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 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 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 Early science with the Large Millimetre Telescope: new mm-wave detections of circumstellar discs in IC 348 from LMT/AzTEC

2019 ◽  
Vol 488 (1) ◽  
pp. 1462-1480
Author(s):  
Michael S Petersen ◽  
Robert A Gutermuth ◽  
Erick Nagel ◽  
Grant W Wilson ◽  
James Lane
Keyword(s):  
Sensitive Indicator ◽  
High Mass ◽  
Spectral Energy ◽  
Complete Sample ◽  
Energy Distributions ◽  
Infrared Excess ◽  
Star Forming ◽  
Star Forming Regions ◽  
Low Mass ◽  
Stellar Properties

Abstract We present the most complete sample of mm measurements of protoplanetary discs in the star-forming region IC 348 to date. New observations from the Large Millimetre Telescope and the 1.1 mm camera AzTEC are combined with literature results in order to characterize the disc population as relating to both stellar properties within the IC 348 region and across other star-forming regions. In addition to detecting 28 of 116 observed known infrared-excess sources, we detected emission from two previously unknown candidate transition discs in the region. When combined with literature results, we find evidence for a steeper-than-expected slope, on average, in disc spectral energy distributions at millimetre wavelengths in the IC 348 region. We show that the presence or absence of high-mass discs is a sensitive indicator of regional evolution, both among star-forming regions and within IC 348. In contrast, low-mass discs exhibit almost no apparent evolution within the first ∼5 Myr when compared among regions.

scholarly journals Characterization of M dwarfs using optical mid-resolution spectra for exploration of small exoplanets

2020 ◽  
Author(s):  
Yohei Koizumi ◽  
Masayuki Kuzuhara ◽  
Masashi Omiya ◽  
Teruyuki Hirano ◽  
John Wisniewski ◽  
...  
Keyword(s):  
Sample Selection ◽  
Optical Spectra ◽  
Average Error ◽  
Spectral Energy ◽  
M Dwarfs ◽  
Energy Distributions ◽  
Fitting Procedures ◽  
Optical Region ◽  
Selection For

Abstract We present the optical spectra of 338 nearby M dwarfs, and compute their spectral types, effective temperatures (Teff), and radii. Our spectra were obtained using several optical spectrometers with spectral resolutions that range from 1200 to 10000. As many as 97% of the observed M-type dwarfs have a spectral type of M3–M6, with a typical error of 0.4 subtype, among which the spectral types M4–M5 are the most common. We infer the Teff of our sample by fitting our spectra with theoretical spectra from the PHOENIX model. Our inferred Teff is calibrated with the optical spectra of M dwarfs whose Teff have been well determined with the calibrations that are supported by previous interferometric observations. Our fitting procedures utilize the VO absorption band (7320–7570 Å) and the optical region (5000–8000 Å), yielding typical errors of 128 K (VO band) and 85 K (optical region). We also determine the radii of our sample from their spectral energy distributions. We find most of our sample stars have radii of <0.6 R⊙, with the average error being 3%. Our catalog enables efficient sample selection for exoplanet surveys around nearby M-type dwarfs.

scholarly journals Sporadic and intense accretion in a 1 Myr-old brown dwarf candidate

2020 ◽  
Vol 634 ◽  
pp. A128
Author(s):  
D. Nguyen-Thanh ◽  
N. Phan-Bao ◽  
S. J. Murphy ◽  
M. S. Bessell
Keyword(s):  
Spectral Energy Distribution ◽  
Brown Dwarfs ◽  
Photometric Data ◽  
Spectral Energy ◽  
Brown Dwarf ◽  
M Dwarfs ◽  
Trigonometric Parallax ◽  
Accretion Process ◽  
Accretion Rates ◽  
Low Mass

Context. Studying the accretion process in very low-mass objects has important implications for understanding their formation mechanism. Many nearby late-M dwarfs that have previously been identified in the field are in fact young brown dwarf members of nearby young associations. Some of them are still accreting. They are therefore excellent targets for further studies of the accretion process in the very low-mass regime at different stages. Aims. We aim to search for accreting young brown dwarf candidates in a sample of 85 nearby late-M dwarfs. Methods. Using photometric data from DENIS, 2MASS, and WISE, we constructed the spectral energy distribution of the late- M dwarfs based on BT-Settl models to detect infrared excesses. We then searched for lithium and Hα emission in candidates that exhibit infrared excesses to confirm their youth and the presence of accretion. Results. Among the 85 late-M dwarfs, only DENIS-P J1538317−103850 (M5.5) shows strong infrared excesses in WISE bands. The detection of lithium absorption in the M5.5 dwarf and its Gaia trigonometric parallax indicate an age of ~1 Myr and a mass of 47 MJ. The Hα emission line in the brown dwarf shows significant variability that indicates sporadic accretion. This 1 Myr-old brown dwarf also exhibits intense accretion bursts with accretion rates of up to 10−7.9 M⊙ yr−1. Conclusions. Our detection of sporadic accretion in one of the youngest brown dwarfs might imply that sporadic accretion at early stages could play an important role in the formation of brown dwarfs. Very low-mass cores would not be able to accrete enough material to become stars, and thus they end up as brown dwarfs.

