Abstract
Binary stars are supposed to be chemically homogeneous, as they are born from the same molecular cloud. However, high-precision chemical abundances show that some binary systems display ...chemical differences between the components, which could be due to planet engulfment. In this work, we determine precise fundamental parameters and chemical abundances for the binary system HIP 71726/HIP 71737. Our results show that the pair is truly conatal, coeval, and comoving. We also find that the component HIP 71726 is more metal-rich than HIP 71737 in the refractory elements such as iron, with ΔFe/H = 0.11 ± 0.01 dex. Moreover, HIP 71726 has a lithium abundance 1.03 dex higher than HIP 71737, which is the largest difference in Li detected in twin-star binary systems with Δ
T
eff
≤ 50 K. The ingestion of
9.8
−
1.6
+
2.0
M
⊕
of rocky material fully explains both the enhancement in refractory elements and the high Li content observed in HIP 71726, thereby reinforcing the planet-engulfment scenario in some binary systems.
Abstract
We present average magnetic field measurements derived from high-resolution near-infrared IGRINS spectra of a carefully selected sample of 28 M dwarfs. All 28 have reported magnetic field ...strengths in the literature. The main goal of this work is to investigate the accuracy, precision, and limitations of magnetic field measurements from IGRINS spectra. This investigation is critical to validating the robustness of our methods before we apply them to over 500 IGRINS-observed M dwarfs in the next paper of the series. We used the Zeeman broadening and Zeeman intensification methods to measure average magnetic fields. Our measurements are all consistent with the previous measurements to within ±1 kG, with an average offset of −0.17 kG for the broadening method and +0.19 kG for the intensification method. We find that the detection limit of IGRINS is ∼0.9 kG with the Zeeman broadening method, in accordance with the instrumental broadening limit of the spectrograph. With the Zeeman intensification method, we are able to detect down to ∼0.7 kG with a signal-to-noise ratio of 150 or greater. We find an advantage of using the intensification method over the broadening method, which is the ability to reliably measure the magnetic field strengths of stars that are cooler than 3100 K where the spectrum becomes dominated by molecular lines. Therefore, the intensification method is crucial to study stellar magnetism of late-M and brown dwarfs.
Abstract
Determining accurate effective temperatures of stars buried in the dust-obscured Galactic regions is extremely difficult from photometry. Fortunately, high-resolution infrared spectroscopy ...is a powerful tool for determining the temperatures of stars with no dependence on interstellar extinction. It has long been known that the depth ratios of temperature-sensitive and relatively insensitive spectral lines are excellent temperature indices. In this work, we provide the first extensive line depth ratio (LDR) method application in the infrared region that encompasses both the
H
and
K
bands (1.48
μ
m − 2.48
μ
m). We applied the LDR method to high-resolution (
R
≃ 45,000)
H-
and
K
-band spectra of 110 stars obtained with the Immersion Grating Infrared Spectrograph. Our sample contained stars with 3200 <
T
eff
(K) < 5500, 0.20 ≤ log
g
< 4.6, and −1.5 < M/H < 0.5. The application of this method in the
K
band yielded 21 new LDR–
T
eff
relations. We also report five new LDR–
T
eff
relations found in the
H
-band region, augmenting the relations already published by other groups. The temperatures found from our calibrations provide reliable temperatures within ∼70 K accuracy compared to spectral
T
eff
values from the literature.
