Abstract
We derive distances and masses of stars from the Sloan Digital Sky Survey (SDSS) Apache Point Observatory Galactic Evolution Experiment Data Release 17 using simple neural networks. Training ...data for distances comes from Gaia EDR3, supplemented by literature distances for star clusters. For masses, the network is trained using asteroseismic masses for evolved stars and isochrone masses for main-sequence stars. The models are trained on effective temperature, surface gravity, metallicity, and carbon and nitrogen abundances. We found that our distance predictions have median fractional errors that range from ≈20% at low log
g
and ≈10% at higher log
g
with a standard deviation of ≈11%. The mass predictions have a standard deviation of ±12%. Using the masses, we derive ages for evolved stars based on the correspondence between mass and age for giant stars given by isochrones. The results are compiled into a Value Added Catalog called DistMass that contains distances and masses for 733,901 independent spectra, plus ages for 396,548 evolved stars.
Abstract Data-driven models, which apply machine learning to infer physical properties from large quantities of data, have become increasingly important for extracting stellar properties from ...spectra. In general, these methods have been applied to data in one wavelength regime or another. For example, APOGEE Net has been applied to near-IR spectra from the Sloan Digital Sky Survey (SDSS)–V APOGEE survey to predict stellar parameters ( T eff , log g , and Fe/H) for all stars with T eff from 3000 to 50,000 K, including pre-main-sequence stars, OB stars, main-sequence dwarfs, and red giants. The increasing number of large surveys across multiple wavelength regimes provides the opportunity to improve data-driven models through learning from multiple data sets at once. In SDSS-V, a number of spectra of stars will be observed not just with APOGEE in the near-IR, but also with BOSS in the optical regime. Here, we aim to develop a complementary model, BOSS Net, that will replicate the performance of APOGEE Net in these optical data through label transfer. We further improve the model by extending it to brown dwarfs, as well as white dwarfs, resulting in a comprehensive coverage between 1700 < T eff < 100,000 K and 0 < log g < 10, to ensure BOSS Net can reliably measure parameters of most of the commonly observed objects within this parameter space. We also update APOGEE Net to achieve a comparable performance in the near-IR regime. The resulting models provide a robust tool for measuring stellar evolutionary states, and, in turn, enable characterization of the star-forming history of the Galaxy.
ABSTRACT
Interacting binary stars undergo evolution that is significantly different from single stars, thus, a larger sample of such systems with precisely determined stellar parameters is needed to ...understand the complexities of this process. We present an analysis of a hierarchical triple containing a spectroscopically double-lined eclipsing binary, 2M16+21. Our calculations show that this system has undergone significant mass transfer, with the current mass and radius of the donor of 0.33 M⊙ and 2.55 R⊙, as well as the accretor of 1.37 M⊙ and 2.20 R⊙, resulting in a mass ratio of 4.2. Despite the already significant mass loss from the donor, shedding well over half its initial gas, mass transfer remains active. The shock from the accretion has produced a spot on the surface of the accretor that is ∼2 times hotter than the photosphere, reaching temperatures of ∼10 000 K and producing significant UV excess. This shock temperature is comparable to what is seen in the pre-main sequence stars that undergo active accretion. The compactness of the hot spot of just ∼2° is one of the smallest observed in systems exhibiting binary mass transfer, pointing to the recency of its formation, as such it can be used to explicitly trace the point of impact of the accretion stream. The donor of this system may be a sub-sub-giant; comparing it with systems with similar initial conditions may help with understanding the formation processes of such stars.
Abstract
We present a large-scale study of stellar rotation for T Tauri stars in the Orion star-forming complex. We use the projected rotational velocity (
v
sin
(
i
)
) estimations reported by the ...APOGEE-2 collaboration as well as individual masses and ages derived from the position of the stars in the HR diagram, considering Gaia-EDR3 parallaxes and photometry plus diverse evolutionary models. We find an empirical trend for
v
sin
(
i
)
decreasing with age for low-mass stars (0.4
M
⊙
<
M
*
< 1.2
M
⊙
). Our results support the existence of a mechanism linking
v
sin
(
i
)
to the presence of accreting protoplanetary disks, responsible for regulating stellar rotation on timescales of about 6 Myr, which is the timescale in which most of the T Tauri stars lose their inner disk. Our results provide important constraints to models of rotation in the early phases of evolution of young stars and their disks.
