol 637 ◽  
pp. A45
Author(s):  
R.-D. Scholz
Keyword(s):  
Proper Motion ◽  
Visual Inspection ◽  
Near Infrared ◽  
Galactic Plane ◽  
Proper Motions ◽  
Magnitude Diagram ◽  
Motion Measurements ◽  
Moving Groups ◽  
Absolute Magnitudes ◽  
Gaia Dr2

Aims. The Gaia data release 2 (DR2) contains > 6000 objects with parallaxes (Plx + 3 × e_Plx) > 50 mas, placing them within 20 pc from the Sun. Because the expected numbers based on extrapolating the well-known 10 pc census are much lower, nearby Gaia stars need a quality assessment. The 20 pc sample of white dwarfs (WDs) has been verified and completed with Gaia DR2. We here confirm and complete the 20 pc sample of ultracool dwarfs (UCDs) with spectral types ≳M7 and given Gaia DR2 parallaxes. Methods. Dividing the Gaia DR2 20 pc sample into subsamples of various astrometric and photometric quality, we studied their distribution on the sky, in the MG versus G − RP colour-magnitude diagram (CMD), and as a function of G magnitude and total proper motion. After excluding 139 known WDs and 263 known UCDs from the CMD, we checked all remaining ≈3500 candidates with MG >  14 mag (used to define UCDs in this study) for the correctness of their Gaia DR2 proper motions by visual inspection of finder charts, comparison with proper motion catalogues, and comparison with our own proper motion measurements. For confirmed UCD candidates we estimated spectral types photometrically using Gaia and near-infrared absolute magnitudes and colours. Results. We failed to confirm new WDs, but found 50 new UCD candidates that are not mentioned in three previous studies using Gaia DR2. They have relatively small proper motions and low tangential velocities and are concentrated towards the Galactic plane. Half of them have spectral types in SIMBAD and/or previous non-Gaia distance estimates that placed them already within 20 pc. For 20 of the 50 objects, we estimated photometric spectral types of M6−M6.5, slightly below the classical UCD spectral type limit. However, seven L4.5−L6.5, four L0−L1, five M8.5−M9.5, and three M7−M8 dwarfs can be considered as completely new UCDs discoveries within 20 pc based on Gaia DR2. Four M6.5 and two L4.5 dwarfs have high membership probabilities (64%−99%) in the ARGUS, AB Doradus, or Carina Near young moving groups.

scholarly journals The substructure of the Perseus star-forming region: a survey with Gaia DR2

2021 ◽  
Vol 503 (3) ◽  
pp. 3232-3242
Author(s):  
Tatiana Pavlidou ◽  
Aleks Scholz ◽  
Paula S Teixeira
Keyword(s):  
Proper Motion ◽  
Motion Parallax ◽  
Young Stars ◽  
Galactic Latitude ◽  
Proper Motions ◽  
Kinematic Data ◽  
Star Forming ◽  
Moving Groups ◽  
Cold Dust ◽  
Gaia Dr2

ABSTRACT We use photometric and kinematic data from Gaia DR2 to explore the structure of the star-forming region associated with the molecular cloud of Perseus. Apart from the two well-known clusters, IC 348 and NGC 1333, we present five new clustered groups of young stars, which contain between 30 and 300 members, named Autochthe, Alcaeus, Heleus, Electryon, and Mestor. We demonstrate that these are co-moving groups of young stars, based on how the candidate members are distributed in position, proper motion, parallax, and colour–magnitude space. By comparing their colour–magnitude diagrams to isochrones, we show that they have ages between 1 and 5 Myr. Using 2MASS and WISE colours, we find that the fraction of stars with discs in each group ranges from 10 to ∼50 per cent. The youngest of the new groups is also associated with a reservoir of cold dust, according to the Planck map at 353 GHz. We compare the ages and proper motions of the five new groups to those of IC 348 and NGC 1333. Autochthe is clearly linked with NGC 1333 and may have formed in the same star formation event. The seven groups separate roughly into two sets that share proper motion, parallax, and age: Heleus, Electryon, and Mestor as the older set, and NGC 1333 and Autochthe as the younger set. Alcaeus is kinematically related to the younger set, but at a more advanced age, while the properties of IC 348 overlap with both sets. All older groups in this star-forming region are located at higher galactic latitude.

