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 Scans and Narrow-Band Photometry of Late-Type Stars in the One-Micron Region

1974 ◽  
Vol 3 ◽  
pp. 285-306 ◽  
Author(s):  
R. F. Wing
Keyword(s):  
Near Infrared ◽  
Narrow Band ◽  
M Dwarfs ◽  
Mira Variables ◽  
Near Infrared Spectra ◽  
First Results ◽  
System 2 ◽  
M Stars ◽  
Band Sequence ◽  
The One

AbstractA summary is given of the molecular bands occurring in the near-infrared spectra of cool stars, especially those having sufficient strength and freedom from contamination to be measurable by narrow-band photometry. In some cases useful indices of both temperature and luminosity can be obtained from such measurements. Several bands remain unidentified, including the 9910 Å band in late M dwarfs and at least nine bands in cool S stars.Three topics of a spectroscopic nature are discussed. (1) In Mira variables, grossly different spectral types are sometimes obtained from zero-volt and excited TiO bands of the same band system. (2) A few M stars have been found to show bands of’ both VO and CN at the same time. They may be the coolest known supergiants, although there remains some doubt as to their luminosities. (3) The first results are given from a program of measuring crude C12/C13 ratios from narrow-band photometry of sensitive points on the profile of the ∆υ = + 2 band sequence of CN. The observations require only a few minutes per star, and the method can be applied to G and K giants and supergiants as well as to carbon stars.

scholarly journals Diving Beneath the Sea of Stellar Activity: Chromatic Radial Velocities of the Young AU Mic Planetary System

2021 ◽  
Vol 162 (6) ◽  
pp. 295
Author(s):  
Bryson L. Cale ◽  
Michael Reefe ◽  
Peter Plavchan ◽  
Angelle Tanner ◽  
Eric Gaidos ◽  
...  
Keyword(s):  
Process Model ◽  
Near Infrared ◽  
Wavelength Dependence ◽  
M Dwarfs ◽  
Echelle Spectrograph ◽  
Stellar Activity ◽  
Transiting Planets ◽  
Order Of Magnitude ◽  
Modeling Toolkit ◽  
M Dwarf

Abstract We present updated radial-velocity (RV) analyses of the AU Mic system. AU Mic is a young (22 Myr) early-M dwarf known to host two transiting planets—P b ∼ 8.46 days, R b = 4.38 − 0.18 + 0.18 R ⊕ , P c ∼ 18.86 days, R c = 3.51 − 0.16 + 0.16 R ⊕ . With visible RVs from Calar Alto high-Resolution search for M dwarfs with Exo-earths with Near-infrared and optical echelle Spectrographs (CARMENES)-VIS, CHIRON, HARPS, HIRES, Minerva-Australis, and Tillinghast Reflector Echelle Spectrograph, as well as near-infrared (NIR) RVs from CARMENES-NIR, CSHELL, IRD, iSHELL, NIRSPEC, and SPIRou, we provide a 5σ upper limit to the mass of AU Mic c of M c ≤ 20.13 M ⊕ and present a refined mass of AU Mic b of M b = 20.12 − 1.57 + 1.72 M ⊕ . Used in our analyses is a new RV modeling toolkit to exploit the wavelength dependence of stellar activity present in our RVs via wavelength-dependent Gaussian processes. By obtaining near-simultaneous visible and near-infrared RVs, we also compute the temporal evolution of RV “color” and introduce a regressional method to aid in isolating Keplerian from stellar activity signals when modeling RVs in future works. Using a multiwavelength Gaussian process model, we demonstrate the ability to recover injected planets at 5σ significance with semi-amplitudes down to ≈10 m s−1 with a known ephemeris, more than an order of magnitude below the stellar activity amplitude. However, we find that the accuracy of the recovered semi-amplitudes is ∼50% for such signals with our model.

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 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 The Gaia Ultra-Cool Dwarf Sample – III: seven new multiple systems containing at least one Gaia DR2 ultracool dwarf.

