Due to their ubiquity and very long main-sequence lifetimes, M dwarfs provide an excellent tool to study the formation and chemical enrichment history of our Galaxy. However, owing to their intrinsic ...faintness, the acquisition of high-resolution, high signal-to-noise spectra of low-mass stars has been limited to small numbers of very nearby stars, mostly from the Galactic disk population. On the other hand, large numbers of low- to medium-resolution spectra of M-type dwarf stars from both the local Galactic disk and halo are available from various surveys. In order to fully exploit these data, we develop a template-fit method using a set of empirically assembled M dwarf/subdwarf classification templates, based on the measurements of the TiO and CaH molecular bands near 7000 , which are used to classify M dwarfs/subdwarfs by spectral type and metallicity class. We further present a pipeline to automatically determine the effective temperature Teff, metallicity M/H, -element to iron abundance ratio /Fe, and surface gravity log g of M dwarfs/subdwarfs using the latest version of BT-Settl model atmospheres. We apply these methods to a set of low- to medium-resolution spectra of 1544 high proper-motion ( ≥ 0 4 yr−1) M dwarfs/subdwarfs, collected at the MDM observatory, Lick Observatory, Kitt-Peak National Observatory, and Cerro-Tololo Interamerican Observatory. Our metallicity estimates appear to be consistent with the expected color-magnitude variation of stars relative to the atmospheric composition, as our sample shows a clear stratification with respect to metallicity in the Hertzsprung-Russel diagram constructed from their Gaia DR2 parallaxes and optical magnitudes. Furthermore, the measured chemical parameters of the two components in 48 binary systems are in good agreement with each other, which suggest a precision of 0.22 dex in M/H, 0.08 dex in /Fe, and 0.16 dex in the combined index /Fe + M/H. We find that the relationship between color and spectral subtype depends on metallicity class, as the color GBP − GRP is more sensitive to subtype for metal-rich M dwarfs in comparison to metal-poor M subdwarfs. We also demonstrate that effective temperature as a function of spectral subtype has a steeper slope for metal-rich M dwarfs than metal-poor M subdwarfs. There is also a good consistency between "metallicity class," obtained from the empirical classification templates, and the index /Fe + M/H (∼ /H), obtained from BT-Settl model fitting, which means that the more easily measured "metallicity class" can be used as a relatively reliable indicator of absolute -element abundance, /H, in low-mass stars. Finally, we examine the distribution of our stars in the /Fe versus M/H diagram, which shows evidence of clustering in chemical abundance makeup, suggestive of discrete populations among the local disk and halo stars. We predict that analyses of larger samples of spectra of nearby M-type stars will uncover a complex structure of our Galaxy.
Abstract We present the first elemental abundance measurements of the K dwarf (K7V) exoplanet-host star WASP-107 using high-resolution ( R ≃45,000), near-infrared ( H - and K -band) spectra taken ...from Gemini-S/IGRINS. We use the previously determined physical parameters of the star from the literature and infer the abundances of 15 elements—C, N, O, Na, Mg, Al, Si, K, Ca, Ti, V, Cr, Mn, Fe, and Ni, all with precision < 0.1 dex—based on model fitting using MARCS model atmospheres and the Turbospectrum spectral synthesis code. Our results show near-solar abundances and a carbon-to-oxygen ratio (C/O) of 0.50 ± 0.10, which is consistent with the solar value of 0.54 ± 0.09. The orbiting planet, WASP-107b, is a super-Neptune with a mass in the Neptune regime (=1.8 M Nep ) and a radius close to Jupiter's (=0.94 R Jup ). This planet is also being targeted by four JWST Cycle 1 programs in transit and eclipse, which should provide highly precise measurements of atmospheric abundances. This will enable us to properly compare the planetary and stellar chemical abundances, which is essential in understanding the formation mechanisms, internal structure, and chemical composition of exoplanets. Our study is a proof-of-concept that will pave the way for such measurements to be made for all of JWST’s cooler exoplanet-host stars.
Abstract
To understand the parameter degeneracy of M subdwarf spectra at low resolution, we assemble a large number of spectral features in the wavelength range 0.6–2.5
μ
m with band strength ...quantified by narrowband indices. Based on the index trends of BT-Settl model sequences, we illustrate how the main atmospheric parameters (
T
eff
, log
g
, M/H, and
α
/Fe) affect each spectral feature differently. Furthermore, we propose a four-step process to determine the four parameters sequentially, which extends the basic idea proposed by Jao et al. Each step contains several spectral features that break the degeneracy effect when determining a specific stellar parameter. Finally, the feasibility of each spectroscopic diagnostic with different spectral quality is investigated. The result is resolution-independent down to
R
∼ 200.
