High-resolution Near-infrared Spectra Research Articles

Stellar Characterization and Chemical Abundances of Exoplanet-hosting M Dwarfs from APOGEE Spectra: Future JWST Targets

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 eff, logg, and ξ) and individual abundances of 12 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 Sloan Digital Sky Survey IV APOGEE survey between 1.51 and 1.69 μm. Based on 1D LTE plane-parallel models, we find that TOI-2445 is slightly metal poor ([Fe/H] = −0.16 ± 0.09 dex), while TOI-1685, GJ 436, and GJ 3470 are more metal rich ([Fe/H] = 0.06 ± 0.18, 0.10 ± 0.20, and 0.25 ± 0.15 dex, respectively). The derived C/O ratios for TOI-2445, TOI-1685, GJ 436, and GJ 3470 are 0.526 ± 0.027, 0.558 ± 0.097, 0.561 ± 0.029, and 0.638 ± 0.015, respectively. From the results for 28 M dwarfs analyzed homogeneously from Apache Point Observatory Galactic Evolution Experiment (APOGEE) spectra, we find exoplanet-hosting M dwarfs exhibit a C/O abundance ratio approximately 0.01–0.05 higher than those with nondetected exoplanets, at limits of a statistically significant offset. A linear regression of the [Fe/H] versus 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 3.276−0.419+0.448 M ⊕ for TOI-2445 b, which has a density (6.793 −0.099+0.005 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 ratio, and pseudocontinuum.

Comprehensive High-resolution Chemical Spectroscopy of Barnard’s Star with SPIRou

Determination of fundamental parameters of stars impacts all fields of astrophysics, from galaxy evolution to constraining the internal structure of exoplanets. This paper presents a detailed spectroscopic analysis of Barnard’s star (otherwise known as Gl 699) that compares an exceptionally high-quality (an average signal-to-noise ratio of ∼1000 in the entire domain), high-resolution near-infrared (NIR) spectrum taken with Canada-France-Hawaii Telescope/SPIRou to PHOENIX-ACES stellar atmosphere models. The observed spectrum shows thousands of lines not identified in the models with a similarly large number of lines present in the model but not in the observed data. We also identify several other caveats, such as continuum mismatch, unresolved contamination, and spectral lines significantly shifted from their expected wavelengths; all of these can be a source of bias for the determination of abundance. Out of >104 observed lines in the NIR that could be used for chemical spectroscopy, we identify a short list of a few hundred lines that are reliable. We present a novel method for determining the effective temperature (T eff) and overall metallicity of slowly rotating M dwarfs that uses several groups of lines as opposed to bulk spectral fitting methods. With this method, we infer T eff = 3231 ± 21 K for Barnard's star, consistent with the value of 3238 ± 11 K inferred from the interferometric method. We also provide measurements of the abundance of 15 different elements for Barnard's star, including the abundances of four elements (K, O, Y, Th) never reported before for this star. This work emphasizes the need to improve current atmosphere models to fully exploit the NIR domain for chemical spectroscopy analysis.

Is the RSGC4 (Alicante 8) Cluster a Real Star Cluster? Peculiar Radial Velocities of Red Supergiant Stars

Young massive star clusters, like the six red supergiant clusters in the Scutum complex, provide valuable insights into star formation and galaxy structures. We investigated the high-resolution near-infrared spectra of 60 RSG candidates in these clusters using the Immersion Grating Infrared Spectrograph. Among the candidates in RSGC4, we found significant scattering in radial velocity (−64 to 115 km s−1), unlike other clusters with velocities of ∼100 km s−1. Most candidates in RSGC4 have Q GK s values larger than 1.7, suggesting that they could be early AGB stars. Four candidates in RSGC4 exhibit infrared excess and distinct absorption features absent in other candidates. Two of these stars exhibit absorption lines resembling those of D-type symbiotic stars, showing radial velocity changes in multiepoch observations. Analysis of relative proper motions revealed no runaway/walkaway stars in RSGC4. The dynamic properties of RSGC4 and RSGC1 differ from the disklike motions of other clusters: RSGC4 has low normalized horizontal action J hor = J ϕ /J tot and vertical action J ver = (J z − J R)/J tot values and high eccentricities, while RSGC1 has vertical motions with high J ver values and inclinations. We propose that RSGC4 may not be a genuine star cluster but rather a composite of RSGs and AGB stars distributed along the line of sight at similar distances, possibly originating from various environments. Our results suggest a complex and hierarchical secular evolution of star clusters in the Scutum complex, emphasizing the importance of considering factors beyond density crowding when identifying star clusters in the bulge regions.

