The population of M dwarfs observed at low radio frequencies

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.

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A circular polarization survey for radio stars with the Australian SKA Pathfinder

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stab299 ◽

2021 ◽

Vol 502 (4) ◽

pp. 5438-5454

Author(s):

Joshua Pritchard ◽

Tara Murphy ◽

Andrew Zic ◽

Christene Lynch ◽

George Heald ◽

...

Keyword(s):

Radio Emission ◽

Brightness Temperature ◽

Circular Polarization ◽

Flux Density ◽

Wide Band ◽

M Dwarfs ◽

Square Kilometre Array ◽

Population Statistics ◽

Chemically Peculiar ◽

Radio Stars

ABSTRACT We present results from a circular polarization survey for radio stars in the Rapid ASKAP Continuum Survey (RACS). RACS is a survey of the entire sky south of δ = +41○ being conducted with the Australian Square Kilometre Array Pathfinder telescope (ASKAP) over a 288 MHz wide band centred on 887.5 MHz. The data we analyse include Stokes I and V polarization products to an RMS sensitivity of 250 μJy PSF−1. We searched RACS for sources with fractional circular polarization above 6 per cent, and after excluding imaging artefacts, polarization leakage, and known pulsars we identified radio emission coincident with 33 known stars. These range from M-dwarfs through to magnetic, chemically peculiar A- and B-type stars. Some of these are well-known radio stars such as YZ CMi and CU Vir, but 23 have no previous radio detections. We report the flux density and derived brightness temperature of these detections and discuss the nature of the radio emission. We also discuss the implications of our results for the population statistics of radio stars in the context of future ASKAP and Square Kilometre Array surveys.

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The Solar Neighborhood. XLV. The Stellar Multiplicity Rate of M Dwarfs Within 25 pc

The Astronomical Journal ◽

10.3847/1538-3881/ab05dc ◽

2019 ◽

Vol 157 (6) ◽

pp. 216 ◽

Cited By ~ 35

Author(s):

Jennifer G. Winters ◽

Todd J. Henry ◽

Wei-Chun Jao ◽

John P. Subasavage ◽

Joseph P. Chatelain ◽

...

Keyword(s):

Solar Neighborhood ◽

M Dwarfs

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A Deep Large area Search for Low Luminosity Stars

Highlights of Astronomy ◽

10.1017/s1539299600021675 ◽

1998 ◽

Vol 11 (1) ◽

pp. 435-435

Author(s):

Hugh R.A. Jones ◽

Mike R.S. Hawkins

Keyword(s):

Spectral Type ◽

Low Temperatures ◽

Current Model ◽

Brown Dwarfs ◽

Evolutionary Models ◽

Spectral Indices ◽

Late Type ◽

Brown Dwarf ◽

Large Area ◽

M Dwarfs

In a recent survey for faint red stars from a digital stack of Schmidt plates a number of candidate objects were identified. Parallax’s for three of these objects have been reported showing them to have luminosities which interpreted within the available evolutionary models indicate them to be good brown dwarf candidates. Here we examine spectra of these objects and others from the plate stack. Using standard spectral indices we find that for a given spectral type their spectra are more consistent with the Pleiades brown dwarfs (PPL 15, Teide 1 and Calar 3) than with standard late-type M dwarfs. Our interpretation is that this is due to their selection by RF IN colours which at values > 3 preferentially selects objects with relatively low gravities. For late-type M dwarfs and brown dwarfs low gravities are expected to be a reliable indication of youth. We also notice that the stack objects generally have strong FeH absorption for their spectral type. Current model atmospheres suggest that FeH strongly increases in strength toward lower metallicities and lower temperatures. We believe that this is not consistent with the available observational evidence from late-type M dwarfs. It is possible that solid Fe is forming inthe low temperature atmospheres relatively depleting FeH strengths toward lower temperatures. We find some evidence that for dwarfs at low temperatures dust formation is less prevalent in lower gravity objects suggesting that dwarfs at low temperatures stronger FeH may be an indication of youth. In addition to the spectral evidence the three stack objects whose parallax’s have been measured show small tangential velocities which is a further indication of youth.

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Effects of various radio frequencies on combined drying and disinfestation treatments for in-shell walnuts

LWT ◽

10.1016/j.lwt.2021.111246 ◽

2021 ◽

pp. 111246

Author(s):

Yuxiao Mao ◽

Penghao Wang ◽

Yi Wu ◽

Lixia Hou ◽

Shaojin Wang

Keyword(s):

Radio Frequencies

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Spectra of M Dwarfs - Dimmed by Dust

Highlights of Astronomy ◽

10.1017/s1539299600021717 ◽

1998 ◽

Vol 11 (1) ◽

pp. 439-440

Author(s):

T. Tsuji ◽

K. Ohnaka ◽

W. Aoki ◽

H.R.A. Jones

Keyword(s):

Chemical Composition ◽

Brown Dwarfs ◽

Surface Chemical ◽

Basic Information ◽

M Dwarfs ◽

Surface Chemical Composition ◽

Molecular Lines ◽

Low Mass

Spectra of M dwarfs are rich in atomic and molecular lines. These spectra provide such basic information as Teff (or radius), log g (or mass), surface chemical composition, and something more (e.g. activity) if properly interpreted. It is recognized, however, that spectra of M dwarfs are already dimmed by the dust formed in their photospheres (Tsuji et al. 1996a) and this effect, which has been overlooked until recently, should be taken into account in any interpretation and analysis of the spectra of very low mass objects (VLMOs) including late M dwarfs and brown dwarfs.

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