scholarly journals Photospheric properties and fundamental parameters of M dwarfs

2018 ◽  
Vol 610 ◽  
pp. A19 ◽  
Author(s):  
A.S. Rajpurohit ◽  
F. Allard ◽  
G. D. C. Teixeira ◽  
D. Homeier ◽  
S. Rajpurohit ◽  
...  
Keyword(s):  
High Resolution ◽  
Effective Temperature ◽  
Spectral Synthesis ◽  
High Spectral Resolution ◽  
M Dwarfs ◽  
Fundamental Parameters ◽  
Fundamental Information ◽  
The Galaxy ◽  
Fundamental Stellar Parameters ◽  
Band Spectra

Context. M dwarfs are an important source of information when studying and probing the lower end of the Hertzsprung-Russell (HR) diagram, down to the hydrogen-burning limit. Being the most numerous and oldest stars in the galaxy, they carry fundamental information on its chemical history. The presence of molecules in their atmospheres, along with various condensed species, complicates our understanding of their physical properties and thus makes the determination of their fundamental stellar parameters more challenging and difficult. Aim. The aim of this study is to perform a detailed spectroscopic analysis of the high-resolution H-band spectra of M dwarfs in order to determine their fundamental stellar parameters and to validate atmospheric models. The present study will also help us to understand various processes, including dust formation and depletion of metals onto dust grains in M dwarf atmospheres. The high spectral resolution also provides a unique opportunity to constrain other chemical and physical processes that occur in a cool atmosphere. Methods. The high-resolution APOGEE spectra of M dwarfs, covering the entire H-band, provide a unique opportunity to measure their fundamental parameters. We have performed a detailed spectral synthesis by comparing these high-resolution H-band spectra to that of the most recent BT-Settl model and have obtained fundamental parameters such as effective temperature, surface gravity, and metallicity (Teff, log g, and [Fe/H]), respectively. Results. We have determined Teff, log g, and [Fe/H] for 45 M dwarfs using high-resolution H-band spectra. The derived Teff for the sample ranges from 3100 to 3900 K, values of log g lie in the range 4.5 ≤ log g ≤ 5.5, and the resulting metallicities lie in the range −0.5 ≤ [Fe/H] ≤ +0.5. We have explored systematic differences between effective temperature and metallicity calibrations with other studies using the same sample of M dwarfs. We have also shown that the stellar parameters determined using the BT-Settl model are more accurate and reliable compared to other comparative studies using alternative models.

scholarly journals First results from MFOSC-P: low-resolution optical spectroscopy of a sample of M dwarfs within 100 parsecs

2020 ◽  
Vol 492 (4) ◽  
pp. 5844-5852 ◽  
Author(s):  
A S Rajpurohit ◽  
Vipin Kumar ◽  
Mudit K Srivastava ◽  
F Allard ◽  
D Homeier ◽  
...  
Keyword(s):  
Effective Temperature ◽  
Spectral Synthesis ◽  
Surface Gravity ◽  
Low Resolution ◽  
M Dwarfs ◽  
Physical Research Laboratory ◽  
Fundamental Parameters ◽  
Faint Object ◽  
First Results

ABSTRACT Mt Abu Faint Object Spectrograph and Camera (MFOSC-P) is an in-house-developed instrument for the Physical Research Laboratory (PRL) 1.2 m telescope at Mt Abu, India, commissioned in 2019 February. Here we present the first science results derived from the low-resolution spectroscopy programme of a sample of M dwarfs carried out during the commissioning run of MFOSC-P between 2019 February and June. M dwarfs carry great significance for exoplanet searches in the habitable zone and are among the promising candidates for the observatory’s several ongoing observational campaigns. Determination of their accurate atmospheric properties and fundamental parameters is essential to constrain both their atmospheric and evolutionary models. In this study, we provide a low-resolution (R ∼ 500) spectroscopic catalogue of 80 bright M dwarfs (J < 10) and classify them using their optical spectra. We have also performed spectral synthesis and χ2 minimization techniques to determine their fundamental parameters regarding effective temperature and surface gravity by comparing the observed spectra with the most recent BT-Settl synthetic spectra. The spectral type of M dwarfs in our sample ranges from M0 to M5. The derived effective temperature and surface gravity range from 4000–3000 K and 4.5–5.5 dex, respectively. In most of the cases, the derived spectral types are in good agreement with previously assigned photometric classifications.

scholarly journals Exploring the stellar properties of M dwarfs with high-resolution spectroscopy from the optical to the near-infrared

