scholarly journals Analysis of the TiO isotopologues in stellar optical spectra

2020 ◽  
Vol 642 ◽  
pp. A77 ◽  
Author(s):  
Ya. V. Pavlenko ◽  
Sergei N. Yurchenko ◽  
Laura K. McKemmish ◽  
Jonathan Tennyson
Keyword(s):  
Optical Spectra ◽  
Isotopic Ratios ◽  
M Dwarfs ◽  
Line List ◽  
Isotopic Abundances ◽  
Atomic Lines ◽  
M Stars ◽  
Spectral Ranges ◽  
M Dwarf ◽  
Better Than

Context. We used the new ExoMol TiO rovibronic line lists to identify and model TiO isotopologue features in spectra of M dwarfs. Aims. We investigate problems involving the computation of electronic bands for different isotopologues of TiO by modelling optical spectra of late-type stars. Based on this, we determine their Ti isotopic abundances and compare the TiO isotopologue spectra computed using line lists by different authors. Methods. We fitted theoretical synthetic spectra to the observed stellar molecular bands of TiO. We modelled spectra of two M dwarfs, GJ 15A (M1V) and GJ 15B (M3 V), to determine Ti isotopic ratios in their atmospheres. Results. We demonstrate the accuracy of the ExoMol TOTO line list for different isotopologues of TiO and the possibility of determining accurate Ti isotope abundances in a number of spectral ranges. The 7580–7594 Å spectral range seems particularly useful, with two atomic lines of Fe I and molecular band heads of 50Ti O, 49Ti O, 48Ti O, and 47Ti O clearly observable in our two M-dwarf spectra. We determine non-solar Ti isotopic ratios of 46Ti, 47Ti, 48Ti, 49Ti, and 50Ti of 7.9, 5.2, 72.8, 7.9, and 6.2 for GJ 15A and 7.4, 4.2, 76.6, 5.8, and 6.0 for GJ 15B with an accuracy of ±0.2. [Ti] = 0.040 and 0.199 and within an accuracy of ±0.10 were also determined for GJ 15A and GJ 15B, respectively. Conclusions. We find that the ExoMol TOTO TiO line list (a) describes the fine details in line position and intensity of the M-dwarf spectra better than other available TiO line lists, (b) correctly reproduces the positions and intensities of the TiO isotopologue band heads observed in M-dwarf spectra, and (c) can be used to determine Ti isotope abundances in atmospheres of M stars.

scholarly journals The Mass-Luminosity Relation From Binaries

1998 ◽  
Vol 11 (1) ◽  
pp. 419-420
Author(s):  
David W. Latham
Keyword(s):  
Eclipsing Binaries ◽  
M Dwarfs ◽  
Direct Measurements ◽  
Nearby Stars ◽  
The Masses ◽  
Stellar Masses ◽  
M Dwarf ◽  
Magnitude Difference ◽  
Astrometric Binaries ◽  
Better Than

What is known about the masses of main-sequence stars from the analysis of binary orbits? Double-lined eclipsing binaries are the main source of very precise stellar masses and radii (e.g. Andersen 1997), contributing more than 100 determinations with better than 2% precision over the range 0.6 to 20 Mʘ. For lower-mass stars we are forced to turn to nearby systems with astrometric orbits (e.g. Henry et al. 1993). Not only is the number of good mass determinations from such systems smaller, but also the precision is generally poorer. We are approaching an era when interferometers should have a major impact by supplying good astrometric orbits for dozens of double-lined systems. Already we are beginning to see the sorts of results to expect from this (e.g. Torres et al. 1997). Figure 1. Mass vs. absolute V magnitude for eclipsing binaries (circles) and nearby astrometric binaries (squares) Figure 1 is an updated version of a diagram presented by Henry et al. (1993, their Figure 2). It shows the general run of mass determinations from about 10 Mʘ down to the substellar limit near 0.075 Mʘ. Ninety of the points in Figure 1 are for eclipsing binary masses from Andersen’s review (1991) and are plotted as open circles. The results for eclipsing binaries published since 1991 are plotted as 30 filled circles, adopting the same limit of 2% for the mass precision. In most cases the uncertainties are similar to the size of the symbols. Especially noteworthy is the pair of new points for CM Draconis (Metcalfe et al. 1996) with masses near 0.25 Mʘ. Together with the points for YY Geminorum near 0.6 Mʘ, these are the only M dwarfs that have precise mass determinations. For the most part we are forced to rely on nearby stars with astrometric orbits, to fill in the M dwarf region of the diagram. We have used filled squares in Figure 1 for 29 such systems from Henry et al. (1993), updated using 14 new parallaxes from Hipparcos and 4 from the new Yale Parallax Catalog (1995). Gliese 508 is not included, because it is now known to be a triple, while Gliese 67AB, 570BC, and 623AB are not included because there are not yet any direct measurements of the V magnitude difference for these systems.

scholarly journals The Near Infrared FeH Lines as Indicators of Surface Gravity of M stars

