Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Planetary”

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 1,513 records · Page 84
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Water masers in W43A: Early morphological changes of a future planetary nebula

We present the distribution patterns of H{sub 2}O maser features in the “water fountain” source (WF) W43A and show that they are closely related to the early morphological changes in a planetary nebula (PN). Using the Very Long Baseline Array, we have detected H{sub 2}O maser features in W43A in 13 epochs across >10 yr. W43A is the only WF that has been observed for over a decade. We introduce a new cavity model scenario—a halo with a bipolar evacuated volume that has a partially enhanced wall—and compare it with the “traditional” precessing jet model particularly in terms of explaining the bow-shaped distribution patterns of H{sub 2}O maser features in the most recent epochs and their temporal evolution. Long-term observations show that the distribution patterns require more than a single jet to form. Moreover, we have identified six groups of H{sub 2}O maser features at both the redshifted and blueshifted sides with point symmetry. The six groups are believed to correspond to periodic mass profiles in the envelope and have recorded the mass-loss history. Together with a geometric similarity to the mid-infrared morphology of W43A, the results suggest that H{sub 2}O masers can be used to trace the inner morphology and rapid temporal changes in evolved stars, especially where the PN shaping has just started.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Time-variable non-thermal emission in the planetary nebula IRAS 15103–5754

The beginning of photoionization marks the transition between the post-AGB and planetary nebula (PN) phases of stars with masses ≲8 M {sub ⊙}. This critical phase is difficult to observe, as it lasts only a few decades. The combination of jets and magnetic fields, the key agents of PN shaping, could give rise to synchrotron emission, but this has never been observed before in any PNe, since free–free emission from the ionized gas is expected to dominate its radio spectrum. In this paper we report radio continuum observations taken with the ATCA between 1 and 46 GHz of the young PN IRAS 15103–5754. Our observations in 2010–2011 show non-thermal emission compatible with synchrotron emission from electrons accelerated at a shock with spectral index α≃−0.54. However, in 2012, the spectral index α≃−0.28 is no longer compatible with synchrotron emission in these types of processes. Several hypotheses are discussed to explain this change. The more plausible ones are related to the presence of the newly photoionized region in this young PN: either energy loss of electrons due to Coulomb collisions with the plasma, or selective suppression of synchrotron radiation due to the Razin effect. We postulate that the observed flattening of non-thermal radio spectra could be a hallmark identifying the beginning of the PN phase.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

The chemistry of planetary nebulae in the outer regions of M31

We present spectroscopy of nine planetary nebulae (PNe) in the outskirts of M31, all but one obtained with the 10.4 m GTC telescope. These sources extend our previous study of the oxygen abundance gradient of M31 to galactocentric radii as large as 100 kpc. None of the targets are bona fide members of a classical, metal-poor, and ancient halo. Two of the outermost PNe have solar oxygen abundances, as well as radial velocities consistent with the kinematics of the extended disk of M31. The other PNe have a slightly lower oxygen content ([O/H] ∼−0.4) and in some cases large deviations from the disk kinematics. These PNe support the current view that the external regions of M31 are the result of a complex interaction and merger process, with evidence for a widespread population of solar-metallicity stars produced in a starburst that occurred ∼2 Gyr ago.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

High-resolution imaging of NGC 2346 with GSAOI/GeMS: Disentangling the planetary nebula molecular structure to understand its origin and evolution

We present high spatial resolution (≈60–90 mas) images of the molecular hydrogen emission in the planetary nebula (PN) NGC 2346. The data were acquired during the system verification of the Gemini Multi-conjugate Adaptive Optics System + Gemini South Adaptive Optics Imager. At the distance of NGC 2346, 700 pc, the physical resolution corresponds to ≈56 AU, which is slightly higher than an [N ii] image of NGC 2346 that was obtained with the Hubble Space Telescope/WFPC2. With this unprecedented resolution, for the first time we were able to study the structure of the H{sub 2} gas within the nebula in detail. We found it to be composed of knots and filaments, which at a lower resolution had appeared to be a uniform torus of material. We explain how the formation of the clumps and filaments in this PN are consistent with a mechanism in which a central hot bubble of nebular gas surrounding the central star has been depressurized, and the thermal pressure of the photoionized region drives the fragmentation of the swept-up shell.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