M giants with IGRINS

Context. To be able to investigate the chemical history of the entire Milky Way, it is imperative to also study its dust-obscured regions in detail, as this is where most of the mass lies. The Galactic Center is an example of such a region. Due to the intervening dust along the line of sight, near-infrared spectroscopic investigations are necessary to study this region of interest. Aims. The aim of this work is to demonstrate that M giants observed at high spectral resolution in the H- and K-bands (1.5–2.4 μm) can yield useful abundance ratio trends versus metallicity for 21 elements. These elements can then also be studied for heavily dust-obscured regions of the Galaxy, such as the Galactic Center. The abundance ratio trends will be important for further investigation of the Galactic chemical evolution in these regions. Methods. We observed near-infrared spectra of 50 M giants in the solar neighborhood at high signal-to-noise and at a high spectral resolution with the IGRINS spectrometer on the Gemini South telescope. The full H- and K-bands were recorded simultaneously at R = 45 000. Using a manual spectral synthesis method, we determined the fundamental stellar parameters for these stars and derived the stellar abundances for 21 atomic elements, namely, F, Mg, Si, S, Ca, Na, Al, K, Sc, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Y, Ce, Nd, and Yb. We systematically studied useful spectral lines of all these elements in the H- and K-bands. Results. We demonstrate that elements can be analyzed from H- and K-band high-resolution spectra, and we show which spectral lines can be used for an abundance analysis, identifying them line by line. We discuss the 21 abundance ratio trends and compare them with those determined from APOGEE and from the optical Giants in the Local Disk (GILD) sample. From high-resolution H- and K-band spectra, the trends of the heavy elements Cu, Zn, Y, Ce, Nd, and Yb can be retrieved. This opens up the nucleosynthetic channels, including the s-process and the r-process in dust-obscured populations. The [Mn/Fe] versus [Fe/H] trend is shown to be more or less flat at low metallicities, implying that existing non-local thermodynamic equilibrium correction is relevant. Conclusions. With high-resolution near-infrared spectra, it is possible to determine reliable abundance ratio trends versus metallicity for 21 elements, including elements formed in several different nucleosynthetic channels. It is also possible to determine the important neutron-capture elements, both s- and r-dominated elements. This opens up the possibility to study the chemical evolution in detail of dust-obscured regions of the Milky Way, such as the Galactic Center. The M giants are useful bright probes for these regions and for future studies of extra-galactic stellar populations. A careful analysis of high-quality spectra is needed to retrieve all of these elements, which are often from weak and blended lines. A spectral resolution of R ≳ 40 000 is a further quality that helps in deriving precise abundances for this range of elements. In comparison to APOGEE, we can readily obtain the abundances for Cu, Ce, Nd, and Yb from the H-band, demonstrating an advantage of analyzing high-resolution spectra.