Abstract
The rotation rates of main-sequence stars slow over time as they gradually lose angular momentum to their magnetized stellar winds. The rate of angular momentum loss depends on the strength ...and morphology of the magnetic field, the mass-loss rate, and the stellar rotation period, mass, and radius. Previous observations suggested a shift in magnetic morphology between two F-type stars with similar rotation rates but very different ages (88 Leo and
ρ
CrB). In this Letter, we identify a comparable transition in an evolutionary sequence of solar analogs with ages between 2–7 Gyr. We present new spectropolarimetry of 18 Sco and 16 Cyg A and B from the Large Binocular Telescope, and we reanalyze previously published Zeeman Doppler images of HD 76151 and 18 Sco, providing additional constraints on the nature and timing of this transition. We combine archival X-ray observations with updated distances from Gaia to estimate mass-loss rates, and we adopt precise stellar properties from asteroseismology and other sources. We then calculate the wind braking torque for each star in the evolutionary sequence, demonstrating that the rate of angular momentum loss drops by more than an order of magnitude between the ages of HD 76151 and 18 Sco (2.6–3.7 Gyr) and continues to decrease modestly to the age of 16 Cyg A and B (7 Gyr). We suggest that this magnetic transition may represent a disruption of the global dynamo arising from weaker differential rotation, and we outline plans to probe this phenomenon in additional stars spanning a wide range of spectral types.
We present the first APOKASC catalog of spectroscopic and asteroseismic data for dwarfs and subgiants. Asteroseismic data for our sample of 415 objects have been obtained by the Kepler mission in ...short (58.5 s) cadence, and light curves span from 30 up to more than 1000 days. The spectroscopic parameters are based on spectra taken as part of the Apache Point Observatory Galactic Evolution Experiment and correspond to Data Release 13 of the Sloan Digital Sky Survey. We analyze our data using two independent scales, the spectroscopic values from DR13 and those derived from SDSS griz photometry. We use the differences in our results arising from these choices as a test of systematic temperature uncertainties and find that they can lead to significant differences in the derived stellar properties. Determinations of surface gravity ( ), mean density ( ), radius (R), mass (M), and age (τ) for the whole sample have been carried out by means of (stellar) grid-based modeling. We have thoroughly assessed random and systematic error sources in the spectroscopic and asteroseismic data, as well as in the grid-based modeling determination of the stellar quantities provided in the catalog. We provide stellar properties determined for each of the two scales. The median combined (random and systematic) uncertainties are 2% (0.01 dex; ), 3.4% ( ), 2.6% (R), 5.1% (M), and 19% (τ) for the photometric scale and 2% ( ), 3.5% ( ), 2.7% (R), 6.3% (M), and 23% (τ) for the spectroscopic scale. We present comparisons with stellar quantities in the asteroseismic catalog by Chaplin et al. that highlight the importance of having metallicity measurements for determining stellar parameters accurately. Finally, we compare our results with those coming from a variety of sources, including stellar radii determined from TGAS parallaxes and asteroseismic analyses based on individual frequencies. We find a very good agreement for all inferred quantities. The latter comparison, in particular, gives strong support to the determination of stellar quantities based on global seismology, a relevant result for future missions such as TESS and PLATO.
Searching for young runaways across the sky Kounkel, Marina; Mcbride, Aidan; Stassun, Keivan G ...