INFRARED TWO-COLOR DIAGRAMS FOR AGB STARS, POST-AGB STARS, AND PLANETARY NEBULAE

We present various infrared two-color diagrams (2CDs) for asymptotic giant branch (AGB) stars, post-AGB stars, and Planetary Nebulae (PNe) and investigate possible evolutionary tracks. We use catalogs from the available literature for the sample of 4903 AGB stars (3373 O-rich; 1168 C-rich; 362 S-type), 660 post-AGB stars (326 post-AGB; 334 pre-PN), and 1510 PNe in our Galaxy. For each object in the catalog, we cross-identify the IRAS, AKARI, Midcourse Space Experiment, and 2MASS counterparts. The IR 2CDs can provide useful information about the structure and evolution of the dust envelopes as well as the central stars. To find possible evolutionary tracks from AGB stars to PNe on the 2CDs, we investigate spectral evolution of post-AGB stars by making simple but reasonable assumptions on the evolution of the central star and dust shell. We perform radiative transfer model calculations for the detached dust shells around evolving central stars in the post-AGB phase. We find that the theoretical dust shell model tracks using dust opacity functions of amorphous silicate and amorphous carbon roughly coincide with the densely populated observed points of AGB stars, post-AGB stars, and PNe on various IR 2CDs. Even though some discrepancies are inevitable, the end points of the theoretical post-AGB model tracks generally converge in the region of the observed points of PNe on most 2CDs.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

SOLAR-WIND ION-DRIVEN X-RAY EMISSION FROM COMETARY AND PLANETARY ATMOSPHERES: MEASUREMENTS AND THEORETICAL PREDICTIONS OF CHARGE-EXCHANGE CROSS-SECTIONS AND EMISSION SPECTRA FOR O{sup 6+} + H{sub 2}O, CO, CO{sub 2}, CH{sub 4}, N{sub 2}, NO, N{sub 2}O, AND Ar

Relevant to modeling and understanding X-ray emission from cometary and planetary atmospheres, total cross-sections for 1.17 and 2.33 keV/u O{sup 6+} colliding with H{sub 2}O, CO, CO{sub 2}, CH{sub 4}, N{sub 2}, NO, N{sub 2}O, and Ar have been measured for the processes of single, double, and triple charge exchanges. Using these measurements as benchmarks, synthetic emission spectra spanning the X-ray, UV, and visible range have been calculated based on theoretical treatment of the transfer of between one and six electrons from the target neutrals to the projectile ion, followed by radiative and non-radiative decay of the highly excited states produced in these collisions. The results help add to the base of knowledge required to simulate ion-neutral processes in astrophysical environments; refine the present understanding of these fundamental atomic processes; and guide future observations, laboratory measurements, and theoretical predictions.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2015

DETECTING AND CONSTRAINING N{sub 2} ABUNDANCES IN PLANETARY ATMOSPHERES USING COLLISIONAL PAIRS

Characterizing the bulk atmosphere of a terrestrial planet is important for determining surface pressure and potential habitability. Molecular nitrogen (N{sub 2}) constitutes the largest fraction of Earth's atmosphere and is likely to be a major constituent of many terrestrial exoplanet atmospheres. Due to its lack of significant absorption features, N{sub 2} is extremely difficult to remotely detect. However, N{sub 2} produces an N{sub 2}–N{sub 2} collisional pair, (N{sub 2}){sub 2}, which is spectrally active. Here we report the detection of (N{sub 2}){sub 2} in Earth's disk-integrated spectrum. By comparing spectra from NASA's EPOXI mission to synthetic spectra from the NASA Astrobiology Institute's Virtual Planetary Laboratory three-dimensional spectral Earth model, we find that (N{sub 2}){sub 2} absorption produces a ∼35% decrease in flux at 4.15 μm. Quantifying N{sub 2} could provide a means of determining bulk atmospheric composition for terrestrial exoplanets and could rule out abiotic O{sub 2} generation, which is possible in rarefied atmospheres. To explore the potential effects of (N{sub 2}){sub 2} in exoplanet spectra, we used radiative transfer models to generate synthetic emission and transit transmission spectra of self-consistent N{sub 2}–CO{sub 2}–H{sub 2}O atmospheres, and analytic N{sub 2}–H{sub 2} and N{sub 2}–H{sub 2}–CO{sub 2} atmospheres. We show that (N{sub 2}){sub 2} absorption in the wings of the 4.3 μm CO{sub 2} band is strongly dependent on N{sub 2} partial pressures above 0.5 bar and can significantly widen this band in thick N{sub 2} atmospheres. The (N{sub 2}){sub 2} transit transmission signal is up to 10 ppm for an Earth-size planet with an N{sub 2}-dominated atmosphere orbiting within the habitable zone of an M5V star and could be substantially larger for planets with significant H{sub 2} mixing ratios.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

