arXiv subjects
Publications and source records attributed to Adam Burgasser.
We present low resolution infrared spectral standards in the 0.76 to 5.0 {\mu}m range based on JWST NIRspec Prism data from deep sky surveys. Our standards encompass spectral types M, L, and T and dwarf and subdwarf metallicity classes. The standards extend ground based spectral templates and enable classification of low temperature stellar substellar discoveries from deep JWST NIRSpec data.
We present the discovery and validation of a super-Earth planet orbiting the M dwarf star TOI-1846 (TIC 198385543). The host star(Kmag = 9.6)is located 47 pc away and has a radius of Rs=0.41+/-0.01R_Sun,a mass of Ms=0.40+/-0.02M_Sun and an effective temperature of Teff=3568+/-44K. Our analyses are based on joint modelling of TESS photometry and ground-based multi-color photometric data. We also use high-resolution imaging and archival images, as well as statistical validation techniques to support the planetary system nature. We find that TOI-1846b is a super-Earth sized planet with radius of Rp=1.79+/-0.07R_Earth and a predicted mass of Mp=4.4+1.6-1.0M_Earth (from the Chen & Kipping relation) on a 3.9 d orbit, with an equilibrium temperature of Teq=589+/-20K (assuming a null Bond Albedo) and an incident flux of Sp=17.6+/-2.0S_Earth. Based on the two RV measurements obtained with the TRES spectrograph and high-resolution imaging, a non-planetary transiting companion is excluded. With a radius of ~1.8R_Earth, TOI-1846b is within the sparsely populated radius range around 2R_Earth known as the radius gap (or radius valley). This discovery can contribute to refining the precise location of the radius valley for small planets orbiting bright M dwarfs, thereby enhancing our understanding of planetary formation and evolution processes.
Near-infrared spectra from the IRTF/SpeX and Blanco/ARCoIRIS telescope/instrument combinations are used for spectroscopic classification, to measure radial velocities and for the inference of astrophysical properties of 51 Gaia-selected nearby ultracool dwarfs. In this sample, 44 are newly classified in the near infrared. All but one of the UCDs are within 100 pc, and 37 lie within 50 pc. We find a total of 26 M-types, 24 L-types and one T-type in our sample. The positions of the majority of the UCDs on colour-magnitude diagrams and with evolutionary cooling track plots indicate that they are largely old and stellar in nature. There are a few UCDs of particular interest which lie away from expected trends, highlighting potential young, binary and thick disc/subdwarf UCDs. From spectral and kinematic analyses, we identify UCDs of particular interest for further investigation, including seven potentially young UCDs, three thick disc UCDs, one subdwarf, six wide binaries, and six unresolved binaries.
We present the discovery of 118 new ultracool dwarf candidates, discovered using a new machine learning tool, named \texttt{SMDET}, applied to time series images from the Wide-field Infrared Survey Explorer. We gathered photometric and astrometric data to estimate each candidate's spectral type, distance, and tangential velocity. This sample has a photometrically estimated spectral class distribution of 28 M dwarfs, 64 L dwarfs, and 18 T dwarfs. We also identify a T subdwarf candidate, two extreme T subdwarf candidates, and two candidate young ultracool dwarfs. Five objects did not have enough photometric data for any estimations to be made. To validate our estimated spectral types, spectra were collected for 2 objects, yielding confirmed spectral types of T5 (estimated T5) and T3 (estimated T4). Demonstrating the effectiveness of machine learning tools as a new large-scale discovery technique.
The ESA space mission Euclid was launched on July 1st, 2023 and is undergoing its science verification phase. In this invited review we show that Euclid means a before and an after for our understanding of ultra-cool dwarfs and substellar-mass objects and their connections with stars, exoplanets and the Milky Way. Euclid enables the study with unprecedented statistical significance a very large ensemble of ultracool dwarfs, the identification of new types of substellar objects, and the determination of the substellar binary fraction and the Initial Mass Function (IMF) in diverse galactic environments from the nearest stellar nurseries to the ancient relics of Galactic formation.