2018 ◽  
Vol 620 ◽  
pp. A180 ◽  
Author(s):  
A. S. Rajpurohit ◽  
F. Allard ◽  
S. Rajpurohit ◽  
R. Sharma ◽  
G. D. C. Teixeira ◽  
...  
Keyword(s):  
High Resolution ◽  
Near Infrared ◽  
Spectral Synthesis ◽  
Model Atmosphere ◽  
High Resolution Spectroscopy ◽  
Cloud Formation ◽  
M Dwarfs ◽  
Near Infrared Spectra ◽  
The Galaxy ◽  
Stellar Properties

Context. Being the most numerous and oldest stars in the galaxy, M dwarfs are objects of great interest for exoplanet searches. The presence of molecules in their atmosphere complicates our understanding of their atmospheric properties. But great advances have recently been made in the modeling of M dwarfs due to the revision of solar abundances. Aims. We aim to determine stellar parameters of M dwarfs using high resolution spectra (R ∼ 90 000) simultaneously in the visible and the near-infrared. The high resolution spectra and broad wavelength coverage provide an unique opportunity to understand the onset of dust and cloud formation at cool temperatures. Furthermore, this study will help in understanding the physical processes which occur in a cool atmospheres, particularly, the redistribution of energy from the optical to the near-infrared. Methods. The stellar parameters of M dwarfs in our sample have been determined by comparing the high resolution spectra both in the optical and in the near-infrared simultaneously observed by CARMENES with the synthetic spectra obtained from the BT-Settl model atmosphere. The detailed spectral synthesis of these observed spectra both in the optical and in the near-infrared helps to understand the missing continuum opacity. Results. For the first time, we derive fundamental stellar parameters of M dwarfs using the high resolution optical and near-infrared spectra simultaneously. We determine Teff, log g and [M/H] for 292 M dwarfs of spectral type M0 to M9, where the formation of dust and clouds are important. The derived Teff for the sample ranges from 2300 to 4000 K, values of log g ranges from 4.5 ≤ logg ≤ 5.5 and the resulting metallicity ranges from −0.5 ≤ [M/H] ≤ +0.5. We have also explored the possible differences in Teff, log g and [M/H] by comparing them with other studies of the same sample of M dwarfs.

scholarly journals Accurate Fundamental Stellar Parameters

2009 ◽  
Vol 5 (S265) ◽  
pp. 215-216
Author(s):  
Hans Bruntt
Keyword(s):  
Spectral Type ◽  
Effective Temperature ◽  
Direct Methods ◽  
Space Missions ◽  
Indirect Methods ◽  
Fundamental Parameters ◽  
Spectroscopic Analyses ◽  
Solar Type ◽  
Fundamental Stellar Parameters

AbstractWe combine results from interferometry, asteroseismology and spectroscopic analyses to determine accurate fundamental parameters (mass, radius and effective temperature) of 10 bright solar-type stars covering the H-R diagram from spectral type F5 to K1. Using “direct” techniques that are only weakly model-dependent we determine the mass, radius and effective temperature. We demonstrate that model-dependent or “indirect” methods can be reliably used even for relatively faint single stars for which direct methods are not applicable. This is important for the characterization of the targets of the CoRoT and Kepler space missions.

scholarly journals Magnetic fields in M-dwarfs from high-resolution infrared spectroscopy

2013 ◽  
Vol 9 (S302) ◽  
pp. 170-173
Author(s):  
D. Shulyak ◽  
A. Reiners ◽  
U. Seemann ◽  
O. Kochukhov ◽  
N. Piskunov
Keyword(s):  
High Resolution ◽  
Magnetic Fields ◽  
Spectral Synthesis ◽  
Strong Line ◽  
M Dwarfs ◽  
Low Mass Stars ◽  
Depth Analysis ◽  
Low Mass ◽  
Atomic Lines

AbstractAccurate spectroscopic measurements of magnetic fields in low mass stars remain challenging because of their cool temperatures, strong line blending, and often fast rotation. This is why previous estimates were based either on the analysis of only a few lines or made use of some indirect techniques. This frequently led to noticeable scatter in obtained results. In this talk I will present and discuss new results on the determination of the intensity and geometry of the magnetic fields in M-dwarfs using IR observations obtained with CRIRES@VLT. The instrument provides unprecedented data of high resolution (R = 100 000) which is crucial for resolving individual magnetically broadened molecular and atomic lines. Such an in-depth analysis based on direct magnetic spectral synthesis opens a possibility to deduce both field intensity and geometry avoiding most of the limitation and assumptions made in previous studies.

