A FIRST LOOK AT ROTATION IN INACTIVE LATE-TYPE 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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Giant planets around AF and M stars

Proceedings of the International Astronomical Union ◽

10.1017/s1743921313007898 ◽

2013 ◽

Vol 8 (S299) ◽

pp. 64-65

Author(s):

Julien Rameau ◽

Gaël Chauvin ◽

Anne-Marie Lagrange ◽

Philippe Delorme ◽

Justine Lannier

Keyword(s):

Giant Planets ◽

Early Type ◽

Late Type ◽

M Dwarfs ◽

Low Mass Stars ◽

Planetary Mass ◽

Nearby Stars ◽

Low Mass ◽

M Stars ◽

The One

AbstractWe present the results of two three-year surveys of young and nearby stars to search for wide orbit giant planets. On the one hand, we focus on early-type and massive, namely β Pictoris analogs. On the other hand, we observe late type and very low mass stars, i.e., M dwarfs. We report individual detections of new planetary mass objects. According to our deep detection performances, we derive the observed frequency of giant planets between these two classes of parent stars. We find frequency between 6 to 12% but we are not able to assess a/no correlation with the host-mass.

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AN ACTIVITY–ROTATION RELATIONSHIP AND KINEMATIC ANALYSIS OF NEARBY MID-TO-LATE-TYPE M DWARFS

The Astrophysical Journal ◽

10.1088/0004-637x/812/1/3 ◽

2015 ◽

Vol 812 (1) ◽

pp. 3 ◽

Cited By ~ 80

Author(s):

Andrew A. West ◽

Kolby L. Weisenburger ◽

Jonathan Irwin ◽

Zachory K. Berta-Thompson ◽

David Charbonneau ◽

...

Keyword(s):

Kinematic Analysis ◽

Late Type ◽

M Dwarfs

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

Proceedings of the International Astronomical Union ◽

10.1017/s1743921314002014 ◽

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.

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PHOENIX model chromospheres of mid- to late-type M dwarfs

Astronomy and Astrophysics ◽

10.1051/0004-6361:20042338 ◽

2005 ◽

Vol 439 (3) ◽

pp. 1137-1148 ◽

Cited By ~ 31

Author(s):

B. Fuhrmeister ◽

J. H. M. M. Schmitt ◽

P. H. Hauschildt

Keyword(s):

Late Type ◽

M Dwarfs

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A Large, Deep Survey of the Taurus Dark Clouds

Symposium - International Astronomical Union ◽

10.1017/s0074180900210310 ◽

2003 ◽

Vol 211 ◽

pp. 79-80

Author(s):

S. L. Osborne ◽

R. F. Jameson ◽

P. D. Dobbie ◽

E. L. Martín

Keyword(s):

Spectroscopic Data ◽

Brown Dwarfs ◽

Theoretical Models ◽

Late Type ◽

M Dwarfs ◽

Dark Cloud ◽

Dark Clouds ◽

Deep Survey ◽

Hα Emission

Preliminary results from a deep R, I and Z band survey of ~ 6 square degrees of the Taurus Dark Cloud region are presented. 186 potential brown dwarfs have been unearthed, with seven having follow-up spectroscopic data. The spectra reveal three mid/late-type M dwarfs, of which two show weak Hα emission. If these objects are members of the TDC region, theoretical models suggest masses in the range 10 – 20 MJ.

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CCD Parallaxes for Southern Very Low Luminosity Stars

Symposium - International Astronomical Union ◽

10.1017/s0074180900172961 ◽

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.

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Model Atmospheres and the Teff Scale for M Dwarfs

Publications of the Astronomical Society of Australia ◽

10.1017/s1323358000025789 ◽

1993 ◽

Vol 10 (3) ◽

pp. 250-253 ◽

Cited By ~ 10

Author(s):

John M. Brett ◽

Bertrand Plez

Keyword(s):

Effective Temperature ◽

Preliminary Analysis ◽

Temperature Scale ◽

Sampling Technique ◽

Model Atmosphere ◽

Late Type ◽

M Dwarfs ◽

Good Test ◽

Laboratory Values ◽

Preliminary Model

AbstractThe Teff (effective temperature) scale for M dwarfs is very uncertain. One method which can be used to establish this scale is to compare observed spectra to synthetic ones derived from appropriate model atmospheres. With this method the adequacy of the model atmosphere is of great importance and simple models can give incorrect results. Alternatively if the Teff scale is known with some accuracy then this comparison is a good test of the adequacy of the models. We have computed some new and preliminary model atmospheres for late type dwarfs which accurately treat the line opacity with the opacity sampling technique and employ laboratory values for the transition strengths of molecular bands. With the above two considerations in mind we compare the fluxes of these models to observed fluxes of late K and early M dwarfs. This preliminary analysis indicates a discrepancy with the currently accepted Teff scale for early M dwarfs with the models suggesting values some 200 K hotter.

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