Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Stellarator”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 451 records · Page 25
All sourcesNASA NTRSDOE OSTI
NASA NTRS2013

'Direct' Gas-Phase Metallicities, Stellar Properties, and Local Environments of Emission-Line Galaxies at Redshifts Below 0.90

Using deep narrow-band (NB) imaging and optical spectroscopy from the Keck telescope and the Multi Mirror Telescope (MMT), we identify a sample of 20 emission-line galaxies (ELGs) at z = 0.065-0.90 where the weak auroral emission line, [O iii] lambda4363, is detected at >=3sigma. These detections allow us to determine the gas-phase metallicity using the "direct" method. With electron temperature measurements, and dust attenuation corrections from Balmer decrements, we find that 4 of these low-mass galaxies are extremely metal-poor with 12+log(O/H) <= 7.65 or one-tenth solar. Our most metal-deficient galaxy has 12+log(O/H)= 7.24(+0.45 / −0.30) (95% confidence), similar to some of the lowest metallicity galaxies identified in the local universe. We find that our galaxies are all undergoing significant star formation with average specific star formation rate (SFR) of (100 Myra)(exp −1), and that they have high central SFR surface densities (average of 0.5 Solar M / yr/ sq. kpc). In addition, more than two-thirds of our galaxies have between one and four nearby companions within a projected radius of 100 kpc, which we find is an excess among star-forming galaxies at z =0.4 -- 0.85. We also find that the gas-phase metallicities for a given stellar mass and SFR lie systematically lower than the local stellar M-Z-(SFR) relation by approx. = 0.2 dex (2 sigma significance). These results are partly due to selection effects, since galaxies with strong star formation and low metallicity are more likely to yield [O iii] lambda4363 detections. Finally, the observed higher ionization parameter and high electron density suggest that they are lower redshift analogs to typical z approx. > 1 galaxies.

Direct↗
NASA NTRS2014

Stellar Laboratories: 3. New Ba 5, Ba 6, and Ba 7 Oscillator Strengths and the Barium Abundance in the Hot White Dwarfs G191-B2B and RE 0503-289

Context. For the spectral analysis of high-resolution and high-signal-to-noise (S/N) spectra of hot stars, state-of-the-art non-local thermodynamic equilibrium (NLTE) model atmospheres are mandatory. These are strongly dependent on the reliability of the atomic data that is used for their calculation. Aims. Reliable Ba 5-7 oscillator strengths are used to identify Ba lines in the spectra of the DA-type white dwarf G191−B2B and the DO-type white dwarf RE 0503−289 and to determine their photospheric Ba abundances. Methods. We newly calculated Ba v-vii oscillator strengths to consider their radiative and collisional bound-bound transitions in detail in our NLTE stellar-atmosphere models for the analysis of Ba lines exhibited in high-resolution and high-S/N UV observations of G191−B2B and RE 0503−289. Results. For the first time, we identified highly ionized Ba in the spectra of hot white dwarfs. We detected Ba vi and Ba vii lines in the Far Ultraviolet Spectroscopic Explorer (FUSE) spectrum of RE 0503−289. The Ba vi/Ba vii ionization equilibrium is well reproduced with the previously determined effective temperature of 70 000 K and surface gravity of log g=7.5. The Ba abundance is 3.5 +/- 0.5 × 10(exp−4) (mass fraction, about 23 000 times the solar value). In the FUSE spectrum of G191−B2B, we identified the strongest Ba vii line (at 993.41 Å) only, and determined a Ba abundance of 4.0 +/- 0.5 × 10(exp−6) (about 265 times solar). Conclusions. Reliable measurements and calculations of atomic data are a pre-requisite for stellar-atmosphere modeling. Observed Ba vi-vii line profiles in two white dwarfs' (G191−B2B and RE 0503−289) far-ultraviolet spectra were well reproduced with our newly calculated oscillator strengths. This allowed to determine the photospheric Ba abundance of these two stars precisely.