PHOTOMETRY OF THE STINGRAY NEBULA (V839 ARA) FROM 1889 TO 2015 ACROSS THE IONIZATION OF ITS PLANETARY NEBULA

Up until around 1980, the Stingray was an ordinary B1 post-AGB star, but then it suddenly sprouted bright emission lines like in a planetary nebula (PN), and soon after this the Hubble Space Telescope (HST) discovered a small PN around the star, so apparently we have caught a star in the act of ionizing a PN. We report here on a well-sampled light curve from 1889 to 2015, with unique coverage of the prior century plus the entire duration of the PN formation plus three decades of its aftermath. Surprisingly, the star anticipated the 1980s ionization event by declining from B = 10.30 in 1889 to B = 10.76 in 1980. Starting in 1980, the central star faded fast, at a rate of 0.20 mag year{sup −1}, reaching B = 14.64 in 1996. This fast fading is apparently caused by the central star shrinking in size. From 1994 to 2015, the V-band light curve is almost entirely from the flux of two bright [O iii] emission lines from the unresolved nebula, and it shows a consistent decline at a rate of 0.090 mag year{sup −1}. This steady fading (also seen in the radio and infrared) has a timescale equal to that expected for ordinary recombination within the nebula, immediately after a short-duration ionizing event in the 1980s. We are providing the first direct measure of the rapidly changing luminosity of the central star on both sides of a presumed thermal pulse in 1980, with this providing a strong and critical set of constraints, and these are found to sharply disagree with theoretical models of PN evolution.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

DISCOVERY OF COLLIMATED BIPOLAR OUTFLOWS IN THE PLANETARY NEBULA TH 2-A

We present a comprehensive set of spatially resolved, integral field spectroscopic mapping of the Wolf–Rayet planetary nebula Th 2-A, obtained using the Wide Field Spectrograph on the Australian National University 2.3-m telescope. Velocity-resolved Hα channel maps with a resolution of 20 km s{sup −1} allow us to identify different kinematic components within the nebula. This information is used to develop a three-dimensional morpho-kinematic model of the nebula using the interactive kinematic modeling tool shape. These results suggest that Th 2-A has a thick toroidal shell with an expansion velocity of 40 ± 10 km s{sup −1}, and a thin prolate ellipsoid with collimated bipolar outflows toward its axis reaching velocities in the range of 70–110 km s{sup −1}, with respect to the central star. The relationship between its morpho-kinematic structure and peculiar [WO]-type stellar characteristics deserves further investigation.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Chemical abundances of planetary nebulae in the substructures of M31

We present deep spectroscopy of planetary nebulae (PNe) that are associated with the substructures of the Andromeda Galaxy (M31). The spectra were obtained with the Optical System for Imaging and low-intermediate-Resolution Integrated Spectroscopy spectrograph on the 10.4 m Gran Telescopio Canarias. Seven targets were selected for the observations, three in the Northern Spur and four associated with the Giant Stream. The most distant target in our sample, with a rectified galactocentric distance ⩾ 100 kpc, was the first PN discovered in the outer streams of M31. The [O iii] λ4363 auroral line is well detected in the spectra of all targets, enabling electron temperature determination. Ionic abundances are derived based on the [O iii] temperatures, and elemental abundances of helium, nitrogen, oxygen, neon, sulfur, and argon are estimated. The relatively low N/O and He/H ratios, as well as abundance ratios of α-elements, indicate that our target PNe might belong to populations as old as ∼2 Gyr. Our PN sample, including the current seven and the previous three observed by Fang et al., have rather homogeneous oxygen abundances. The study of abundances and the spatial and kinematical properties of our sample leads to the tempting conclusion that their progenitors might belong to the same stellar population, which hints at a possibility that the Northern Spur and the Giant Stream have the same origin. This may be explained by the stellar orbit proposed by Merrett et al. Judging from the position and kinematics, we emphasize that M32 might be responsible for the two substructures. Deep spectroscopy of PNe in M32 will help to assess this hypothesis.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