scholarly journals Dynamical masses of M-dwarf binaries in young moving groups

2018 ◽  
Vol 618 ◽  
pp. A23 ◽  
Author(s):  
L. Rodet ◽  
M. Bonnefoy ◽  
S. Durkan ◽  
H. Beust ◽  
A.-M. Lagrange ◽  
...  
Keyword(s):  
Spectral Type ◽  
Total Mass ◽  
Mass Measurement ◽  
Evolutionary Models ◽  
Dynamical Mass ◽  
Low Mass ◽  
Moving Groups ◽  
The Individual ◽  
M Dwarf ◽  
Dynamical Masses

Context. Evolutionary models are widely used to infer the mass of stars, brown dwarfs, and giant planets. Their predictions are thought to be less reliable at young ages (< 200 Myr) and in the low-mass regime (< 1 M⊙). GJ 2060 AB and TWA 22 AB are two rare astrometric M-dwarf binaries, respectively members of the AB Doradus (AB Dor) and Beta Pictoris (β Pic) moving groups. As their dynamical mass can be measured to within a few years, they can be used to calibrate the evolutionary tracks and set new constraints on the age of young moving groups. Aims. We provide the first dynamical mass measurement of GJ 2060 and a refined measurement of the total mass of TWA 22. We also characterize the atmospheric properties of the individual components of GJ 2060 that can be used as inputs to the evolutionary models. Methods. We used NaCo and SPHERE observations at VLT and archival Keck/NIRC2 data to complement the astrometric monitoring of the binaries. We combined the astrometry with new HARPS radial velocities (RVs) and FEROS RVs of GJ 2060. We used a Markov chain Monte-Carlo (MCMC) module to estimate posteriors on the orbital parameters and dynamical masses of GJ 2060 AB and TWA 22 AB from the astrometry and RVs. Complementary data obtained with the integral field spectrograph VLT/SINFONI were gathered to extract the individual near-infrared (1.1–2.5 μm) medium-resolution (R ∼ 1500 − 2000) spectra of GJ 2060 A and B. We compared the spectra to those of known objects and to grids of BT-SETTL model spectra to infer the spectral type, bolometric luminosities, and temperatures of those objects. Results. We find a total mass of 0.18 ± 0.02 M⊙ for TWA 22, which is in good agreement with model predictions at the age of the β Pic moving group. We obtain a total mass of 1.09 ± 0.10 M⊙ for GJ 2060. We estimate a spectral type of M1 ± 0.5, L/L⊙ = −1.20 ± 0.05 dex, and Teff = 3700 ± 100 K for GJ 2060 A. The B component is a M3 ± 0.5 dwarf with L/L⊙ = −1.63 ± 0.05 dex and Teff = 3400 ± 100 K. The dynamical mass of GJ 2060 AB is inconsistent with the most recent models predictions (BCAH15, PARSEC) for an AB Dor age in the range 50–150 Myr. It is 10%–20% (1–2σ, depending on the assumed age) above the model’s predictions, corresponding to an underestimation of 0.10–0.20 M⊙. Coevality suggests a young age for the system (∼50 Myr) according to most evolutionary models. Conclusions. TWA 22 validates the predictions of recent evolutionary tracks at ∼20 Myr. On the other hand, we evidence a 1–2σ mismatch between the predicted and observed mass of GJ 2060 AB. This slight departure may indicate that one of the stars hosts a tight companion. Alternatively, this would confirm the model’s tendency to underestimate the mass of young low-mass stars.

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