New Ba V↗
NASA NTRS2016

Evolution of Intrinsic Scatter in the SFR-Stellar Mass Correlation at 0.5 less than z Less Than 3

We present estimates of intrinsic scatter in the star formation rate (SFR)--stellar mass (M*) correlation in the redshift range 0.5 less than z less than 3.0 and in the mass range 10(exp 7) less than M* less than 10(exp 11) solar mass. We utilize photometry in the Hubble Ultradeep Field (HUDF12) and Ultraviolet Ultra Deep Field (UVUDF) campaigns and CANDELS/GOODS-S and estimate SFR, M* from broadband spectral energy distributions and the best-available redshifts. The maximum depth of the UDF photometry (F160W 29.9 AB, 5 sigma depth) probes the SFR--M* correlation down to M* approximately 10(exp 7) solar mass, a factor of 10-100 x lower in M* than previous studies, and comparable to dwarf galaxies in the local universe. We find the slope of the SFR-M* relationship to be near unity at all redshifts and the normalization to decrease with cosmic time. We find a moderate increase in intrinsic scatter with cosmic time from 0.2 to 0.4 dex across the epoch of peak cosmic star formation. None of our redshift bins show a statistically significant increase in intrinsic scatter approximately 100 Myr. Our results are consistent with a picture of gradual and self-similar assembly of galaxies across more than three orders of magnitude in stellar mass from as low as 10(exp 7) solar mass.

Kurczynski, Peter↗
NASA NTRS2016

Stellar Laboratories

For the spectral analysis of high-resolution and high signal-to-noise (SN) spectra of hot stars, state-of-the-art non-local thermodynamic equilibrium (NLTE) model atmospheres are mandatory. These are strongly dependent on the reliability of the atomic data that is used for their calculation. Aims: To identify molybdenum lines in the ultraviolet (UV) spectra of the DA-type white dwarf G191B2B and the DO-type white dwarf RE 0503289 and, to determine their photospheric Mo abundances, reliable Mo iv-vii oscillator strengths are used. Methods: We newly calculated Mo iv-vii oscillator strengths to consider their radiative and collisional bound-bound transitions indetail in our NLTE stellar-atmosphere models for the analysis of Mo lines exhibited in high-resolution and high SN UV observations of RE 0503289.Results. We identified 12 Mo v and nine Mo vi lines in the UV spectrum of RE 0503289 and measured a photospheric Mo abundance of 1.2 3.0 104(mass fraction, 22 500 56 400 times the solar abundance). In addition, from the As v and Sn iv resonance lines,we measured mass fractions of arsenic (0.51.3 105, about 300 1200 times solar) and tin (1.33.2 104, about 14 300 35 200 times solar). For G191B2B, upper limits were determined for the abundances of Mo (5.3 107, 100 times solar) and, in addition, for Kr (1.1106, 10 times solar) and Xe (1.7107, 10 times solar). The arsenic abundance was determined (2.35.9 107, about 21 53 times solar). A new, registered German Astrophysical Virtual Observatory (GAVO) service, TOSS, has been constructed to provide weighted oscillator strengths and transition probabilities.Conclusions. Reliable measurements and calculations of atomic data are a prerequisite for stellar-atmosphere modeling. Observed Mo v-vi line profiles in the UV spectrum of the white dwarf RE 0503289 were well reproduced with our newly calculated oscillator strengths. For the first time, this allowed the photospheric Mo abundance in a white dwarf to be determined.

Rauch, T.↗
NASA NTRS2019

The Sub-Neptune Desert and Its Dependence on Stellar Type: Controlled by Lifetime X-Ray Irradiation