1996 ◽  
Vol 171 ◽  
pp. 441-441
Author(s):  
Ricardo Piorno Schiavon ◽  
Beatriz Barbuy
Keyword(s):  
Near Infrared ◽  
Synthesis Method ◽  
Population Synthesis ◽  
Atmospheric Parameters ◽  
M Dwarfs ◽  
Synthetic Spectra ◽  
Iron Hydride ◽  
M Stars ◽  
M Dwarf ◽  
Ongoing Project

We compute synthetic spectra in the region around 1 μm, including the Wing-Ford band (WFB) of Iron Hydride (FeH) in the calculations. This band is known to be a good indicator of surface gravities of M stars. Employing Kurucz model atmospheres, we study the response of the intensity of the WFB to atmospheric parameters and check our results against observations of M dwarfs. This study is part of an ongoing project which aims to investigate the M dwarf-to-giant ratio in galaxies, through a population synthesis method, exploring a number of spectral indicators in the near infrared, such as the WFB, the NaI, CaII and CO near infrared features.

scholarly journals Occurrence rates of planets orbiting M Stars: applying ABC to Kepler DR25, Gaia DR2, and 2MASS data

2020 ◽  
Vol 498 (2) ◽  
pp. 2249-2262 ◽  
Author(s):  
Danley C Hsu ◽  
Eric B Ford ◽  
Ryan Terrien
Keyword(s):  
Small Sample ◽  
Occurrence Rate ◽  
Early Type ◽  
M Dwarfs ◽  
Orbital Periods ◽  
M Stars ◽  
Stellar Properties ◽  
Approximate Bayesian ◽  
M Dwarf ◽  
Gaia Dr2

ABSTRACT We present robust planet occurrence rates for Kepler planet candidates around M stars for planet radii Rp = 0.5–4 R⊕ and orbital periods P = 0.5–256 d using the approximate Bayesian computation technique. This work incorporates the final Kepler DR25 planet candidate catalogue and data products and augments them with updated stellar properties using Gaia DR2 and 2MASS point source catalogue. We apply a set of selection criteria to select a sample of 1746 Kepler M dwarf targets that host 89 associated planet candidates. These early-type M dwarfs and late K dwarfs were selected from cross-referenced targets using several photometric quality flags from Gaia DR2 and colour–magnitude cuts using 2MASS magnitudes. We estimate a habitable zone occurrence rate of $f_{\textrm {M,HZ}} = 0.33^{+0.10}_{-0.12}$ for planets with 0.75–1.5 R⊕ size. We caution that occurrence rate estimates for Kepler M stars are sensitive to the choice of prior due to the small sample of target stars and planet candidates. For example, we find an occurrence rate of $4.2^{+0.6}_{-0.6}$ or $8.4^{+1.2}_{-1.1}$ planets per M dwarf (integrating over Rp = 0.5–4 R⊕ and P = 0.5–256 d) for our two choices of prior. These occurrence rates are greater than those for FGK dwarf target when compared at the same range of orbital periods, but similar to occurrence rates when computed as a function of equivalent stellar insolation. Combining our result with recent studies of exoplanet architectures indicates that most, and potentially all, early-type M dwarfs harbour planetary systems.

scholarly journals High-resolution spectroscopy of flares and CMEs on AD Leonis

2020 ◽  
Vol 637 ◽  
pp. A13 ◽  
Author(s):  
P. Muheki ◽  
E. W. Guenther ◽  
T. Mutabazi ◽  
E. Jurua
Keyword(s):  
High Resolution ◽  
Spectral Lines ◽  
High Resolution Spectroscopy ◽  
Flare Activity ◽  
The Sun ◽  
M Dwarfs ◽  
Highly Active ◽  
M Stars ◽  
High Level ◽  
M Dwarf

Context. Flares and coronal mass ejections (CMEs) are important for the evolution of the atmospheres of planets and their potential habitability, particularly for planets orbiting M stars at a distance <0.4 AU. Detections of CMEs on these stars have been sparse, and previous studies have therefore modelled their occurrence frequency by scaling up solar relations. However, because the topology and strength of the magnetic fields on M stars is different from that of the Sun, it is not obvious that this approach works well. Aims. We used a large number of high-resolution spectra to study flares, CMEs, and their dynamics of the active M dwarf star AD Leo. The results can then be used as reference for other M dwarfs. Methods. We obtained more than 2000 high-resolution spectra (R ~ 35 000) of the highly active M dwarf AD Leo, which is viewed nearly pole on. Using these data, we studied the behaviour of the spectral lines Hα, Hβ, and He I 5876 in detail and investigated asymmetric features that might be Doppler signatures of CMEs. Results. We detected numerous flares. The largest flare emitted 8.32 × 1031 erg in Hβ and 2.12 × 1032 erg in Hα. Although the spectral lines in this and other events showed a significant blue asymmetry, the velocities associated with it are far below the escape velocity. Conclusions. Although AD Leo shows a high level of flare activity, the number of CMEs is relatively low. It is thus not appropriate to use the same flare-to-CME relation for M dwarfs as for the Sun.