2020 ◽  
Vol 494 (4) ◽  
pp. 4891-4906
Author(s):  
F Marocco ◽  
R L Smart ◽  
E E Mamajek ◽  
L M Sarro ◽  
A J Burgasser ◽  
...  
Keyword(s):  
Binary Systems ◽  
Near Infrared ◽  
Atmospheric Parameters ◽  
M Dwarfs ◽  
Wide Binary ◽  
Physical Separation ◽  
Multiple Systems ◽  
Low Mass ◽  
Release Data ◽  
Gaia Dr2

ABSTRACT We present 10 new ultracool dwarfs in seven wide binary systems discovered using Gaia second data release data, identified as part of our Gaia Ultra-Cool Dwarf Sample project. The seven systems presented here include an L1 companion to the G5 IV star HD 164507, an L1: companion to the V478 Lyr AB system, an L2 companion to the metal-poor K5 V star CD-28 8692, an M9 V companion to the young variable K0 V star LT UMa, and three low-mass binaries consisting of late Ms and early Ls. The HD 164507, CD-28 8692, V478 Lyr, and LT UMa systems are particularly important benchmarks, because the primaries are well characterized and offer excellent constraints on the atmospheric parameters and ages of the companions. We find that the M8 V star 2MASS J23253550+4608163 is ∼2.5 mag overluminous compared to M dwarfs of similar spectral type, but at the same time it does not exhibit obvious peculiarities in its near-infrared spectrum. Its overluminosity cannot be explained by unresolved binarity alone. Finally, we present an L1+L2 system with a projected physical separation of 959 au, making this the widest L + L binary currently known.

scholarly journals The CARMENES search for exoplanets around M dwarfs

2018 ◽  
Vol 615 ◽  
pp. A6 ◽  
Author(s):  
V. M. Passegger ◽  
A. Reiners ◽  
S. V. Jeffers ◽  
S. Wende-von Berg ◽  
P. Schöfer ◽  
...  
Keyword(s):  
High Resolution ◽  
Near Infrared ◽  
Stellar Atmosphere ◽  
Stellar Atmospheres ◽  
Surface Gravity ◽  
M Dwarfs ◽  
Low Mass Stars ◽  
Target Sample ◽  
M Dwarf ◽  
The Phoenix

Context. The new CARMENES instrument comprises two high-resolution and high-stability spectrographs that are used to search for habitable planets around M dwarfs in the visible and near-infrared regime via the Doppler technique. Aims. Characterising our target sample is important for constraining the physical properties of any planetary systems that are detected. The aim of this paper is to determine the fundamental stellar parameters of the CARMENES M-dwarf target sample from high-resolution spectra observed with CARMENES. We also include several M-dwarf spectra observed with other high-resolution spectrographs, that is CAFE, FEROS, and HRS, for completeness. Methods. We used a χ2 method to derive the stellar parameters effective temperature Teff, surface gravity logg, and metallicity [Fe/H] of the target stars by fitting the most recent version of the PHOENIX-ACES models to high-resolution spectroscopic data. These stellar atmosphere models incorporate a new equation of state to describe spectral features of low-temperature stellar atmospheres. Since Teff, logg, and [Fe/H] show degeneracies, the surface gravity is determined independently using stellar evolutionary models. Results. We derive the stellar parameters for a total of 300 stars. The fits achieve very good agreement between the PHOENIX models and observed spectra. We estimate that our method provides parameters with uncertainties of σTeff = 51 K, σlog g = 0.07, and σ[Fe/H] = 0.16, and show that atmosphere models for low-mass stars have significantly improved in the last years. Our work also provides an independent test of the new PHOENIX-ACES models, and a comparison for other methods using low-resolution spectra. In particular, our effective temperatures agree well with literature values, while metallicities determined with our method exhibit a larger spread when compared to literature results.

scholarly journals The CARMENES search for exoplanets around M dwarfs

2019 ◽  
Vol 632 ◽  
pp. A24
Author(s):  
B. Fuhrmeister ◽  
S. Czesla ◽  
L. Hildebrandt ◽  
E. Nagel ◽  
J. H. M. M. Schmitt ◽  
...  
Keyword(s):  
Near Infrared ◽  
Activity Levels ◽  
Line Formation ◽  
M Dwarfs ◽  
Complex Behaviour ◽  
X Ray ◽  
Solar Type ◽  
M Dwarf ◽  
Calar Alto ◽  
Important Activity