Short-period sub-Neptunes with substantial volatile envelopes are among the most common type of known exoplanets. However, recent studies of the Kepler population have suggested a dearth of sub-Neptunes on highly irradiated orbits, where they are vulnerable to atmospheric photoevaporation. Physically, we expect this "photoevaporation desert" to depend on the total lifetime X-ray and extreme ultraviolet flux, the main drivers of atmospheric escape. In this work, we study the demographics of sub-Neptunes as a function of lifetime exposure to high-energy radiation and host-star mass. We find that for a given present-day insolation, planets orbiting a 0.3 solar mass star experience approximately 100 times more X-ray flux over their lifetimes versus a 1.2 solar mass star. Defining the photoevaporation desert as a region consistent with zero occurrence at 2 sigma, the onset of the desert happens for integrated X-ray fluxes greater than 1.43 times 10 (sup 22) to 8.23 times 10 (sup 20) as a function of planetary radii for 1.8 to 4 Earth radius. We also compare the location of the photoevaporation desert for different stellar types. We find much greater variability in the desert onset in the bolometric flux space compared to the integrated X-ray flux space, suggestive of photoevaporation driven by steady-state stellar X-ray emissions as the dominant control on desert location. Finally, we report tentative evidence for the sub-Neptune valley, first seen around Sun-like stars, for M&K dwarfs. The discovery of additional planets around low-mass stars from surveys such as the Transiting Exoplanet Survey Satellite (TESS) mission will enable detailed exploration of these trends.

Planets and Satellites: Gaseous Planets↗
NASA NTRS2019

Modeling a Carrington-Scale Stellar Superflare and Coronal Mass Ejection from K(exp 1) Cet

Observations from the Kepler mission have revealed frequent superflares on young and active solar-like stars. Superflares result from the large-scale restructuring of stellar magnetic fields, and are associated with the eruption of coronal material (a coronal mass ejection, or CME) and energy release that can be orders of magnitude greater than those observed in the largest solar flares. These catastrophic events, if frequent, can significantly impact the potential habitability of terrestrial exoplanets through atmospheric erosion or intense radiation exposure at the surface. We present results from numerical modeling designed to understand how an eruptive superflare from a young solar-type star, κ(exp 1)Cet, could occur and would impact its astrospheric environment. Our data-inspired, three- dimensional magnetohydrodynamic modeling shows that global-scale shear concentrated near the radial-field polarity inversion line can energize the closed-field stellar corona sufficiently to power a global, eruptive superflare that releases approximately the same energy as the extreme 1859 Carrington event from the Sun. We examine proxy measures of synthetic emission during the flare and estimate the observational signatures of our CME-driven shock, both of which could have extreme space-weather impacts on the habitability of any Earth-like exoplanets. We also speculate that the observed 1986 Robinson-Bopp superflare from κ(exp 1)Cet was perhaps as extreme for that star as the Carrington flare was for the Sun.

Lynch, Benjamin J.↗
NASA NTRS2020

OGLE-2018-BLG-1700L: Microlensing Planet in Binary Stellar System

We report a planet in a binary that was discovered from the analysis of the microlensing event OGLE-2018-BLG-1700. We identify the triple nature of the lens from the fact that the anomaly pattern can be decomposed into two parts produced by two binary-lens events, in which one binary pair has a mass ratio of ∼0.01 between the lens components and the other pair has a mass ratio of ∼0.3. We find two sets of degenerate solutions, in which one solution has a projected separation between the primary and its stellar companion less than the angular Einstein radius θ(E) (close solution), while the other solution has a separation greater than θ(E) (wide solution). From the Bayesian analysis with the constraints of the event timescale and angular Einstein radius, we find that the planet has a mass of 4.4(sup +3.0, sub -2.0) M(J) and the stellar binary components have masses of 0.42 (sup +0.29, sub -0.19) M(ʘ) and 0.12 (sup +0.08, sub -0.05) M(ʘ) , respectively, and the distance to the lens is D(L) = 7.6 (sup +1.2, sub -0.9) kpc. The planet is a circumstellar planet according to the wide solution, while it is a circumbinary planet according to the close solution.