HISPEC is a new, high-resolution near-infrared spectrograph being designed for the W.M. Keck II telescope. By offering single-shot, R=100,000 between 0.98 - 2.5 um, HISPEC will enable spectroscopy of transiting and non-transiting exoplanets in close orbits, direct high-contrast detection and spectroscopy of spatially separated substellar companions, and exoplanet dynamical mass and orbit measurements using precision radial velocity monitoring calibrated with a suite of state-of-the-art absolute and relative wavelength references. MODHIS is the counterpart to HISPEC for the Thirty Meter Telescope and is being developed in parallel with similar scientific goals. In this proceeding, we provide a brief overview of the current design of both instruments, and the requirements for the two spectrographs as guided by the scientific goals for each. We then outline the current science case for HISPEC and MODHIS, with focuses on the science enabled for exoplanet discovery and characterization. We also provide updated sensitivity curves for both instruments, in terms of both signal-to-noise ratio and predicted radial velocity precision.
How many low-mass stars, brown dwarfs and free-floating planets are in the Milky Way? And how are they distributed in our Galaxy? Recent studies of Milky Way interlopers in high-redshift observations have revealed a 150-300 pc thick disk of these cool stars with 7% of the M-dwarfs in an oblate stellar halo. One can use the High Latitude Survey with the Roman Space Telescope to search for Galactic ultracool dwarfs (spectral classes M, L, T, and Y) to accurately model the 3D structure and the temperature and chemical evolution of the Milky Way disk in these low-mass (sub)stellar objects. Accurate typing has been shown to work on HST grism and photometric data using machine learning techniques. Such an approach can also be applied to Roman photometry, producing accurate photometric typing to within two subtypes. The High Latitude Survey provides enough statistical power to model the Milky Way structural components (thin and thick disks and halo) for M-, L- and T/Y-dwarfs. This approach has the benefit to allow us to constrain scale-lengths, scale-heights and densities, as well as the relative position of our Sun with respect to the disk of dwarf stars of our Milky Way. The total number of each brown dwarf type can be used to infer both the low-mass end of the Galaxy-wide Initial Mass Function (IMF) for the first time, the formation history of low-mass stellar and substellar objects, and the fraction of low-mass stars in the halo, a statistic that can test cold dark matter structure formation theories.
We have been exploring large spectroscopic databases such as SDSS to search for unique stars with extremely low iron content with the goal of extracting detailed information from the early phases of the Galaxy. We recently identified two extremely iron-poor dwarf stars J0815+4729 (Aguado et al. 2018a) and J0023+0307 (Aguado et al. 2018b) from SDSS/BOSS database and confirmed from high-quality spectra taken with ISIS and OSIRIS spectrographs at the 4.2m WHT and 10.4m GTC telescopes, respectively, located in La Palma (Canary Islands, Spain). We have also acquired high-resolution spectroscopy with UVES at 8.2m VLT telescope (Paranal, ESO, Chile) and HIRES at the 10m KeckI telescope (Mauna Kea, Hawaii, USA), uncovering the unique abundance pattern of these stars, that reveal e.g. the extreme CNO abundances in J0815+4729 with ratios [X/Fe]~$> 4$ (Gonz\'alez Hern\'andez et al. 2020). In addition, we are able to detect Li at the level of the lithium plateau in J0023+0307 (Aguado et al. 2019a), whereas we are only able to give a Li upper-limit 0.7 dex below the lithium plateau in J0815+4729, thus adding more complexity to the cosmological lithium problem. New upcoming surveys such as WEAVE, 4MOST and DESI will likely allow us to discover new interesting extremely iron-poor stars, that will certainly contribute to our understanding of the Early Galaxy, and the properties of the first stars and the first supernovae.
This paper documents the seventeenth data release (DR17) from the Sloan Digital Sky Surveys; the fifth and final release from the fourth phase (SDSS-IV). DR17 contains the complete release of the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey, which reached its goal of surveying over 10,000 nearby galaxies. The complete release of the MaNGA Stellar Library (MaStar) accompanies this data, providing observations of almost 30,000 stars through the MaNGA instrument during bright time. DR17 also contains the complete release of the Apache Point Observatory Galactic Evolution Experiment 2 (APOGEE-2) survey which publicly releases infra-red spectra of over 650,000 stars. The main sample from the Extended Baryon Oscillation Spectroscopic Survey (eBOSS), as well as the sub-survey Time Domain Spectroscopic Survey (TDSS) data were fully released in DR16. New single-fiber optical spectroscopy released in DR17 is from the SPectroscipic IDentification of ERosita Survey (SPIDERS) sub-survey and the eBOSS-RM program. Along with the primary data sets, DR17 includes 25 new or updated Value Added Catalogs (VACs). This paper concludes the release of SDSS-IV survey data. SDSS continues into its fifth phase with observations already underway for the Milky Way Mapper (MWM), Local Volume Mapper (LVM) and Black Hole Mapper (BHM) surveys.