Stellar Population Astrophysics (SPA) with TNG

Context. The age, evolution, and chemical properties of the Galactic disk can be effectively ascertained using open clusters. Within the large program Stellar Populations Astrophysics at the Telescopio Nazionale Galileo, we specifically focused on stars in open clusters, to investigate various astrophysical topics, from the chemical content of very young systems to the abundance patterns of lesser studied intermediate-age and old open clusters. Aims. We investigate the astrophysically interesting element fluorine (F), which has an uncertain and intriguing cosmic origin. We also determine the abundance of cerium (Ce), as F abundance is expected to correlate with the s-process elements. We intend to determine the trend of F abundance across the Galactic disk as a function of metallicity and age. This will offer insights into Galactic chemical evolution models, potentially enhancing our comprehension of this element’s cosmic origin. Methods. High-resolution near-infrared spectra were obtained using the GIANO-B spectrograph. The Python version of Spectroscopy Made Easy (PySME), was used to derive atmospheric parameters and abundances. The stellar parameters were determined using OH, CN, and CO molecular lines along with Fe I lines. The F and Ce abundances were inferred using two K-band HF lines (λλ 2.28, 2.33 µm) and two atomic H-band lines (λλ 1.66, and 1.71 µm), respectively. Results. Of all the clusters in our sample, only King 11 had not been previously studied through medium- to high-resolution spectroscopy, and our stellar parameter and metallicity findings align well with those documented in the literature. We have successfully inferred F and Ce abundances in all seven open clusters and probed the radial and age distributions of abundance ratios. This paper presents the first F Galactic radial abundance gradient. Our results are also compared with literature estimates and with Galactic chemical evolution models that have been generated using different F production channels. Conclusions. Our results indicate a constant, solar pattern in the [F/Fe] ratios across clusters of different ages, supporting the latest findings that fluorine levels do not exhibit any secondary behavior for stars with solar or above-solar metallicity. However, an exception to this trend is seen in NGC 6791, a metal-rich, ancient cluster whose chemical composition is distinct due to its enhanced fluorine abundance. This anomaly strengthens the hypothesis that NGC 6791 originated in the inner regions of the Galaxy before migrating to its present position. By comparing our sample stars with the predictions of Galactic chemical evolution models, we came to the conclusion that both asymptotic giant branch stars and massive stars, including a fraction of fast rotators that increase with decreasing metallicity, are needed to explain the cosmic origin of F.

CAPOS: the bulge Cluster APOgee Survey IV elemental abundances of the bulge globular cluster NGC 6558

ABSTRACT This study presents the results concerning six red giant stars members of the globular cluster NGC 6558. Our analysis utilized high-resolution near-infrared spectra obtained through the CAPOS initiative (the APOgee Survey of Clusters in the Galactic Bulge), which focuses on surveying clusters within the Galactic Bulge, as a component of the Apache Point Observatory Galactic Evolution Experiment II survey (APOGEE-2). We employ the Brussels Automatic Code for Characterizing High accUracy Spectra (BACCHUS) code to provide line-by-line elemental-abundances for Fe-peak (Fe, Ni), α-(O, Mg, Si, Ca, Ti), light-(C, N), odd-Z (Al), and the s-process element (Ce) for the four stars with high-signal-to-noise ratios. This is the first reliable measure of the CNO abundances for NGC 6558. Our analysis yields a mean metallicity for NGC 6558 of 〈[Fe/H]〉 = −1.15 ± 0.08, with no evidence for a metallicity spread. We find a Solar Ni abundance, 〈[Ni/Fe]〉 ∼ +0.01, and a moderate enhancement of α-elements, ranging between +0.16 and <+0.42, and a slight enhancement of the s-process element 〈[Ce/Fe]〉 ∼ +0.19. We also found low levels of 〈[Al/Fe]〉 ∼ +0.09, but with a strong enrichment of nitrogen, [N/Fe] > +0.99, along with a low level of carbon, [C/Fe] < −0.12. This behaviour of Nitrogen-Carbon is a typical chemical signature for the presence of multiple stellar populations in virtually all GCs; this is the first time that it is reported in NGC 6558. We also observed a remarkable consistency in the behaviour of all the chemical species compared to the other CAPOS bulge GCs of the same metallicity.

M67 Blue Stragglers with High-resolution Infrared Spectroscopy

We report on the first detailed infrared chemical analysis of five binary members (S277, S997, S975, S1031, and S1195) in the open cluster M67 (NGC 2682). These stars are located outside (bluer and/or brighter than) the main-sequence turnoff region in M67. High-resolution (R ∼ 45,000) near-infrared spectra were obtained with the Immersion GRating INfrared Spectrograph (IGRINS) at the McDonald Observatory 2.7 m Harlan J. Smith Telescope, providing full spectral coverage of the H and K bands. The abundances of C, Na, Mg, Al, Si, S, Ca, Fe, and Ni are measured using neutral atomic absorption lines. We detect v sin i ≥ 25 km s−1 in three of our program stars: S1031, S975, and S1195. We find our derived abundances to be in good agreement with turnoff star abundances, similar to published analyses of blue straggler stars in M67 from optical spectra. Detection of a carbon enhancement or depletion resulting from mass transfer is difficult due to the uncertainties in the carbon abundance and the relatively modest changes that may occur through red giant and asymptotic giant branch evolution.