Cheongho Han↗
NASA NTRS2020

Confirmation of the Stellar Binary Microlensing Event, Macho 97-BLG-28

The high-magnification microlensing event MACHO-97-BLG-28 was previously determined to be a binary system composed of either two M dwarfs or an M dwarf and a brown dwarf. We present a revised light-curve model using additional data from the Mt. Stromlo 74″telescope, model estimates of stellar limb darkening, and fitting of the blend separately for each telescope and passband. We find a lensing system with a larger mass ratio, q=0.28±0.01, and smaller projected separation, s=0.61±0.01, than those presented in the original study. We revise the estimate of the lens–source relative proper motion to μ(rel)=2.8±0.5 mas/yr, which indicates that 16.07 yr after the event maximum the lens and source should have separated by 46±8 mas. We revise the radius of the source star using more recent reddening maps and angular diameter–color relations to R(*)=(10.3±1.9) R(ʘ). K- and J-band adaptive optics images of the field taken at this epoch using the NIRC2 imager on the Keck telescope show that the source and lens are still blended, consistent with our light-curve model. With no statistically significant excess flux detection we constrain the mass, M(L)=0.24 (+0.28, -0.12) M(ʘ), and distance, D(L)=7.0±1.0 kpc, of the lensing system. This supports the interpretation of this event as a stellar binary in the Galactic bulge. This lens mass gives a companion mass of M= 0.07(+0.08,-0.04) M(ʘ), close to the boundary between being a star and a brown dwarf.

W. Blackman↗
NASA NTRS2020

Tidal Disruptions of Main Sequence Stars - I. Observable Quantities and their Dependence on Stellar and Black Hole Mass

This paper introduces a series of papers presenting a quantitative theory for the tidal disruption of main-sequence stars by supermassive black holes. Using fully general relativistic hydrodynamics simulations and MESA-model initial conditions, we explore the pericenter-dependence of tidal disruption properties for eight stellar masses(MM0.1510)and six black hole masses( MM105 105BH7). We present here the results most relevant to observations. The effects of internal stellar structure and relativity decouple for both the disruption cross section and the characteristic energy width of the debris. Moreover, the full disruption cross section is almost independent of Må for Må/Me3. Independent of Må, relativistic effects increase the critical pericenter distance for full disruption events by up to a factor of∼3 relative to the Newtonian prediction. The probability of a direct capture is also independent of Må; at MBH/Me;5×106 this probability is equal to the probability of a complete disruption. The breadth of the debris energy distribution ΔE can differ from the standard estimate by factors of0.35−2, depending on Må and MBH, implying a corresponding change(∝(ΔE)−3/2)in the characteristic mass-return timescale. We provide analytic forms, suitable for use in both event rate estimates and parameter inference, to describe all these trends. For partial disruptions, we find a nearly universal relation between the star’s angular momentum and the fraction of Må remaining. Within the “empty loss-cone” regime, partial disruptions must precede full disruptions. These partial disruptions can drastically affect the rate and appearance of subsequent total disruptions.

Taeho Ryu↗
NASA NTRS2020

Tidal Disruptions of Main Sequence Stars - II. Simulation Methodology and Stellar Mass Dependence of the Character of Full Tidal Disruptions

This paper introduces a series of papers presenting a quantitative theory for the tidal disruption of main-sequence stars by supermassive black holes. Using fully general relativistic hydrodynamics simulations and MESA-model initial conditions, we explore the pericenter-dependence of tidal disruption properties for eight stellar masses (0.15 < M_/M<10)and six black hole masses( ́10<MM105 105BH7). We present here the results most relevant to observations. The effects of internal stellar structure and relativity decouple for both the disruption cross section and the characteristic energy width of the debris. Moreover, the full disruption cross section is almost independent of Må for Må/Me3. Independent of Må, relativistic effects increase the critical pericenter distance for full disruption events by up to a factor of ∼3 relative to the Newtonian prediction. The probability of a direct capture is also independent of Må; at MBH/Me5×106this probability is equal to the probability of a complete disruption. The breadth of the debris energy distribution ΔE can differ from the standard estimate by factors of 0.35−2, depending on Må and MBH, implying a corresponding change(∝(ΔE)−3/2)in the characteristic mass-return timescale. We provide analytic forms, suitable for use in both event rate estimates and parameter inference, to describe all these trends. For partial disruptions, we find a nearly universal relation between the star’s angular momentum and the fraction of Må remaining. Within the “empty loss-cone” regime, partial disruptions must precede full disruptions. These partial disruptions can drastically affect the rate and appearance of subsequent total disruptions