SPITZER SEARCH FOR DUST DISKS AROUND CENTRAL STARS OF PLANETARY NEBULAE

Two types of dust disks have been discovered around white dwarfs (WDs): small dust disks within the Roche limits of their WDs and large dust disks around hot WDs extending to radial distances of 10-10{sup 2} AU. The majority of the latter WDs are central stars of planetary nebulae (CSPNs). We have therefore used archival Spitzer Infrared Array Camera (IRAC) and Multiband Imaging Photometer for Spitzer (MIPS) observations of PNs to search for CSPNs with IR excesses and to make a comparative investigation of dust disks around stars at different evolutionary stages. We have examined available images of 72 resolved PNs in the Spitzer archive and found 56 of them large enough for the CSPN to be resolved from the PN. Among these, only 42 CSPNs are visible in IRAC and/or MIPS images and selected for photometric measurements. From the spectral energy distributions (SEDs) of these CSPNs, we find 19 cases with clear IR excess. Of these, seven are [WC]-type stars, two have apparent visual companions that account for the observed excess emission, two are symbiotic CSPNs, and in eight cases the IR excess originates from an extended emitter, likely a dust disk. For some of these CSPNs, we have acquired follow-up Spitzer MIPS images, Infrared Spectrograph spectra, and Gemini NIRI and Michelle spectroscopic observations. The SEDs and spectra show a great diversity in the emission characteristics of the IR excesses, which may imply different mechanisms responsible for the excess emission. For CSPNs whose IR excesses originate from dust continuum, the most likely dust production mechanisms are (1) breakup of bodies in planetesimal belts through collisions and (2) formation of circumstellar dust disks through binary interactions. A better understanding of post-asymptotic giant branch binary evolution as well as debris disk evolution along with its parent star is needed to distinguish between these different origins. Future observations to better establish the physical parameters of the dust disks and the presence of companions are needed for models to discern between the possible dust production mechanisms.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Chemical abundances and dust in the halo planetary nebula K648 IN M15: its origin and evolution based on an analysis of multiwavelength data

We report on an investigation of the extremely metal-poor and C-rich planetary nebula (PN) K648 in M15 using the UV to far-infrared data obtained using Subaru, the Hubble Space Telescope, the Far Ultraviolet Spectroscopic Explorer, Spitzer, and Herschel. We determined the nebular abundances of 10 elements. The enhancement of F ([F/H] = +0.96) is comparable to that of the halo PN BoBn1. The central stellar abundances of seven elements are determined. The stellar C/O ratio is similar to the nebular C/O ratios from recombination lines and from collisionally excited lines (CELs) within error, and the stellar Ne/O ratio is also close to the nebular CEL Ne/O ratio. We found evidence of carbonaceous dust grains and molecules including Class B 6–9 and 11.3 μm polycyclic aromatic hydrocarbons and the broad 11 μm feature. The profiles of these bands are similar to those of the C-rich halo PNe H4-1 and BoBn1. Based on the theoretical model, we determined the physical conditions of the gas and dust and their masses, i.e., 0.048 and 4.95 × 10{sup −7} M{sub ⊙}, respectively. The observed chemical abundances and gas mass are in good agreement with an asymptotic giant branch nucleosynthesis model prediction for stars with an initial 1.25 M{sub ⊙} plus a 2.0 × 10{sup −3} M{sub ⊙} partial mixing zone (PMZ) and stars with an initial mass of 1.5 M{sub ⊙} without a PMZ. The core mass of the central star is approximately 0.61–0.63 M{sub ⊙}. K648 is therefore likely to have evolved from a progenitor that experienced coalescence or tidal disruption during the early stages of evolution, and became a ∼1.25–1.5 M{sub ⊙} blue straggler.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

THE ABUNDANCES OF LIGHT NEUTRON-CAPTURE ELEMENTS IN PLANETARY NEBULAE. III. THE IMPACT OF NEW ATOMIC DATA ON NEBULAR SELENIUM AND KRYPTON ABUNDANCE DETERMINATIONS