Magnetic Field Measurements of Low-mass Stars from High-resolution Near-infrared IGRINS Spectra

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.

Silicon and strontium abundances of very metal-poor stars determined from near-infrared spectra

Abstract Silicon and strontium are key elements to explore the nucleosynthesis and chemical evolution of the Galaxy by measurements of very metal-poor stars. There are, however, only a few useful spectral lines of these elements in the optical range that are measurable for such low-metallicity stars. Here we report on abundances of these two elements determined from near-infrared high-resolution spectra obtained with the Subaru Telescope Infrared Doppler instrument. Si abundances are determined for as many as 26 Si lines for six very and extremely metal-poor stars (−4.0 < [Fe/H] < −1.5), which significantly improves the reliability of the abundance measurements. All six stars, including three carbon-enhanced objects, show over-abundances of Si ([Si/Fe] ∼ +0.5). Two stars with [Fe/H] ∼ −1.5 have relatively small over-abundances. The [Mg/Si] ratios agree with the solar value, except for one metal-poor star with carbon excess. Strontium abundances are determined from the triplet lines for four stars, including two for the first time. The consistency of the Sr abundances determined from near-infrared and optical spectra require further examination from additional observations.

CAPOS: The bulge Cluster APOgee Survey

We performed the first detailed spectral analysis of red giant members of the relatively high-metallicity globular cluster (GC) Tononzintla 2 (Ton 2) using high-resolution near-infrared spectra collected with the Apache Point Observatory Galactic Evolution Experiment II survey (APOGEE-2), obtained as part of the bulge Cluster APOgee Survey. We investigated chemical abundances for a variety of species including the light, odd-Z, α-, Fe-peak, and neutron-capture elements from high S/N spectra of seven giant members. The derived mean cluster metallicity is [Fe/H] = −0.70 ± 0.05, with no evidence for an intrinsic metallicity spread. Ton 2 exhibits a typical α-enrichment that follows the trend for high-metallicity Galactic GCs, similar to that seen in 47 Tucanae and NGC 6380. We find a significant nitrogen spread (> 0.87 dex), and a large fraction of nitrogen-enriched stars that populate the cluster. Given the relatively high-metallicity of Ton 2, these nitrogen-enriched stars are well above the typical Galactic levels, indicating the prevalence of the multiple-population phenomenon in this cluster that also contains several stars with typical low first-generation N abundances. We also identify the presence of [Ce/Fe] abundance spread in Ton 2, which is correlated with the nitrogen enhancement, indicating that the s-process enrichment in this cluster has likely been produced by relatively low-mass asymptotic giant branch stars. Furthermore, we find a mean radial velocity of the cluster, −178.6 ± 0.86 km s−1, with a small velocity dispersion, 2.99 ± 0.61 km s−1, which is typical of GCs. We also find a prograde bulge-like orbit for Ton 2 that appears to be radial and highly eccentric. Finally, the considerably nitrogen-enhanced population observed in Ton 2, combined with its dynamical properties, makes this object a potential progenitor for the nitrogen-enriched field stars identified so far toward the bulge region at similar metallicity.

Elemental Abundances of nearby M Dwarfs Based on High-resolution Near-infrared Spectra Obtained by the Subaru/IRD Survey: Proof of Concept