We present the discovery of rapid photometric variability in three ultra-cool dwarfs from long-duration monitoring with the Spitzer Space Telescope. The T7, L3.5, and L8 dwarfs have the shortest photometric periods known to date: ${1.080}^{+0.004}_{-0.005}$ h, ${1.14}^{+0.03}_{-0.01}$ h, and ${1.23}^{+0.01}_{-0.01}$ h, respectively. We confirm the rapid rotation through moderate-resolution infrared spectroscopy, which reveals projected rotational velocities between 79 and 104 km s$^{-1}$. We compare the near-infrared spectra to photospheric models to determine the objects' fundamental parameters and radial velocities. We find that the equatorial rotational velocities for all three objects are $\gtrsim$100 km s$^{-1}$. The three L and T dwarfs reported here are the most rapidly spinning and likely the most oblate field ultra-cool dwarfs known to date. Correspondingly, all three are excellent candidates for seeking auroral radio emission and net optical/infrared polarization. As of this writing, 78 L-, T-, and Y-dwarf rotation periods have now been measured. The clustering of the shortest rotation periods near 1 h suggests that brown dwarfs are unlikely to spin much faster.
Variations in the reflective properties of the bulk material that comprises the surface of land-dominated planets will affect the planetary energy balance by interacting differently with incident radiation from the host star. Furthermore, low-mass cool stars, such as nearby M8V dwarf TRAPPIST-1, emit a significant fraction of their flux in longer wavelengths relative to the Sun in regions where terrestrial materials may exhibit additional variability in albedo. Using the Community Earth System Model (CESM) we investigate the effect of the composition of the land surface and its albedo on planetary climate in the context of spatially homogeneous, entirely land-covered planets with dry atmospheres at the orbital separation of TRAPPIST-1d, TRAPPIST-1e, and TRAPPIST-1f. We use empirically derived spectra of four terrestrial compositional endmembers (granite, calcite, aridisol, and dune sand) and a composite spectrum of TRAPPIST-1 for these simulations and compare these model output to an aquaplanet and several Sol-spectrum control cases. We report a difference of approximately 50 K in global mean surface temperature, variations in atmospheric rotational features, and a reduction in cross-equatorial heat transport between scenarios in which materials with higher albedo in the infrared (calcite and dune sand) were used and those with more absorptive crustal material, such as granite or dry soils. An aquaplanet TRAPPIST-1d scenario results in an unstable runaway greenhouse regime. Therefore, we demonstrate that determining the composition and albedo of continental landmasses is crucial for making accurate determinations of the climate of terrestrial exoplanets.
We have collected transit times for the TRAPPIST-1 system with the Spitzer Space Telescope over four years. We add to these ground-based, HST and K2 transit time measurements, and revisit an N-body dynamical analysis of the seven-planet system using our complete set of times from which we refine the mass ratios of the planets to the star. We next carry out a photodynamical analysis of the Spitzer light curves to derive the density of the host star and the planet densities. We find that all seven planets' densities may be described with a single rocky mass-radius relation which is depleted in iron relative to Earth, with Fe 21 wt% versus 32 wt% for Earth, and otherwise Earth-like in composition. Alternatively, the planets may have an Earth-like composition, but enhanced in light elements, such as a surface water layer or a core-free structure with oxidized iron in the mantle. We measure planet masses to a precision of 3-5%, equivalent to a radial-velocity (RV) precision of 2.5 cm/sec, or two orders of magnitude more precise than current RV capabilities. We find the eccentricities of the planets are very small; the orbits are extremely coplanar; and the system is stable on 10 Myr timescales. We find evidence of infrequent timing outliers which we cannot explain with an eighth planet; we instead account for the outliers using a robust likelihood function. We forecast JWST timing observations, and speculate on possible implications of the planet densities for the formation, migration and evolution of the planet system.