The detection of neutron(n)-capture elements in several planetary nebulae (PNe) has provided a new means of investigating s-process nucleosynthesis in low-mass stars. However, a lack of atomic data has inhibited accurate trans-iron element abundance determinations in astrophysical nebulae. Recently, photoionization (PI) and recombination data were determined for Se and Kr, the two most widely detected n-capture elements in nebular spectra. We have incorporated these new data into the photoionization code Cloudy. To test the atomic data, numerical models were computed for 15 PNe that exhibit emission lines from multiple Kr ions. We found systematic discrepancies between the predicted and observed emission lines that are most likely caused by inaccurate PI and recombination data. These discrepancies were removed by adjusting the Kr{sup +}–Kr{sup 3+} PI cross sections within their cited uncertainties and the dielectronic recombination rate coefficients by slightly larger amounts. From grids of models spanning the physical conditions encountered in PNe, we derive new, broadly applicable ionization correction factor (ICF) formulae for calculating Se and Kr elemental abundances. The ICFs were applied to our previous survey of near-infrared [Kr iii] and [Se iv] emission lines in 120 PNe. The revised Se and Kr abundances are 0.1–0.3 dex lower than former estimates, with average values of [Se/(O, Ar)] = 0.12 ± 0.27 and [Kr/(O, Ar)] = 0.82 ± 0.29, but correlations previously found between their abundances and other nebular and stellar properties are unaffected. We also find a tendency for high-velocity PNe that can be associated with the Galactic thick disk to exhibit larger s-process enrichments than low-velocity PNe belonging to the thin-disk population.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

THE EFFECTS OF SNOWLINES ON C/O IN PLANETARY ATMOSPHERES

The C/O ratio is predicted to regulate the atmospheric chemistry in hot Jupiters. Recent observations suggest that some exoplanets, e.g., Wasp 12-b, have atmospheric C/O ratios substantially different from the solar value of 0.54. In this Letter, we present a mechanism that can produce such atmospheric deviations from the stellar C/O ratio. In protoplanetary disks, different snowlines of oxygen- and carbon-rich ices, especially water and carbon monoxide, will result in systematic variations in the C/O ratio both in the gas and in the condensed phases. In particular, between the H{sub 2}O and CO snowlines most oxygen is present in icy grains-the building blocks of planetary cores in the core accretion model-while most carbon remains in the gas phase. This region is coincidental with the giant-planet-forming zone for a range of observed protoplanetary disks. Based on standard core accretion models of planet formation, gas giants that sweep up most of their atmospheres from disk gas outside of the water snowline will have a C/O {approx} 1, while atmospheres significantly contaminated by evaporating planetesimals will have a stellar or substellar C/O when formed at the same disk radius. The overall metallicity will also depend on the atmosphere formation mechanism, and exoplanetary atmospheric compositions may therefore provide constraints on where and how a specific planet formed.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

SULFUR- AND SILICON-BEARING MOLECULES IN PLANETARY NEBULAE: THE CASE OF M2-48

Molecular-line observations of the bipolar planetary nebula (PN) M2-48 have been conducted using the Sub-Millimeter Telescope and the 12 m antenna of the Arizona Radio Observatory at 1, 2, and 3 mm. M2-48 is estimated to be ∼4800 yr old, midway through the PN evolutionary track. SiO and SO{sub 2} were detected in this source—the first identification of either molecule in a PN. CN, HCN, HNC, CS, SO, HCO{sup +}, N{sub 2}H{sup +}, and several {sup 13}C isotopologues such as {sup 13}CN, H{sup 13}CN, and H{sup 13}CO{sup +} were also observed toward this object. A radiative transfer analysis of multiple SiO transitions indicates a gas kinetic temperature of T {sub K} ∼ 55 K and a density of n(H{sub 2}) ∼ 9 × 10{sup 5} cm{sup –3} in M2-48, in agreement with previous CS and CO modeling. After CO, CN, and SO were found to be the most prevalent molecules in this nebula, with fractional abundances, relative to H{sub 2}, of f ∼ 3.8 × 10{sup –7} and 2.4 × 10{sup –7}, respectively. SO{sub 2} and HCN are also abundant, with f ∼ 1.2 × 10{sup –7}, indicating an [SO]/[SO{sub 2}] ratio of ∼2. Relatively high ion abundances were measured in M2-48 as well, with f ∼ 10{sup –7} for both HCO{sup +} and N{sub 2}H{sup +}. An [HCN]/[HNC] ratio of ∼2 was determined, as typically observed in other PNe, independent of age. The high abundances of SO and SO{sub 2}, along with the presence of SiO with f ∼ 2.9 × 10{sup –8}, suggest O/C > 1 in this source; furthermore, the prevalence of CN and N{sub 2}H{sup +} indicates nitrogen enrichment. The {sup 12}C/{sup 13}C ratio of ∼3 in the nebula was also established. These factors indicate hot-bottom burning occurred in the progenitor star of M2-48, suggesting an initial mass > 4 M {sub ☉}.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