Abstract Detailed chemical analyses of M dwarfs are scarce but necessary to constrain the formation environment and internal structure of planets being found around them. We present elemental abundances of 13 M dwarfs (2900 < T eff < 3500 K) observed in the Subaru/IRD planet search project. They are mid- to late-M dwarfs whose abundance of individual elements has not been well studied. We use the high-resolution (∼70,000) near-infrared (970–1750 nm) spectra to measure the abundances of Na, Mg, Si, K, Ca, Ti, V, Cr, Mn, Fe, and Sr by the line-by-line analysis based on model atmospheres, with typical errors ranging from 0.2 dex for [Fe/H] to 0.3–0.4 dex for other [X/H]. We measure radial velocities from the spectra and combine them with Gaia astrometry to calculate the Galactocentric space velocities UVW. The resulting [Fe/H] values agree with previous estimates based on medium-resolution K-band spectroscopy, showing a wide distribution of metallicity (−0.6 < [Fe/H] < +0.4). The abundance ratios of individual elements [X/Fe] are generally aligned with the solar values in all targets. While the [X/Fe] distributions are comparable to those of nearby FGK stars, most of which belong to the thin-disk population, the most metal-poor object, GJ 699, could be a thick-disk star. The UVW velocities also support this. The results raise the prospect that near-infrared spectra of M dwarfs obtained in the planet search projects can be used to grasp the trend of elemental abundances and the Galactic stellar population of nearby M dwarfs.

Observationally Constraining the Starspot Properties of Magnetically Active M67 Sub-subgiant S1063

Abstract Our understanding of the impact of magnetic activity on stellar evolution continues to unfold. This impact is seen in sub-subgiant stars, defined to be stars that sit below the subgiant branch and red of the main sequence in a cluster color–magnitude diagram. Here we focus on S1063, a prototypical sub-subgiant in open cluster M67. We use a novel technique combining a two-temperature spectral decomposition and light-curve analysis to constrain starspot properties over a multiyear time frame. Using a high-resolution near-infrared IGRINS spectrum and photometric data from K2 and ASAS-SN, we find a projected spot filling factor of 32% ± 7% with a spot temperature of 4000 ± 200 K. This value anchors the variability seen in the light curve, indicating the spot filling factor of S1063 ranged from 20% to 45% over a four-year time period with an average spot filling factor of 30%. These values are generally lower than those determined from photometric model comparisons but still indicate that S1063, and likely other sub-subgiants, are magnetically active spotted stars. We find observational and theoretical comparisons of spotted stars are nuanced due to the projected spot coverage impacting estimates of the surface-averaged effective temperature. The starspot properties found here are similar to those found in RS CVn systems, supporting classifying sub-subgiants as another type of active giant star binary system. This technique opens the possibility of characterizing the surface conditions of many more spotted stars than previous methods, allowing for larger future studies to test theoretical models of magnetically active stars.

Fiber Fabry-Perot astrophotonic correlation spectroscopy for remote gas identification and radial velocity measurements.

We present a novel, to the best of our knowledge, remote gas detection and identification technique based on correlation spectroscopy with a piezoelectric tunable fiber-optic Fabry-Perot filter. We show that the spectral correlation amplitude between the filter transmission window and gas absorption features is related to the gas absorption optical depth, and that different gases can be distinguished from one another using their correlation signal phase. Using a previously captured telluric-corrected high-resolution near-infrared spectrum of Venus, we show that the radial velocity of Venus can be extracted from the phase of higher order harmonic lock-in signals. This correlation spectroscopy technique has applications in the detection and radial velocity determination of weak spectral features in astronomy and remote sensing. We experimentally demonstrate a remote CO2 detection system using a lock-in amplifier, fiber-optic Fabry-Perot filter, and single channel avalanche photodiode.

The IGRINS YSO Survey. I. Stellar Parameters of Pre-main-sequence Stars in Taurus-Auriga

Abstract We present fundamental parameters for 110 canonical K- and M-type (1.3−0.13 M ⊙) Taurus-Auriga young stellar objects (YSOs). The analysis produces a simultaneous determination of effective temperature (T eff), surface gravity (log g), magnetic-field strength (B), and projected rotational velocity ( v sin i ). Our method employed synthetic spectra and high-resolution (R ∼ 45,000) near-infrared spectra taken with the Immersion GRating INfrared Spectrometer (IGRINS) to fit specific K-band spectral regions most sensitive to those parameters. The use of these high-resolution spectra reduces the influence of distance uncertainties, reddening, and non-photospheric continuum emission on the parameter determinations. The median total (fit + systematic) uncertainties were 170 K, 0.28 dex, 0.60 kG, 2.5 km s−1 for T eff, log g, B, and v sin i , respectively. We determined B for 41 Taurus YSOs (upper limits for the remainder) and find systematic offsets (lower T eff, higher log g and v sin i ) in parameters when B is measurable but not considered in the fit. The average log g for the Class ii and Class iii objects differs by 0.23 ± 0.05 dex, which is consistent with Class iii objects being the more evolved members of the star-forming region. However, the dispersion in log g is greater than the uncertainties, which highlights how the YSO classification correlates with age (log g), yet there are exceptionally young (lower log g) Class iii YSOs and relatively old (higher log g) Class ii YSOs with unexplained evolutionary histories. The spectra from this work are provided in an online repository along with TW Hydrae Association comparison objects and the model grid used in our analysis.