Taeho Ryu↗
NASA NTRS2019

The CANDELS/SHARDS Multi-Wavelength Catalog in GOODS-N: Photometry, Photometric Redshifts, Stellar Masses, Emission Line Fluxes and Star Formation Rates

We present a WFC3 F160W (H-band) selected catalog in the CANDELS/GOODS-N field containing photometry from the ultraviolet (UV) to the far-infrared (IR), photometric redshifts and stellar pa-rameters derived from the analysis of the multi-wavelength data. The catalog contains 35,445 sourcesover the 171 arcmin2of the CANDELS F160W mosaic. The 5σdetection limits (within an aperture ofradius 0.′′17) of the mosaic range betweenH= 27.8, 28.2 and 28.7 in the wide, intermediate and deepregions, that span approximately 50%, 15% and 35% of the total area. The multi-wavelength photom-etry includes broad-band data from UV (U band from KPNO and LBC), optical (HST/ACS F435W,F606W, F775W, F814W, and F850LP), near-to-mid IR (HST/WFC3 F105W, F125W, F140W andF160W, Subaru/MOIRCS Ks, CFHT/Megacam K, andSpitzer/IRAC 3.6, 4.5, 5.8, 8.0μm) and far IR(Spitzer/MIPS 24μm, HERSCHEL/PACS 100 and 160μm, SPIRE 250, 350 and 500μm) observations.In addition, the catalog also includes, optical medium-band data (R∼50) in 25 consecutive bands,λ= 500 to 950 nm, from the SHARDS survey and WFC3 IR spectroscopic observations with theG102 and G141 grisms (R∼210 and 130). The use of higher spectral resolution data to estimate pho-tometric redshifts provides very high, and nearly uniform, precision fromz= 0−2.5. The comparisonto 1,485 good quality spectroscopic redshifts up toz∼3 yields ∆z/(1+zspec)=0.0032 and an outlierfraction ofη=4.3%. In addition to the multi-band photometry, we release added-value catalogs withemission line fluxes, stellar masses, dust attenuations, UV- and IR-based star formation rates andrest-frame colors.

Guillermo Barro↗
NASA NTRSDate not supplied

3D Modeling of Solar-Type Stars to Characterize Stellar Jitter

Detection of Earth-mass planets requires measurements of radial velocity with extreme precision. To capture the tiny disturbances caused by a planet's motion, it is necessary to understand and characterize the host star’s turbulent dynamics in order to apply proper filtering to the observational data. We take advantage of current computational and technological capabilities to develop 3D realistic models of the stellar subsurface convection and atmospheres and thereby estimate the photospheric jitter. We have identified an initial set of target stars, obtained initial conditions using the MESA code, and obtained initial 3D radiative models of the stellar surfaces and atmospheres with a spatial resolution of 50km. We present initial 3D radiative hydrodynamic model results of the planet-hosting star HD209458.

SMD↗
NASA NTRS2021

The orbit and stellar masses of the archetype colliding-wind binary WR 140

We present updated orbital elements for the Wolf–Rayet (WR) binary WR 140 (HD 193793; WC7pd + O5.5fc). The new orbital elements were derived using previously published measurements along with 160 new radial velocity measurements across the 2016 periastron passage of WR 140. Additionally, four new measurements of the orbital astrometry were collected with the CHARA Array. With these measurements, we derive stellar masses of M(WR)=10.31±0.45Mꙩ and M(O)=29.27±1.14Mꙩ⁠. We also include a discussion of the evolutionary history of this system from the Binary Population and Spectral Synthesis model grid to show that this WR star likely formed primarily through mass-loss in the stellar winds, with only a moderate amount of mass lost or transferred through binary interactions.