Abstract
We used the Immersion GRating Infrared Spectrometer (IGRINS) to determine fundamental parameters for 61 K- and M-type young stellar objects (YSOs) located in the Ophiuchus and Upper Scorpius ...star-forming regions. We employed synthetic spectra and a Markov chain Monte Carlo approach to fit specific
K
-band spectral regions and determine the photospheric temperature (
T
), surface gravity (
log
g
), magnetic field strength (
B
), projected rotational velocity (
v
sin
i
), and
K
-band veiling (
r
K
). We determined
B
for ∼46% of our sample. Stellar parameters were compared to the results from Taurus-Auriga and the TW Hydrae association presented in Paper I of this series. We classified all the YSOs in the IGRINS survey with infrared spectral indices from Two Micron All Sky Survey and Wide-field Infrared Survey Explorer photometry between 2 and 24
μ
m. We found that Class II YSOs typically have lower
log
g
and
v
sin
i
, similar
B
, and higher
K
-band veiling than their Class III counterparts. Additionally, we determined the stellar parameters for a sample of K and M field stars also observed with IGRINS. We have identified intrinsic similarities and differences at different evolutionary stages with our homogeneous determination of stellar parameters in the IGRINS YSO survey. Considering
log
g
as a proxy for age, we found that the Ophiuchus and Taurus samples have a similar age. We also find that Upper Scorpius and TWA YSOs have similar ages, and are more evolved than Ophiuchus/Taurus YSOs.
High-resolution, near-infrared spectra will be the primary tool for finding and characterizing Earth-like planets around low-mass stars. Yet, the properties of exoplanets cannot be precisely ...determined without accurate and precise measurements of the host star. Spectra obtained with the Immersion Grating Infrared Spectrometer simultaneously provide diagnostics for most stellar parameters, but the first step in any analysis is the determination of the effective temperature. Here we report the calibration of high-resolution H-band spectra to accurately determine the effective temperature for stars between 4000 and 3000 K (∼K8-M5) using absorption line-depths of Fe i, OH, and Al i. The field star sample used here contains 254 K and M stars with temperatures derived using BT-Settl synthetic spectra. We use 106 stars with precise temperatures in the literature to calibrate our method, with typical errors of about 140 K, and systematic uncertainties less than ∼120 K. For the broadest applicability, we present Teff-line-depth-ratio relationships, which we test on 12 members of the TW Hydrae Association and at spectral resolving powers between ∼10,000 and 120,000. These ratios offer a simple but accurate measure of effective temperatures in cool stars that are distance and reddening independent.
Abstract
The fifth iteration of the Sloan Digital Sky Survey is set to obtain optical and near-infrared spectra of ∼5 million stars of all ages and masses throughout the Milky Way. As a part of these ...efforts, APOGEE and BOSS Young Star Survey (ABYSS) will observe ∼10
5
stars with ages <30 Myr that have been selected using a set of homogeneous selection functions that make use of different tracers of youth. The ABYSS targeting strategy we describe in this paper is aimed to provide the largest spectroscopic census of young stars to date. It consists of eight different types of selection criteria that take the position on the H-R diagram, infrared excess, variability, as well as the position in phase space in consideration. The resulting catalog of ∼200,000 sources (of which a half are expected to be observed) provides representative coverage of the young Galaxy, including both nearby diffuse associations as well as more distant massive complexes, reaching toward the inner Galaxy and the Galactic center.
Abstract We developed a tool that measures equivalent widths of various lines in low-resolution optical spectra, and it was applied to stellar spectra obtained as part of SDSS-V and LAMOST programs. ...These lines, such as Li i, which directly indicates stellar youth, or optical H i and Ca ii, which in emission indicate activity associated with stellar youth, are commonly seen in YSOs. We observe several notable differences in the properties of these lines between YSOs and the field stars. Using these data, we devise a set of criteria through which it is possible to confirm the youth of stars that have been observed by the ABYSS program, as well as to identify likely young stars that have serendipitously been observed by other programs. We examine the decrement of H lines seen in emission in CTTSs, and estimate the properties of the accretion stream that is responsible for the production of these lines. Finally, we examine the evolution of Li i as a function of age, and characterize the scatter in its abundance that appears to be intrinsic in young M dwarfs.