A Near-infrared Chemical Inventory of the Atmosphere of 55 Cancri e

Abstract We present high-resolution near-infrared spectra taken during eight transits of 55 Cancri e, a nearby low-density super-Earth with a short orbital period (<18 hr). While this exoplanet’s bulk density indicates a possible atmosphere, one has not been detected definitively. Our analysis relies on the Doppler cross-correlation technique, which takes advantage of the high spectral resolution and broad wavelength coverage of our data, to search for the thousands of absorption features from hydrogen-, carbon-, and nitrogen-rich molecular species in the planetary atmosphere. Although we are unable to detect an atmosphere around 55 Cancri e, we do place strong constraints on the levels of HCN, NH3, and C2H2 that may be present. In particular, at a mean molecular weight of 5 amu, we can rule out the presence of HCN in the atmosphere down to a volume mixing ratio (VMR) of 0.02%, NH3 down to a VMR of 0.08%, and C2H2 down to a VMR of 1.0%. If the mean molecular weight is relaxed to 2 amu, we can rule out the presence of HCN, NH3, and C2H2 down to VMRs of 0.001%, 0.0025%, and 0.08%, respectively. Our results reduce the parameter space of possible atmospheres consistent with the analysis of Hubble Space Telescope/WFC3 observations by Tsiaras et al. and indicate that if 55 Cancri e harbors an atmosphere, it must have a high mean molecular weight or clouds.

An IRTF-iSHELL Survey of 4.52–5.25 μm CO Spectra in Protoplanetary Disks of Intermediate-mass Stars: Preliminary Sample and Analysis

Abstract We are conducting a survey of high-resolution near-infrared CO rovibrational spectra in protoplanetary disks around young intermediate-mass stars. We use IRTF-iSHELL with the 0.″375 and 0.″75 slits, providing 4 km s−1 and 6 km s−1 resolution and covering 4.52–5.25 μm in one single exposure. This includes part of the rovibrational R branch and most of the P branch of the CO fundamental band (Δv = 1), one of the best tracers of warm/hot gas in disks. The high quality of the spectra and the large sample covered in this survey will support multiple investigations to study the structure, kinematics, composition, and evolution of the inner 10 au in disks for years to come. The survey currently includes ∼30 stars mostly within 200 pc, complementing extensive imaging campaigns that are observing their disks at optical, infrared, and millimeter wavelengths and revealing structures and planets.

First Detection of Hydroxyl Radical Emission from an Exoplanet Atmosphere: High-dispersion Characterization of WASP-33b Using Subaru/IRD

Abstract We report the first detection of a hydroxyl radical (OH) emission signature in the planetary atmosphere outside the solar system, in this case, in the dayside of WASP-33b. We analyze high-resolution near-infrared emission spectra of WASP-33b taken using the InfraRed Doppler spectrograph on the 8.2 m Subaru telescope. The telluric and stellar lines are removed using a detrending algorithm, SysRem. The residuals are then cross-correlated with OH and H2O planetary spectrum templates produced using several different line lists. We check and confirm the accuracy of OH line lists by cross-correlating with the spectrum of GJ 436. As a result, we detect the emission signature of OH at K p of km s−1 and v sys of −0.3 km s−1 with a signal-to-noise ratio (S/N) of 5.4 and a significance of 5.5σ. Additionally, we marginally detect H2O emission in the H-band with an S/N of 4.0 and a significance of 5.2σ using the POKAZATEL line list. However, no significant signal is detected using the HITEMP 2010, which might be due to differences in line positions and strengths, as well as the incompleteness of the line lists. Nonetheless, this marginal detection is consistent with the prediction that H2O is mostly thermally dissociated in the upper atmosphere of the ultra-hot Jupiters. Therefore, along with CO, OH is expected to be one of the most abundant O-bearing molecules in the dayside atmosphere of ultra-hot Jupiters and should be considered when studying their atmospheres.