M stars in the region of the Pleiades

1966 ◽  
Vol 24 ◽  
pp. 367
Author(s):  
M. F. McCarthy ◽  
P. J. Treanor
Keyword(s):  
Main Sequence ◽  
Individual Identification ◽  
Evolutionary Status ◽  
Proper Motions ◽  
Surface Distribution ◽  
Objective Prism ◽  
M Stars ◽  
Spectral Ranges ◽  
M Dwarf ◽  
Natural Groups

An objective-prism survey in the infrared of a region 4°6, square centred on the Pleiades has been made with the Vatican Schmidt and its 2°5 prism in a search for M dwarf members of this cluster. One hundred and twenty-five stars have been classified into four natural groups which correspond to possible dwarfs in the spectral ranges M2-M3, M0-M1, K7-K9 and to non-member field giants of types M0-M4. Provisional blue magnitudes have been obtained by photographic interpolation from photo-electricBmagnitudes of Johnson and Mitchell using an electronic reduction programme by Bertiau which incorporates a sky background correction. Positional, photometric, proper motion and spectral data are provided in a catalogue which is supplemented by individual identification charts. An analysis of the surface distribution, magnitudes and proper motions of the stars indicates that the first three groups contain many cluster members. A select list contains 27 stars mostly fainter thanB= 16 which are considered probable cluster members. The material is discussed in relation to the evolutionary status of the cluster. Our results show that a well-populated main sequence of early M stars is present down toB= 17.

scholarly journals NLTE model atmospheres for M dwarfs and giants

1996 ◽  
Vol 176 ◽  
pp. 539-546 ◽  
Author(s):  
Peter H. Hauschildt ◽  
France Allard ◽  
David R. Alexander ◽  
Andreas Schweitzer ◽  
E. Baron
Keyword(s):  
Flux Distribution ◽  
M Dwarfs ◽  
Atmospheric Structure ◽  
Optical Continuum ◽  
Vibrational Bands ◽  
Atomic Lines ◽  
M Stars ◽  
Molecular Compounds ◽  
Flux Redistribution

The atmospheres of M stars are dominated by a small number of very strong molecular compounds (H2O, TiO, H2, CO, VO). Most of the hydrogen is locked in molecular H2, most of the carbon in CO; and H2O, TiO and VO opacities define a pseudo-continuum covering the entire flux distribution of these stars. The optical “continuum” is due to TiO vibrational bands which are often used as temperature indicators for these stars. These may be the depth of the bands relative to the troughs in between them; or the depth of the VO bands; or of the atomic lines relative to the local “continuum”; or even the strength of the infrared water bands; all of these depend on the strength of the TiO bands and the amount of flux-redistribution to longer wavelengths exerted by them. Departures from LTE of the Ti I atom, and thus the concentration of the important TiO molecule, could, therefore, have severe and measurable consequences on the atmospheric structure and spectra of these stars.

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 &lt;0.6 R⊙, with the average error being 3%. Our catalog enables efficient sample selection for exoplanet surveys around nearby M-type dwarfs.

Selection of M-dwarfs using Gaia, WISE, and 2MASS

2019 ◽  
Vol 490 (3) ◽  
pp. 4107-4120
Author(s):  
J Bentley ◽  
C G Tinney ◽  
S Sharma ◽  
D Wright
Keyword(s):  
Absolute Magnitude ◽  
Contamination Rate ◽  
M Dwarfs ◽  
Sky Survey ◽  
Model Predictions ◽  
Galaxy Model ◽  
M Dwarf ◽  
Different Sources ◽  
Sources Of Contamination ◽  
Selection Of

ABSTRACT We present criteria for the selection of M-dwarfs down to G < 14.5 using all-sky survey data, with a view to identifying potential M-dwarfs, to be confirmed spectroscopically by the FunnelWeb survey. Two sets of criteria were developed. The first, based on absolute magnitude in the Gaia G passband, with MG > 7.7, selects 76,392 stars, with 81.0 per cent expected to be M-dwarfs at a completeness of >97 per cent. The second is based on colour and uses Gaia, WISE, and 2MASS all-sky photometry. This criteria identifies 94,479 candidate M-dwarfs, of which between 29.4 per cent and 47.3 per cent are expected to be true M-dwarfs, and which contains 99.6 per cent of expected M-dwarfs. Both criteria were developed using synthetic galaxy model predictions, and a previously spectroscopically classified set of M- and K-dwarfs, to evaluate both M-dwarf completeness and false-positive detections (i.e. the non-M-dwarf contamination rate). Both criteria used in combination demonstrate how each excludes different sources of contamination. We therefore developed a final set of criteria that combines absolute magnitude and colour selection to identify 74,091 stars. All these sets of criteria select numbers of objects feasible for confirmation via massively multiplexed spectroscopic surveys like FunnelWeb.

scholarly journals Giant planets around AF and M stars

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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