Joshua D. Thomas↗
NASA NTRS2020

Status of NASA’s stellar astrometry testbeds for exoplanet detection: Science and technology overview

Accurate measurement of exoplanetary masses is a critical step in addressing key aspects of NASA's science vision. Measuring masses of Earth-analogs around FGK stars out to 10 pc requires sub-microarcsecond astrometric accuracy, which is not within the capabilities of current instrumentation. Thus, new technology will be required to build an astrometric instrument capable of achieving such performance. This will immediately empower the possibility for dedicated astrometric missions, and perhaps most enticing, it will enable astrometric observing modes to be added (with relatively low cost and impact) to any mission boasting a sufficiently stable direct imaging platform. In this paper, we provide an overview of the scientifi?c goals and technology utilized on two of NASA's astrometry testbeds dedicated to advancing stellar astrometry for exoplanet detection. The ?first one, located at the Jet Propulsion Laboratory (JPL), is dedicated to imaging stellar astrometry on sparse ?fields. The goal of this testbed is to mature the Diffractive Pupil (DP) technology to TRL-5, demonstrating high-?fidelity performance in a relevant environment. This testbed operates in a vacuum tank at the High Contrast Imaging Testbed (HCIT) at JPL. The second testbed, located at NASA Ames Research Center, is dedicated to advancing narrow angle relative astrometry to detect exoplanets around nearby binary stars. The key technology in this testbed is a DP specially designed to measure the angle between two sources on the sky. This testbed operates in air and aims to bring this technology to TRL-4.

Guyon, Olivier↗
NASA NTRS2023

Protoplanetary Disk Science with the Orbiting Astronomical Satellite Investigating Stellar Systems (OASIS) Observatory

The Orbiting Astronomical Satellite for Investigating Stellar Systems (OASIS) is a NASA Astrophysics MIDEX-class mission concept, with the stated goal of Following water from galaxies, through protostellar systems, to Earth’s oceans. This paper details the protoplanetary disk science achievable with OASIS. OASIS’s suite of heterodyne receivers allow for simultaneous, high spectral resolution observations of water emission lines The Orbiting Astronomical Satellite for Investigating Stellar Systems (OASIS) is a NASA Astrophysics MIDEX-class mission concept, with the stated goal of Following water from galaxies, through protostellar systems, to Earth’s oceans. This paper details the protoplanetary disk science achievable with OASIS. OASIS’s suite of heterodyne receivers allow for simultaneous, high spectral resolution observations of water emission lines HD in 100+ disks, allowing for the most accurate determination of total protoplanetary disk gas mass to date. When combined with the contemporaneous water observations, the HD detection will also allow us to trace the evolution of water vapor across evolutionary stages. These observations will enable OASIS to characterize the time development of the water distribution and the role water plays in the process of planetary system formation.

Kamber R Schwarz↗
NASA NTRS2020

An Evolutionary System of Mineralogy. Part I: Stellar Mineralogy (>13 to 4.6 Ga)

Minerals preserve records of the physical, chemical, and biological histories of their origins and subsequent alteration, and thus provide a vivid narrative of the evolution of Earth and other worlds through billions of years of cosmic history. Mineral properties, including trace and minor elements, ratios of isotopes, solid and fluid inclusions, external morphologies, and other idiosyncratic attributes, represent information that points to specific modes of formation and subsequent environmental histories—information essential to understanding the co-evolving geosphere and biosphere. This perspective suggests an opportunity to amplify the existing system of mineral classification, by which minerals are defined solely on idealized end-member chemical compositions and crystal structures. Here we present the first in a series of contributions to explore a complementary evolutionary system of mineralogy—a classification scheme that links mineral species to their paragenetic modes. The earliest stage of mineral evolution commenced with the appearance of the first crystals in the universe at >13 Ga and continues today in the expanding, cooling atmospheres of countless evolved stars, which host the high-temperature (T > 1000 K), low-pressure (P < 10-2 atm) condensation of refractory minerals and amorphous phases. Most stardust is thought to originate in three distinct processes in carbon- and/or oxygen-rich mineral-forming stars: (1) condensation in the cooling, expanding atmospheres of asymptotic giant branch stars; (2) during the catastrophic explosions of supernovae, most commonly core collapse (Type II) supernovae; and (3) classical novae explosions, the consequence of runaway fusion reactions at the surface of a binary white dwarf star. Each stellar environment imparts distinctive isotopic and trace element signatures to the micro- and nanoscale stardust grains that are recovered from meteorites and micrometeorites collected on Earth’s surface, by atmospheric sampling, and from asteroids and comets. Although our understanding of the diverse mineral-forming environments of stars is as yet incomplete, we present a preliminary catalog of 41 distinct natural kinds of stellar minerals, representing 22 official International Mineralogical Association (IMA) mineral species, as well as 2 as yet unapproved crystalline phases and 3 kinds of non-crystalline condensed phases not codified by the IMA.