As the Worlds Turn: Constraining Spin Evolution in the Planetary-mass Regime

Abstract To understand how planetary spin evolves and traces planet formation processes, we measure rotational line broadening in eight planetary-mass objects (PMOs) of various ages (1–800 Myr) using near-infrared high-resolution spectra from NIRSPEC/Keck. Combining these with published rotation rates, we compile 27 PMO spin velocities, 16 of which derive from our NIRSPEC/Keck program. Our data are consistent with spin velocities v scaling with planetary radius R as v ∝ 1/R. We conclude that spin angular momentum is conserved as objects cool and contract over the sampled age range. The PMOs in our sample spin at rates that are approximately an order of magnitude below their break-up values, consistent with the hypothesis that they were spun down by magnetized circum-PMO disks (CPDs) during the formation era at ages ≲a few Myr. There is a factor of 4–5 variation in spin velocity that has yet to be understood theoretically. It also remains to be seen whether spin evolves on timescales ≳1 Gyr for PMOs, as it does for stars and high-mass brown dwarfs emitting magnetized winds.

Elemental abundances of M dwarfs based on high-resolution near-infrared spectra: Verification by binary systems

ABSTRACT M dwarfs are prominent targets of planet search projects, and their chemical composition is crucial to understanding the formation process or interior of orbiting exoplanets. However, measurements of elemental abundances of M dwarfs have been limited due to difficulties in the analysis of their optical spectra. We conducted a detailed chemical analysis of five M dwarfs (Teff ∼ 3200–3800 K), which form binary systems with G/K-type stars, by performing a line-by-line analysis based on high-resolution (R ∼ 80000) near-infrared (960–1710 nm) spectra obtained with CARMENES (Calar Alto high-Resolution search for M dwarfs with Exo-earths with Near-infrared and optical Échelle Spectrographs). We determined the chemical abundances of eight elements (Na, Mg, K, Ca, Ti, Cr, Mn, and Fe), which are in agreement with those of the primary stars within measurement errors (∼0.2 dex). Through the analysis process, we investigated the unique behavior of atomic lines in a cool atmosphere. Most atomic lines are sensitive to changes in the abundance of not only the corresponding elements but also other elements, especially dominant electron donors such as Na and Ca. The Ti i lines show a negative correlation with the overall metallicity at Teff < 3400 K due to the consumption of neutral titanium by the formation of TiO molecules. These findings indicate that to estimate the overall metallicity or the abundance of any element correctly, we need to determine the abundances of other individual elements consistently.

Obliquity Constraints on an Extrasolar Planetary-mass Companion

Abstract We place the first constraints on the obliquity of a planetary-mass companion outside of the solar system. Our target is the directly imaged system 2MASS J01225093–2439505 (2M0122), which consists of a 120 Myr 0.4 M ⊙ star hosting a 12–27 M J companion at 50 au. We constrain all three of the system’s angular-momentum vectors: how the companion spin axis, the stellar spin axis, and the orbit normal are inclined relative to our line of sight. To accomplish this, we measure projected rotation rates (v sin i) for both the star and the companion using new near-infrared high-resolution spectra with NIRSPEC at Keck Observatory. We combine these with a new stellar photometric rotation period from TESS and a published companion rotation period from Hubble Space Telescope to obtain spin-axis inclinations for both objects. We also fitted multiple epochs of astrometry, including a new observation with NIRC2/Keck, to measure 2M0122b’s orbital inclination. The three line-of-sight inclinations place limits on the true de-projected companion obliquity and stellar obliquity. We find that while the stellar obliquity marginally prefers alignment, the companion obliquity tentatively favors misalignment. We evaluate possible origin scenarios. While collisions, secular spin–orbit resonances, and Kozai–Lidov oscillations are unlikely, formation by gravitational instability in a gravito-turbulent disk—the scenario favored for brown dwarf companions to stars—appears promising.