AN EXTREME HIGH-VELOCITY BIPOLAR OUTFLOW IN THE PRE-PLANETARY NEBULA IRAS 08005-2356

We report interferometric mapping of the bipolar pre-planetary nebula IRAS 08005-2356 (I 08005) with an angular resolution of ∼1″–5″, using the Submillimeter Array, in the {sup 12}CO J = 2–1, 3–2, {sup 13}CO J = 2–1, and SiO J = 5–4 (v = 0) lines. Single-dish observations, using the SMT 10 m, were made in these lines as well as in the CO J = 4–3 and SiO J = 6–5 (v = 0) lines. The line profiles are very broad, showing the presence of a massive (>0.1 M{sub ⊙}), extreme high velocity outflow (V ∼ 200 km s{sup −1}) directed along the nebular symmetry axis derived from the Hubble Space Telescope imaging of this object. The outflow's scalar momentum far exceeds that available from radiation pressure of the central post-AGB star, and it may be launched from an accretion disk around a main-sequence companion. We provide indirect evidence for such a disk from its previously published, broad Hα emission profile, which we propose results from Lyβ emission generated in the disk followed by Raman-scattering in the innermost regions of a fast, neutral wind.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

Metagenomic Methods for Addressing NASA's Planetary Protection Policy Requirements on Future Missions: A Workshop Report

Molecular biology methods and technologies have advanced substantially over the past decade. These new molecular methods should be incorporated among the standard tools of planetary protection (PP) and could be validated for incorporation by 2026. To address the feasibility of applying modern molecular techniques to such an application, NASA conducted a technology workshop with private industry partners, academics, and government agency stakeholders, along with NASA staff and contractors. The technical discussions and presentations of the Multi-Mission Metagenomics Technology Development Workshop focused on modernizing and supplementing the current PP assays. The goals of the workshop were to assess the state of metagenomics and other advanced molecular techniques in the context of providing a validated framework to supplement the bacterial endospore-based NASA Standard Assay and to identify knowledge and technology gaps. In particular, workshop participants were tasked with discussing metagenomics as a stand-alone technology to provide rapid and comprehensive analysis of total nucleic acids and viable microorganisms on spacecraft surfaces, thereby allowing for the development of tailored and cost-effective microbial reduction plans for each hardware item on a spacecraft. Workshop participants recommended metagenomics approaches as the only data source that can adequately feed into quantitative microbial risk assessment models for evaluating the risk of forward (exploring extraterrestrial planet) and back (Earth harmful biological) contamination. Participants were unanimous that a metagenomics workflow, in tandem with rapid targeted quantitative (digital) PCR, represents a revolutionary advance over existing methods for the assessment of microbial bioburden on spacecraft surfaces. The workshop highlighted low biomass sampling, reagent contamination, and inconsistent bioinformatics data analysis as key areas for technology development. Finally, it was concluded that implementing metagenomics as an additional workflow for addressing concerns of NASA's robotic mission will represent a dramatic improvement in technology advancement for PP and will benefit future missions where mission success is affected by backward and forward contamination.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2023

Spectroscopic survey of faint planetary-nebula nuclei – II. The subdwarf O central star of Fr 2-30

Fr 2-30 = PN? G126.8−15.5 is a faint emission nebula, hosting a 14th-mag central star that we identify here for the first time. Deep Hα and [O III ] images reveal a roughly elliptical nebula with dimensions of at least 22 arcmin × 14 arcmin, fading into a surrounding network of even fainter emission. Optical spectrograms of the central star show it to have a subdwarf O spectral type, with a Gaia parallax distance of 890 pc. A model-atmosphere analysis gives parameters of T eff = 60 000 K, log g = 6.0, and a low helium content of n He /n H = 0.0017. The location of the central star in the log g–T eff plane is inconsistent with a post-asymptotic-giant-branch evolutionary status. Two alternatives are that it is a helium-burning post-extreme-horizontal-branch object, or a hydrogen-burning post-red-giant-branch star. In either case, the evolutionary ages are so long that a detectable planetary nebula (PN) should not be present. We find evidence for a variable radial velocity (RV), suggesting that the star is a close binary. However, there are no photometric variations, and the spectral-energy distribution rules out a companion earlier than M2 V. The RVs of the star and surrounding nebula are discordant, and the nebula lacks typical PN morphology. We suggest that Fr 2-30 is a ‘PN mimic’ – the result of a chance encounter between the hot sdO star and an interstellar cloud. However, we note the puzzling fact that there are several nuclei of genuine PNe that are known to be in evolutionary states similar to that of the Fr 2-30 central star.

79 ASTRONOMY AND ASTROPHYSICS↗