Abstract
We present a model-fit pipeline to determine the stellar parameters of M-type dwarfs, which is an improvement on our previous work described in Hejazi et al. We apply this pipeline to ...analyze the low-resolution (
R
∼ 2000) spectra of 3745 M dwarfs/subdwarfs, collected at the MDM Observatory, Lick Observatory, Kitt Peak National Observatory, and Cerro Tololo Inter-American Observatory. We examine the variation of the inferred parameter values in the H-R diagram constructed from their Gaia Early Data Release 3 (EDR3) parallaxes and optical magnitudes. We also study the distribution of our stars in the abundance diagram of
α
/Fe versus M/H and inspect the variation of their metallicity class, effective temperature, and surface gravity, as well as their Galactic velocity components
U
,
V
, and
W
, in this diagram. In addition, the analyses of the stars’ projected motions in the two-dimensional
UV
,
VW
, and
UW
planes, the variation of their chemical parameters in these planes, and their distribution in the abundance−velocity diagrams are important parts of this study. The precision of our model-fit pipeline is confirmed by the clear stratification of effective temperature and chemical parameters in the H-R diagram; the similarity of the stars’ distribution in the
α
/Fe versus M/H diagram and in the metallicity−velocity planes to those from other studies; the revealing of substructure in the abundance−velocity diagrams; and chemical homogeneity between the components of a set of binary systems.
Abstract
In this research note, we present
linemake
, an open-source atomic and molecular line list generator. Rather than a replacement for a number of well-established atomic and molecular spectral ...databases,
linemake
aims to be a lightweight, easy-to-use tool to generate formatted and curated lists suitable for spectral synthesis work. We encourage users of
linemake
to understand the sources of their transition data and cite them as appropriate in published work. We provide the code, line database, and an extensive list of literature references in a
GitHub
repository (
https://github.com/vmplacco/linemake
), which will be updated regularly as new data become available.
We present a model-fit pipeline to determine the stellar parameters of M-type dwarfs, which is an improvement upon our previous work described in Hejazi et al. 2020. We apply this pipeline to analyze ...the low-resolution (R~2000) spectra of 3745 M dwarfs/subdwarfs, collected at the MDM Observatory, Lick Observatory, Kitt Peak National Observatory, and Cerro Tololo Interamerican Observatory. We examine the variation of the inferred parameter values in the HR diagram constructed from their Gaia Early Data Release 3 (EDR3) parallaxes and optical magnitudes. We also study the distribution of our stars in the abundance diagram of alpha/Fe versus M/H and inspect the variation of their metallicity class, effective temperature, and surface gravity as well as their Galactic velocity components U, V, and W in this diagram. In addition, the analyses of the stars' projected motions in the two-dimensional UV, VW, and UW planes and the variation of their chemical parameters in these planes, and also their distribution in the abundance-velocity diagrams are important parts of this study. The precision of our model-fit pipeline is confirmed by the clear stratification of effective temperature and chemical parameters in the HR diagram, the similarity of the stars' distribution in the alpha/Fe versus M/H diagram and in the metallicity-velocity planes with those from other studies, revealing substructure in the abundance-velocity diagrams, and chemical homogeneity between the components of a set of binary systems.
Exoplanets hosting M dwarfs are the best targets to characterize Earth-like or super-Earth planetary atmospheres with the James Webb Space Telescope (JWST). We determine detailed stellar parameters ...(\(T_{\rm eff}\), log\(g\), and \(\xi\)) and individual abundances of twelve elements for four cool M dwarfs hosting exoplanets TOI-1685, GJ 436, GJ 3470, and TOI-2445, scheduled for future observations by the JWST. The analysis utilizes high-resolution near-infrared spectra from the SDSS-IV APOGEE survey between 1.51-1.69\(\mu\). Based on 1D-LTE plane-parallel models, we find that TOI-2445 is slightly metal-poor (Fe/H = -0.16\(\pm\)0.09), while TOI-1685, GJ 436 and GJ 3470 are more metal-rich (Fe/H = 0.06\(\pm\)0.18, 0.10\(\pm\)0.20 dex, 0.25\(\pm\)0.15). The derived C/O ratios for TOI-2445, TOI-1685, GJ 436, and GJ 3470 are 0.526\(\pm\)0.027, 0.558\(\pm\)0.097, 0.561\(\pm\)0.029, and 0.638\(\pm\)0.015, respectively. From results for 28 M dwarfs analyzed homogeneously from APOGEE spectra, we find exoplanet-hosting M dwarfs exhibit a C/O abundance ratio approximately 0.01 to 0.05 higher than those with non-detected exoplanets, at limits of a statistically significant offset. A linear regression of Fe/H \textit{vs.} C/O distribution reveals a noticeable difference in the angular coefficient between FGK dwarfs (0.27) and M dwarfs (0.13). Assuming our abundance ratios of Ca/Mg, Si/Mg, Al/Mg, and Fe/Mg, we determine a mass of 3.276$^{+0.448}_{-0.419}$$M_{\oplus}\( for TOI-2445 b, having density (6.793\)^{+0.005}_{-0.099}\( g.cm\)^{-3}\() and core mass fraction (0.329\)_{-0.049}^{+0.028}\() very similar to Earth's. We also present an atlas of 113 well-defined spectral lines to analyze M dwarfs in the \)H$-band and a comprehensive evaluation of uncertainties from variations in the atmospheric parameters, signal-to-noise, and pseudo-continuum.