Abstract We developed a grid of stellar rotation models for low-mass and solar-type classical T Tauri stars (CTTS; 0.3 M ⊙ < M * < 1.2 M ⊙ ). These models incorporate the star–disk interaction and ...magnetospheric ejections to investigate the evolution of the stellar rotation rate as a function of the mass of the star M * , the magnetic field ( B * ), and stellar wind ( M ̇ wind ). We compiled and determined stellar parameters for 208 CTTS, such as projected rotational velocity v sin ( i ) , mass accretion rate M ̇ acc , stellar mass M * , ages, and estimated rotational periods using Transiting Exoplanet Survey Satellite (TESS) data. We also estimated a representative value of the mass-loss rate for our sample using the O i λ 6300 spectral line. Our results confirm that v sin ( i ) measurements in CTTS agree with the rotation rates provided by our spin models in the accretion-powered stellar winds picture. In addition, we used the approximate Bayesian computation technique to explore the connection between the model parameters and the observational properties of CTTS. We find that the evolution of v sin ( i ) with age might be regulated by variations in (1) the intensity of B * and (2) the fraction of the accretion flow ejected in magnetic winds, removing angular momentum from these systems. The youngest stars in our sample (∼1 Myr) show a median branching ratio M ̇ wind / M ̇ acc ∼ 0.16 and median B * ∼ 2000 G, in contrast to ∼0.01 and 1000 G, respectively, for stars with ages ≳3 Myr.
We present a high-resolution (∼0 12, ∼16 au, mean sensitivity of 50 Jy beam−1 at 225 GHz) snapshot survey of 32 protoplanetary disks around young stars with spectral type earlier than M3 in the ...Taurus star-forming region using the Atacama Large Millimeter Array. This sample includes most mid-infrared excess members that were not previously imaged at high spatial resolution, excluding close binaries and objects with high extinction, thereby providing a more representative look at disk properties at 1-2 Myr. Our 1.3 mm continuum maps reveal 12 disks with prominent dust gaps and rings, 2 of which are around primary stars in wide binaries, and 20 disks with no resolved features at the observed resolution (hereafter smooth disks), 8 of which are around the primary star in wide binaries. The smooth disks were classified based on their lack of resolved substructures, but their most prominent property is that they are all compact with small effective emission radii (Reff,95% 50 au). In contrast, all disks with Reff,95% of at least 55 au in our sample show detectable substructures. Nevertheless, their inner emission cores (inside the resolved gaps) have similar peak brightness, power-law profiles, and transition radii to the compact smooth disks, so the primary difference between these two categories is the lack of outer substructures in the latter. These compact disks may lose their outer disk through fast radial drift without dust trapping, or they might be born with small sizes. The compact dust disks, as well as the inner disk cores of extended ring disks, that look smooth at the current resolution will likely show small-scale or low-contrast substructures at higher resolution. The correlation between disk size and disk luminosity correlation demonstrates that some of the compact disks are optically thick at millimeter wavelengths.
Abstract
We present measurements of the
H-
and
K
-band veiling for 141 young stellar objects (YSOs) in the Taurus-Auriga star-forming region using high-resolution spectra from the Immersion Grating ...Near-Infrared Spectrometer. In addition to providing measurements of
r
H
and
r
K
, we produce low-resolution spectra of the excess emission across the
H
and
K
bands. We fit temperatures to the excess spectra of 46 members of our sample and measure near-infrared excess temperatures ranging from 1200–2200 K, with an average of 1575 ± 225 K. We compare the luminosity of the excess continuum emission in Class II and Class III YSOs and find that a number of Class III sources display a significant amount of excess flux in the near-infrared. We conclude that the mid-infrared SED slope, and therefore young stellar object classification, is a poor predictor of the amount of near-infrared veiling. If the veiling arises in thermal emission from dust, its presence implies a significant amount of remaining inner-disk (<1 au) material in these Class III sources. We also discuss the possibility that the veiling effects could result from massive photospheric spots, unresolved binary companions, or accretion emission. Six low-mass members of our sample contain a prominent feature in their
H
-band excess spectra that is consistent with veiling from cool photospheric spots.
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