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 Mon-735: a new low-mass pre-main-sequence eclipsing binary in NGC 2264

2020 ◽  
Vol 495 (2) ◽  
pp. 1531-1548
Author(s):  
Edward Gillen ◽  
Lynne A Hillenbrand ◽  
John Stauffer ◽  
Suzanne Aigrain ◽  
Luisa Rebull ◽  
...  
Keyword(s):  
Main Sequence ◽  
Spectral Energy Distribution ◽  
Spectral Energy ◽  
Centre Of Mass ◽  
M Dwarfs ◽  
Eclipsing Binary ◽  
Star Forming ◽  
Low Mass ◽  
Effective Temperatures

ABSTRACT We present Mon-735, a detached double-lined eclipsing binary (EB) member of the ∼3 Myr old NGC 2264 star-forming region, detected by Spitzer. We simultaneously model the Spitzer light curves, follow-up Keck/HIRES radial velocities, and the system’s spectral energy distribution to determine self-consistent masses, radii, and effective temperatures for both stars. We find that Mon-735 comprises two pre-main-sequence M dwarfs with component masses of M = 0.2918 ± 0.0099 and 0.2661 ± 0.0095 M⊙, radii of R = 0.762 ± 0.022 and 0.748 ± 0.023 R⊙, and effective temperatures of Teff = 3260 ± 73 and 3213 ± 73 K. The two stars travel on circular orbits around their common centre of mass in P = 1.9751388 ± 0.0000050 d. We compare our results for Mon-735, along with another EB in NGC 2264 (CoRoT 223992193), to the predictions of five stellar evolution models. These suggest that the lower mass EB system Mon-735 is older than CoRoT 223992193 in the mass–radius diagram (MRD) and, to a lesser extent, in the Hertzsprung–Russell diagram (HRD). The MRD ages of Mon-735 and CoRoT 223992193 are ∼7–9 and 4–6 Myr, respectively, with the two components in each EB system possessing consistent ages.

scholarly journals CARMENES input catalogue of M dwarfs

2020 ◽  
Vol 642 ◽  
pp. A115 ◽  
Author(s):  
C. Cifuentes ◽  
J. A. Caballero ◽  
M. Cortés-Contreras ◽  
D. Montes ◽  
F. J. Abellán ◽  
...  
Keyword(s):  
Parameter Determination ◽  
Spectral Energy ◽  
M Dwarfs ◽  
Energy Distributions ◽  
Multiple Systems ◽  
New Era ◽  
Virtual Observatory Tools ◽  
Absolute Magnitudes ◽  
The Impact ◽  
Input Catalogue

Context. The relevance of M dwarfs in the search for potentially habitable Earth-sized planets has grown significantly in the last years. Aims. In our on-going effort to comprehensively and accurately characterise confirmed and potential planet-hosting M dwarfs, in particular for the CARMENES survey, we have carried out a comprehensive multi-band photometric analysis involving spectral energy distributions, luminosities, absolute magnitudes, colours, and spectral types, from which we have derived basic astrophysical parameters. Methods. We have carefully compiled photometry in 20 passbands from the ultraviolet to the mid-infrared, and combined it with the latest parallactic distances and close-multiplicity information, mostly from Gaia DR2, of a sample of 2479 K5 V to L8 stars and ultracool dwarfs, including 2210 nearby, bright M dwarfs. For this, we made extensive use of Virtual Observatory tools. Results. We have homogeneously computed accurate bolometric luminosities and effective temperatures of 1843 single stars, derived their radii and masses, studied the impact of metallicity, and compared our results with the literature. The over 40 000 individually inspected magnitudes, together with the basic data and derived parameters of the stars, individual and averaged by spectral type, have been made public to the astronomical community. In addition, we have reported 40 new close multiple systems and candidates (ρ <  3.3 arcsec) and 36 overluminous stars that are assigned to young Galactic populations. Conclusions. In the new era of exoplanet searches around M dwarfs via transit (e.g. TESS, PLATO) and radial velocity (e.g. CARMENES, NIRPS+HARPS), this work is of fundamental importance for stellar and therefore planetary parameter determination.

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.

Sign in / Sign up

Export Citation Format

Share Document