Robert M. Hazen↗
NASA NTRS2024

JWST Mid-Infrared Spectroscopy Resolves Gas, Dust, and Ice in Young Stellar Objects in the Large Magellanic Cloud

In this work, we present spectra of 11 young stellar objects (YSOs) taken with the Mid-Infrared Instrument (MIRI) / Medium Resolution Spectroscopy (MRS) instrument onboard the James Webb Space Telescope (JWST). The YSOs are located in the N79 region of the Large Magellanic Cloud (LMC), an active star forming region with hundreds of Spitzer - and Herschel-identified YSOs and host to super star cluster (SSC) candidate H72.97-69.39. The three giant molecular clouds (GMCs) in N79 (East, West, and South) have varying star formation rates and stellar populations. MRS follow-up observations of four Spitzer -identified YSOs in N79 East, West, and South reveal that what seemed to be a single, massive YSO is actually a cluster of YSOs. We discuss the emission and absorption lines of six YSOs which have complete or almost-complete spectral coverage from 4.9 – 27.9 µm. YSO Y3, located in N79 East, is the youngest source in this study and likely to be less than 10,000 years old inferred from the prominent CH 4 , NH 3 , CH 3 OH, CH 3 OCHO, and CO 2 ice absorption features. The most luminous source is the central ionizing YSO of SSC H72.97-69.39, Y4, which has dozens of fine-structure and H 2 emission lines. Unlike the other YSOs in this work, Y4 has no polyaromatic hydrocarbon (PAH) emission lines due to the intense ionizing radiation destroying these large carbon chain molecules. The mass accretion rate based on H I (7-6) line luminosity of YSOs Y1, Y2, Y4, and Y9 range between 1.22 × 10 −4 – 1.89 × 10 −2 M ⊙ yr −1 For the first time in the mid-infrared, we are able to resolve individual high-mass protostars forming in small clusters in an extra-galactic environment like the LMC.

Omnarayni Nayak↗
NASA NTRS2023

High Tide or Riptide on the Cosmic Shoreline? A Water-Rich Atmosphere or Stellar Contamination for the Warm Super-Earth GJ 486b from JWST Observations

Planets orbiting M-dwarf stars are prime targets in the search for rocky exoplanet atmospheres. The small size of M dwarfs renders their planets exceptional targets for transmission spectroscopy, facilitating atmospheric characterization. However, it remains unknown whether their host stars’ highly variable extreme-UV radiation environments allow atmospheres to persist. With JWST, we have begun to determine whether or not the most favorable rocky worlds orbiting M dwarfs have detectable atmospheres. Here, we present a 2.8—5.2 µm JWST NIRSpec/G395H transmission spectrum of the warm (700 K, 40.3× Earth’s insolation) super-Earth GJ 486b (1.3 R⊕ and 3.0 M⊕). The measured spectrum from our two transits of GJ 486b deviates from a flat line at 2.2 − 3.3σ, based on three independent reductions. Through a combination of forward and retrieval models, we determine that GJ 486b either has a water-rich atmosphere (with the most stringent constraint on the retrieved water abundance of H2O > 10% to 2σ) or the transmission spectrum is contaminated by water present in cool unocculted starspots. We also find that the measured stellar spectrum is best fit by a stellar model with cool starspots and hot faculae. While both retrieval scenarios provide equal quality fits (χ2ν = 1.0) to our NIRSpec/G395H observations, shorter wavelength observations can break this degeneracy and reveal if GJ 486b sustains a water-rich atmosphere.

JWST↗