Monthly notices of the Royal Astronomical Society,
10/2022, Volume:
517, Issue:
2
Journal Article
Peer reviewed
ABSTRACT
We present a catalogue of 3354 candidate young stars within 500 pc that appear to have been ejected from their parent associations with relative speeds of >5 km s−1. These candidates have ...been homogeneously selected through performing a 2D spherical traceback of previously identified pre-main-sequence candidates to various star-forming regions, ensuring that the traceback age as well as the estimated age of a star is consistent with the age of the population, and excluding contaminants from the nearby moving groups that follow the dominant velocity currents in the field. Among the identified candidates we identify a number of pairs that appear to have interacted in the process of the ejection; these pairs have similar traceback time, and their trajectory appears to be diametrically opposite from each other, or they have formed a wide binary in the process. As the selection of these candidates is performed solely in 2D, spectral follow-up is necessary for their eventual confirmation. Unfortunately, recently released Gaia DR3 radial velocities appear to be unsuitable for characterizing the kinematics of low-mass stars with ages <100 Myr, as the accretion, activity, and a variety of other spectral features that make them distinct from the more evolved stars do not appear to have been accurately accounted for in the data, resulting in significant artificially inflated scatter in their RV distribution.
Abstract
We present higher-order multiplicity results for 60 solar-type spectroscopic binaries based on 0.75
μ
m imaging data taken by the robotic adaptive optics (Robo-AO) system at the Kitt Peak ...2.1 m telescope. Our contrast curves show sensitivity up to ∼5 mag at ∼1″ separation; at very small separations, we identify candidate companions from image deviations relative to the point spread function. We find candidate tertiary companions for 62% of our binaries overall, but we find that this fraction is a strong function of the inner binary orbital period; it ranges from ∼47% for
P
bin
> 30 days to as high as ∼90% for
P
bin
≲ 5 days. We similarly find an increasing tertiary companion frequency for shorter-period binaries in a secondary sample of Kepler eclipsing binaries observed by Robo-AO. Using Gaia distances, we estimate an upper limit orbital period for each tertiary candidate and compare the tertiary-to-binary period ratios for systems in the field versus those in star-forming regions. Taken all together, these results provide further evidence for angular momentum transfer from three-body interactions, resulting in tight binaries with tertiaries that widen from pre-main-sequence to field ages.
We present bolometric fluxes and angular diameters for over 1.6 million stars in the Tycho-2 catalog, determined using previously determined empirical color-temperature and color-flux relations. We ...vet these relations via full fits to the full broadband spectral energy distributions for a subset of benchmark stars and perform quality checks against the large set of stars for which spectroscopically determined parameters are available from LAMOST, RAVE, and/or APOGEE. We then estimate radii for the 355,502 Tycho-2 stars in our sample whose Gaia DR1 parallaxes are precise to . For these stars, we achieve effective temperature, bolometric flux, and angular diameter uncertainties of the order of 1%-2% and radius uncertainties of order 8%, and we explore the effect that imposing spectroscopic effective temperature priors has on these uncertainties. These stellar parameters are shown to be reliable for stars with 7000 K. The over half a million bolometric fluxes and angular diameters presented here will serve as an immediate trove of empirical stellar radii with the Gaia second data release, at which point effective temperature uncertainties will dominate the radius uncertainties. Already, dwarf, subgiant, and giant populations are readily identifiable in our purely empirical luminosity-effective temperature (theoretical) Hertzsprung-Russell diagrams.
Phase curve observations provide an opportunity to study the energy budgets of exoplanets by quantifying the amount of heat redistributed from their daysides to their nightsides. Theories of phase ...curves for hot Jupiters have focused on the balance between radiation and dynamics as the primary parameter controlling heat redistribution. However, recent phase curves have shown deviations from the trends that emerge from this theory, which has led to work on additional processes that may affect hot Jupiter energy budgets. One such process, molecular hydrogen dissociation and recombination, can enhance energy redistribution on ultra-hot Jupiters with temperatures above ∼2000 K. In order to study the impact of H2 dissociation on ultra-hot Jupiters, we present a phase curve of KELT-9b observed with the Spitzer Space Telescope at 4.5 m. KELT-9b is the hottest known transiting planet, with a 4.5 m dayside brightness temperature of and a nightside temperature of . We observe a phase curve amplitude of 0.609 0.020 and an offset of . The observed amplitude is too small to be explained by a simple balance between radiation and advection. General circulation models (GCMs) and an energy balance model that include the effects of H2 dissociation and recombination provide a better match to the data. The GCMs, however, predict a maximum phase offset of 5°, which disagrees with our observations at >5 confidence. This discrepancy may be due to magnetic effects in the planet's highly ionized atmosphere.
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