MAAT is proposed as a visitor mirror-slicer optical system that will allow the OSIRIS spectrograph on the 10.4-m Gran telescopio CANARIAS (GTC) the capability to perform Integral Field Spectroscopy (IFS) over a seeing-limited FoV 14.20''x10'' with a slice width of 0.303''. MAAT@GTC will enhance the resolution power of OSIRIS by 1.6 times as compared to its 0.6'' wide long-slit. All the eleven OSIRIS grisms and volume-phase holographic gratings will be available to provide broad spectral coverage with moderate resolution (R=600 up to 4100) in the 3600 - 10000 {\AA} wavelength range. MAAT unique observing capabilities will broaden its use to the needs of the GTC community to unveil the nature of most striking phenomena in the universe well beyond time-domain astronomy. The GTC equipped with OSIRIS+MAAT will also play a fundamental role in synergy with other facilities, some of them operating on the northern ORM at La Palma. This White Paper presents the different aspects of MAAT@GTC - including scientific and technical specifications, outstanding science cases, and an outline of the instrument concept.
We present spectroscopic determinations of the effective temperatures, surface gravities and metallicities for 21 M-dwarfs observed at high-resolution (R $\sim$ 22,500) in the \textit{H}-band as part of the SDSS-IV APOGEE survey. The atmospheric parameters and metallicities are derived from spectral syntheses with 1-D LTE plane parallel MARCS models and the APOGEE atomic/molecular line list, together with up-to-date H$_{2}$O and FeH molecular line lists. Our sample range in $T_{\rm eff}$ from $\sim$ 3200 to 3800K, where eleven stars are in binary systems with a warmer (FGK) primary, while the other 10 M-dwarfs have interferometric radii in the literature. We define an $M_{K_{S}}$--Radius calibration based on our M-dwarf radii derived from the detailed analysis of APOGEE spectra and Gaia DR2 distances, as well as a mass-radius relation using the spectroscopically-derived surface gravities. A comparison of the derived radii with interferometric values from the literature finds that the spectroscopic radii are slightly offset towards smaller values, with $\Delta$ = -0.01 $\pm$ 0.02 $R{\star}$/$R_{\odot}$. In addition, the derived M-dwarf masses based upon the radii and surface gravities tend to be slightly smaller (by $\sim$5-10\%) than masses derived for M-dwarf members of eclipsing binary systems for a given stellar radius. The metallicities derived for the 11 M-dwarfs in binary systems, compared to metallicities obtained for their hotter FGK main-sequence primary stars from the literature, shows excellent agreement, with a mean difference of [Fe/H](M-dwarf - FGK primary) = +0.04 $\pm$ 0.18 dex, confirming the APOGEE metallicity scale derived here for M-dwarfs.
M dwarfs have enormous potential for our understanding of structure and formation on both Galactic and exoplanetary scales through their properties and compositions. However, current atmosphere models have limited ability to reproduce spectral features in stars at the coolest temperatures ($T_{\rm eff} < 4200\,$K) and to fully exploit the information content of current and upcoming large-scale spectroscopic surveys. Here we present a catalog of spectroscopic temperatures, metallicities, and spectral types for 5875 M dwarfs in the Apache Point Observatory Galactic Evolution Experiment (APOGEE) and Gaia DR2 surveys using The Cannon: a flexible, data-driven spectral-modeling and parameter-inference framework demonstrated to estimate stellar-parameter labels ($T_{\rm eff}$, log$g$, [Fe/H], and detailed abundances) to high precision. Using a training sample of 87 M dwarfs with optically derived labels spanning $2860 < T_{\rm eff} < 4130\,$K calibrated with bolometric temperatures, and $-0.5 < $[Fe/H]$ < 0.5\,$dex calibrated with FGK binary metallicities, we train a two-parameter model with predictive accuracy (in cross-validation) to $77\,$K and $0.09\,$dex respectively. We also train a one-dimensional spectral classification model using 51 M dwarfs with Sloan Digital Sky Survey optical spectral types ranging from M0 to M6, to predictive accuracy of 0.7 types. We find Cannon temperatures to be in agreement to within $60\,$K compared to a subsample of 1702 sources with color-derived temperatures, and Cannon metallicities to be in agreement to within $0.08\,$dex metallicity compared to a subsample of 15 FGK+M or M+M binaries. Finally, our comparison between Cannon and APOGEE pipeline (ASPCAP DR14) labels finds that ASPCAP is systematically biased toward reporting higher temperatures and lower metallicities for M dwarfs.