scholarly journals From solar to stellar brightness variations

2018 ◽  
Vol 619 ◽  
pp. A146 ◽  
Author(s):  
V. Witzke ◽  
A. I. Shapiro ◽  
S. K. Solanki ◽  
N. A. Krivova ◽  
W. Schmutz
Keyword(s):  
Effective Temperature ◽  
Magnetic Activity ◽  
The Sun ◽  
Physical Reason ◽  
Photometric Variability ◽  
Stellar Spectra ◽  
Fundamental Parameters ◽  
Brightness Change ◽  
Solar Metallicity ◽  
Fundamental Stellar Parameters

Context. Comparison studies of Sun-like stars with the Sun suggest an anomalously low photometric variability of the Sun compared to Sun-like stars with similar magnetic activity. Comprehensive understanding of stellar variability is needed to find a physical reason for this observation. Aims. We investigate the effect of metallicity and effective temperature on the photometric brightness change of Sun-like stars seen at different inclinations. The considered range of fundamental stellar parameters is sufficiently small so the stars investigated here still count as Sun-like or even as solar twins. Methods. To model the brightness change of stars with solar magnetic activity, we extended a well-established model of solar brightness variations based on solar spectra, Spectral And Total Irradiance REconstruction (SATIRE), to stars with different fundamental parameters. For this we calculated stellar spectra for different metallicities and effective temperature using the radiative transfer code ATLAS9. Results. We show that even a small change (e.g. within the observational error range) of metallicity or effective temperature significantly affects the photometric brightness change compared to the Sun. We find that for Sun-like stars, the amplitude of the brightness variations obtained for Strömgren (b + y)/2 reaches a local minimum for fundamental stellar parameters close to the solar metallicity and effective temperature. Moreover, our results show that the effect of inclination decreases for metallicity values greater than the solar metallicity. Overall, we find that an exact determination of fundamental stellar parameters is crucially important for understanding stellar brightness changes.

scholarly journals Multiple Supernova Explosions in a Forming Galaxy

2004 ◽  
Vol 21 (2) ◽  
pp. 232-236 ◽  
Author(s):  
Masao Mori ◽  
Masayuki Umemura ◽  
Andrea Ferrara
Keyword(s):  
High Resolution ◽  
Galaxy Formation ◽  
Spectral Synthesis ◽  
Formation Rate ◽  
Hydrodynamic Simulations ◽  
Lyman Break Galaxies ◽  
Large Spread ◽  
The Galaxy ◽  
Supernova Explosions ◽  
Grid Points

AbstractUltra-high resolution hydrodynamic simulations using 10243 grid points are performed of a very large supernova burst in a forming galaxy, with properties similar to those inferred for Lyman Break Galaxies (LBGs). Explosions produce kpc-sized expanding hot bubbles enclosed by cool, dense shells, and the engulfed gas is polluted with freshly-synthesised heavy elements. We show that the resultant inhomogeneous mixing produces a large spread ([Fe/H] ≈ –1 to –5) of metallicities, which affects the subsequent galactic chemical evolution and leaves its imprint on metal-poor stars. By combining a spectral synthesis model with the numerical results, we predict Lyα emission from such galaxy at z = 3. We find that the simulated galaxy, whose peak star formation rate is ≈200 M⊙ yr–1, produces a Lyα luminosity Lα = 9.7 × 1042 erg s–1. This value favorably matches the observed one, but some discrepancies are left for the Lyα line width, the metallicity, and X-ray properties. Since the results of the simulation is applicable only at the very early epoch of the galaxy formation, the metallicity is still lower than that of LBGs. However, the analysis presented here demonstrates a way to enable a systematic comparison with observational data.It is concluded that LBGs are optimal objects to scrutinise the early self-enrichment in forming galaxies. In the future, the predicted bubbly structure carved by SNe may be directly detected by high resolution observations with JWST.

scholarly journals Interstellar sodium and Galactic structure. A high-resolution survey

1985 ◽  
Vol 106 ◽  
pp. 325-328
Author(s):  
E. Maurice ◽  
A. Ardeberg ◽  
H. Lindgren
Keyword(s):  
High Resolution ◽  
Spectral Resolution ◽  
Absorption Lines ◽  
High Spectral Resolution ◽  
Line Of Sight ◽  
Substantial Part ◽  
Galactic Rotation ◽  
Interstellar Gas ◽  
Interstellar Clouds ◽  
The Galaxy