The He I infrared (IR) triplet at 10 830 Å is an important activity indicator for the Sun and in solar-type stars, however, it has rarely been studied in relation to M dwarfs to date. In this study, we use the time-averaged spectra of 319 single stars with spectral types ranging from M0.0 V to M9.0 V obtained with the CARMENES high resolution optical and near-infrared spectrograph at Calar Alto to study the properties of the He I IR triplet lines. In quiescence, we find the triplet in absorption with a decrease of the measured pseudo equivalent width (pEW) towards later sub-types. For stars later than M5.0 V, the He I triplet becomes undetectable in our study. This dependence on effective temperature may be related to a change in chromospheric conditions along the M dwarf sequence. When an emission in the triplet is observed, we attribute it to flaring. The absence of emission during quiescence is consistent with line formation by photo-ionisation and recombination, while flare emission may be caused by collisions within dense material. The He I triplet tends to increase in depth according to increasing activity levels, ultimately becoming filled in; however, we do not find a correlation between the pEW(He IR) and X-ray properties. This behaviour may be attributed to the absence of very inactive stars (LX∕Lbol < −5.5) in our sample or to the complex behaviour with regard to increasing depth and filling in.

scholarly journals The CARMENES search for exoplanets around M dwarfs

2018 ◽  
Vol 612 ◽  
pp. A49 ◽  
Author(s):  
A. Reiners ◽  
M. Zechmeister ◽  
J. A. Caballero ◽  
I. Ribas ◽  
J. C. Morales ◽  
...  
Keyword(s):  
High Resolution ◽  
Wavelength Range ◽  
Near Infrared ◽  
Signal To Noise Ratio ◽  
Rotation Velocity ◽  
Atmospheric Models ◽  
M Dwarfs ◽  
Low Mass Stars ◽  
Low Mass ◽  
M Dwarf

The CARMENES radial velocity (RV) survey is observing 324 M dwarfs to search for any orbiting planets. In this paper, we present the survey sample by publishing one CARMENES spectrum for each M dwarf. These spectra cover the wavelength range 520–1710 nm at a resolution of at least R >80 000, and we measure its RV, Hα emission, and projected rotation velocity. We present an atlas of high-resolution M-dwarf spectra and compare the spectra to atmospheric models. To quantify the RV precision that can be achieved in low-mass stars over the CARMENES wavelength range, we analyze our empirical information on the RV precision from more than 6500 observations. We compare our high-resolution M-dwarf spectra to atmospheric models where we determine the spectroscopic RV information content, Q, and signal-to-noise ratio. We find that for all M-type dwarfs, the highest RV precision can be reached in the wavelength range 700–900 nm. Observations at longer wavelengths are equally precise only at the very latest spectral types (M8 and M9). We demonstrate that in this spectroscopic range, the large amount of absorption features compensates for the intrinsic faintness of an M7 star. To reach an RV precision of 1 m s−1 in very low mass M dwarfs at longer wavelengths likely requires the use of a 10 m class telescope. For spectral types M6 and earlier, the combination of a red visual and a near-infrared spectrograph is ideal to search for low-mass planets and to distinguish between planets and stellar variability. At a 4 m class telescope, an instrument like CARMENES has the potential to push the RV precision well below the typical jitter level of 3–4 m s−1.

scholarly journals CARMENES: Calar Alto high-Resolution search for M dwarfs with Exo-earths with Near-infrared and optical Echelle Spectrographs

2010 ◽  
Vol 6 (S276) ◽  
pp. 545-546 ◽  
Author(s):  
Andreas Quirrenbach ◽  
Pedro J. Amado ◽  
José A. Caballero ◽  
Holger Mandel ◽  
Reinhard Mundt ◽  
...  
Keyword(s):  
High Resolution ◽  
Radial Velocity ◽  
Emission Line ◽  
Wavelength Range ◽  
Spectral Resolution ◽  
Near Infrared ◽  
M Dwarfs ◽  
Simultaneous Emission ◽  
M Stars ◽  
Calar Alto

AbstractCARMENES (Calar Alto high-Resolution search for M dwarfs with Exo-earths with Near-infrared and optical Echelle Spectrographs) is a next-generation instrument for the 3.5 m telescope at the Calar Alto Observatory. CARMENES will conduct a five-year exoplanet survey targeting ~300 M stars. The CARMENES instrument consists of two separate fiber-fed spectrographs covering the wavelength range from 0.52 to 1.7 μm at a spectral resolution of R = 85,000. The spectrographs are housed in a temperature-stabilized environment in vacuum tanks, to enable a 1 m/s radial velocity precision employing a simultaneous emission-line calibration.

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.

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