This paper documents the sixteenth data release (DR16) from the Sloan Digital Sky Surveys; the fourth and penultimate from the fourth phase (SDSS-IV). This is the first release of data from the southern hemisphere survey of the Apache Point Observatory Galactic Evolution Experiment 2 (APOGEE-2); new data from APOGEE-2 North are also included. DR16 is also notable as the final data release for the main cosmological program of the Extended Baryon Oscillation Spectroscopic Survey (eBOSS), and all raw and reduced spectra from that project are released here. DR16 also includes all the data from the Time Domain Spectroscopic Survey (TDSS) and new data from the SPectroscopic IDentification of ERosita Survey (SPIDERS) programs, both of which were co-observed on eBOSS plates. DR16 has no new data from the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey (or the MaNGA Stellar Library "MaStar"). We also preview future SDSS-V operations (due to start in 2020), and summarize plans for the final SDSS-IV data release (DR17).
This white paper proposes leveraging high-quality Gaia data available to the worldwide scientific community and complement it with support from Canadian-related facilities to place Canada as a leader in the fields of stellar associations and exoplanet science, and to train Canadian highly qualified personnel through graduate and post-graduate research grants. Gaia has sparked a new era in the study of stellar kinematics by measuring precise distances and proper motions for 1.3 billion stars. These data have already generated more than 1700 scientific papers and are guaranteed to remain the source of many more papers for the upcoming decades. More than 900 new age-calibrated young low-mass stars have already been discovered as a direct consequence of the second Gaia data release. Some of these may already be host stars to known exoplanet systems or may become so with the progress of the TESS mission that is expected to discover 10,000 nearby transiting exoplanets in the upcoming decade. This places Canada in a strategic position to leverage Gaia data because it has access to several high-resolution spectrometers on 1-4 m class telescopes (e.g. The ESPaDOnS, SPIRou and NIRPS), that would allow to quickly characterize this large number of low-mass stars and their exoplanet systems. This white paper describes the opportunity in such scientific projects that could place Canada as a leader in the fields of stellar associations and exoplanets.
HISPEC (High-resolution Infrared Spectrograph for Exoplanet Characterization) is a proposed diffraction-limited spectrograph for the W.M. Keck Observatory, and a pathfinder for the MODHIS facility project (Multi-Object Diffraction-limited High-resolution Infrared Spectrograph) on the Thirty Meter Telescope. HISPEC/MODHIS builds on diffraction-limited spectrograph designs which rely on adaptively corrected single-mode fiber feeds. Seeing-limited high-resolution spectrographs, by virtue of the conservation of beam etendue, grow in volume following a D^3 power law (D is the telescope diameter), and are subject to daunting challenges associated with their large size. Diffraction-limited spectrographs fed by single mode fibers are decoupled from the telescope input, and are orders of magnitude more compact and have intrinsically stable line spread functions. Their efficiency is directly proportional to the performance of the adaptive optics (AO) system. AO technologies have matured rapidly over the past two decades and are baselined for future extremely large telescopes. HISPEC/MODHIS will take R>100,000 spectra of a few objects in a 10" field-of-view sampled at the diffraction limit (~10-50 mas), simultaneously from 0.95 to 2.4 microns (y-K). The scientific scope ranges from exoplanet infrared precision radial velocities, spectroscopy of transiting, close-in, and directly imaged exoplanets (atmospheric composition and dynamics, RM effect, spin measurements, Doppler imaging), brown dwarf characterization, stellar physics/chemistry, proto-planetary disk kinematics/composition, Solar system, extragalactic science, and cosmology. HISPEC/MODHIS features a compact, cost-effective design optimized to fully exploit the existing Keck-AO and future TMT-NFIRAOS infrastructures and boost the scientific reach of Keck Observatory and TMT soon after first light.