Observation of absorption lines produced by interstellar gas is a straight-forward way to determine column densities and velocities along the line of sight of interstellar clouds. In practice, peculiar motions often mask galactic rotation and/or cause line blending. We have made a study of absorption lines of interstellar sodium covering a substantial part of the Galaxy at extremely high spectral resolution.

scholarly journals Metallicity of M dwarfs: The link to exoplanets

2010 ◽  
Vol 6 (S276) ◽  
pp. 443-444
Author(s):  
V. Neves ◽  
X. Bonfils ◽  
N. C. Santos
Keyword(s):  
M Dwarfs ◽  
Fundamental Parameters ◽  
V Band ◽  
The Galaxy ◽  
M Stars ◽  
Baryonic Mass

AbstractThe determination of the stellar parameters of M dwarfs is of prime importance in the fields of galactic, stellar and planetary astronomy. M stars are the least studied galactic component regarding their fundamental parameters. Yet, they are the most numerous stars in the galaxy and contribute to most of its total (baryonic) mass. In particular, we are interested in their metallicity in order to study the star-planet connection and to refine the planetary parameters. As a preliminary result we present a test of the metallicity calibrations of Bonfils et al. (2005), Johnson & Apps (2009), and Schlaufman & Laughlin (2010) using a new sample of 17 binaries with precise V band photometry.

scholarly journals Effective temperature – radius relationship of M dwarfs

2019 ◽  
Vol 626 ◽  
pp. A32 ◽  
Author(s):  
S. Cassisi ◽  
M. Salaris
Keyword(s):  
Effective Temperature ◽  
Mass Star ◽  
M Dwarfs ◽  
Dwarf Stars ◽  
Fundamental Parameters ◽  
Convective Structures ◽  
Smooth Change ◽  
Theoretical Predictions ◽  
M Dwarf Stars ◽  
M Dwarf

M-dwarf stars provide very favourable conditions for finding habitable worlds beyond our solar system. The estimation of the fundamental parameters of the transiting exoplanets relies on the accuracy of the theoretical predictions for radius and effective temperature of the host M dwarf, therefore it is important to conduct multiple empirical tests of very low-mass star (VLM) models. These stars are the theoretical counterpart of M dwarfs. Recent determinations of mass, radius, and effective temperature of a sample of M dwarfs of known metallicity have disclosed an apparent discontinuity in the effective temperature-radius diagram that corresponds to a stellar mass of about 0.2 M⊙. This discontinuity has been ascribed to the transition from partially convective to fully convective stars. In this paper we compare existing VLM models to these observations, and find that theory does not predict any discontinuity at around 0.2 M⊙, but a smooth change in slope of the effective temperature-radius relationship around this mass value. The appearance of a discontinuity is due to naively fitting the empirical data with linear segments. Moreover, its origin is not related to the transition to fully convective structures. We find that this feature is instead an empirical signature for the transition to a regime where electron degeneracy provides an important contribution to the stellar equation of state, and it constitutes an additional test of the consistency of the theoretical framework for VLM models.

scholarly journals A coma-free super-high resolution optical spectrometer using 44 high dispersion sub-gratings

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Hua-Tian Tu ◽  
An-Qing Jiang ◽  
Jian-Ke Chen ◽  
Wei-Jie Lu ◽  
Kai-Yan Zang ◽  
...  
Keyword(s):  
High Resolution ◽  
Spectral Resolution ◽  
Wavelength Region ◽  
Ultra Violet ◽  
High Spectral Resolution ◽  
Visible Range ◽  
High Dispersion ◽  
Charge Coupled Device ◽  
Wide Range ◽  
High Resolution Spectrometer

AbstractUnlike the single grating Czerny–Turner configuration spectrometers, a super-high spectral resolution optical spectrometer with zero coma aberration is first experimentally demonstrated by using a compound integrated diffraction grating module consisting of 44 high dispersion sub-gratings and a two-dimensional backside-illuminated charge-coupled device array photodetector. The demonstrated super-high resolution spectrometer gives 0.005 nm (5 pm) spectral resolution in ultra-violet range and 0.01 nm spectral resolution in the visible range, as well as a uniform efficiency of diffraction in a broad 200 nm to 1000 nm wavelength region. Our new zero-off-axis spectrometer configuration has the unique merit that enables it to be used for a wide range of spectral sensing and measurement applications.

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