We present the first elemental abundance measurements of the K dwarf (K7V) exoplanet-host star WASP-107 using high-resolution (R = 45,000), near-infrared (H- and K-band) spectra taken from ...Gemini-S/IGRINS. We use the previously determined physical parameters of the star from the literature and infer the abundances of 15 elements: C, N, O, Na, Mg, Al, Si, K, Ca, Ti, V, Cr, Mn, Fe, and Ni, all with precision < 0.1 dex, based on model fitting using MARCS model atmospheres and the spectral synthesis code Turbospectrum. Our results show near-solar abundances and a carbon-to-oxygen ratio (C/O) of 0.50 (+/-0.10), consistent with the solar value of 0.54 (+/-0.09). The orbiting planet, WASP-107b, is a super Neptune with a mass in the Neptune regime (= 1.8 M_Nep) and a radius close to Jupiter's (= 0.94 R_Jup). This planet is also being targeted by four JWST Cycle 1 programs in transit and eclipse, which should provide highly precise measurements of atmospheric abundances. This will enable us to properly compare the planetary and stellar chemical abundances, which is essential in understanding the formation mechanisms, internal structure, and chemical composition of exoplanets. Our study is a proof-of-concept that will pave the way for such measurements to be made for all JWST's cooler exoplanet-host stars.
To understand the parameter degeneracy of M subdwarf spectra at low resolution, we assemble a large number of spectral features in the wavelength range of 0.6-2.5 {\mu}m with band strength quantified ...by narrowband indices. Based on the index trends of BT-Settl model sequences, we illustrate how the main atmospheric parameters (Teff, log g, M/H, and alpha/Fe) affect each spectral feature differently. Furthermore, we propose a four-step process to determine the four parameters sequentially, which extends the basic idea proposed by Jao et al. Each step contains several spectral features that break the degeneracy effect when determining a specific stellar parameter. Finally, the feasibility of each spectroscopic diagnostic with different spectral qualities is investigated. The result is resolution-independent down to R~200.
Using Keck Planet Imager and Characterizer (KPIC) high-resolution ($R$~35000)
spectroscopy from 2.29-2.49 $\mu$m, we present uniform atmospheric retrievals
for eight young substellar companions with ...masses of ~10-30 $M_\textrm{Jup}$,
orbital separations spanning ~50-360 au, and $T_\textrm{eff}$ between
~1500-2600 K. We find that all companions have solar C/O ratios, and
metallicities, to within the 1-2$\sigma$ level, with the measurements clustered
around solar composition. Stars in the same stellar associations as our systems
have near-solar abundances, so these results indicate that this population of
companions is consistent with formation via direct gravitational collapse.
Alternatively, core accretion outside the CO snowline would be compatible with
our measurements, though the high mass ratios of most systems would require
rapid core assembly and gas accretion in massive disks. On a population level,
our findings can be contrasted with abundance measurements for directly imaged
planets with m<10 $M_\textrm{Jup}$, which show tentative atmospheric metal
enrichment. In addition, the atmospheric compositions of our sample of
companions are distinct from those of hot Jupiters, which most likely form via
core accretion. For two companions with $T_\textrm{eff}$~1700-2000 K (kap And b
and GSC 6214-210 b), our best-fit models prefer a non-gray cloud model with
>3$\sigma$ significance. The cloudy models yield 2-3$\sigma$ lower
$T_\textrm{eff}$ for these companions, though the C/O and C/H still agree
between cloudy and clear models at the $1\sigma$ level. Finally, we constrain
12CO/13CO for three companions with the highest S/N data (GQ Lup b, HIP 79098
b, and DH Tau b), and report $v$sin($i$) and radial velocities for all
companions.
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