Infrared Telescope Research Articles

A new constraint on HCl abundance at the cloud top of Venus

We provided a new constraint on HCl abundance at the cloud top of Venus by infrared spectroscopy using a cross-dispersed high-resolution echelle spectrograph, iSHELL, mounted on the NASA Infrared Telescope Facility (IRTF). This study investigated the inconsistency in HCl abundance between previous ground-based observations and Venus Express solar occultation measurements. Venusian dayside observations at a solar phase angle of ∼90° were conducted during August 6–7, 2018, and August 18–20, 2020 (UT), when the Venusian afternoon and morning sides were visible, respectively. The high spectral resolving power of ∼80,000 and large Doppler shift (∼13 km/s) enabled the measurement of Venusian lines with less contamination by terrestrial lines. We analyzed the H35Cl P(5) and H37Cl P(6) lines at 2775.8 and 2750.1 cm−1, respectively, in the 1–0 band, together with 16O12C18O P- and R-branch lines of the 20001–00001 band, which fell in the same spectral orders as the HCl lines. The 16O12C18O lines were used to derive the cloud top altitude because the upper clouds significantly impacted the retrieval of HCl abundance. The cloud tops had an equatorially symmetric structure. The average altitude was 70.8 ± 0.6 km in the region equatorward of ±30° and decreased toward higher latitudes. The HCl volume mixing ratio was derived as 0.379 ± 0.013 ppm at a probing altitude of 70.6 ± 1.1 km and showed no significant latitudinal dependence within the range of ±70°. A difference of ∼0.02 ppm between 2018 and 2020 would result mainly from temporal variation. The H35Cl/H37Cl abundance ratio was 3.01 ± 0.16, with no prominent latitudinal dependence. The obtained HCl volume mixing ratio agreed with the results of previous ground-based measurements, which were approximately one order of magnitude larger than those derived from Venus Express solar occultation measurements. The systematic uncertainties in our retrieval analysis cannot explain this significant inconsistency. The impact of diffuse light produced from aerosol scattering on the retrieval method for solar occultation measurements should be investigated further to solve this issue.

Surveying the inner structure of massive young stellar objects using L-band spectroscopy

We present results from a high spectral resolution (6 km s-1) survey of five massive protostars in the wavelength range of 2.95 and 3.25 µm, conducted with iSHELL at the InfraRed Telescope Facility (IRTF). Our targets are Mon R2 IRS 2, Mon R2 IRS 3, AFGL 2136, Orion BN and S140 IRS 1. Two of our five targets (Mon R2 IRS 3 and AFGL 2136) show transitions from organic species, with MonR2 IRS 3 showing HCN lines in emission, and AFGL 2136 showing HCN and C2H2 lines in absorption. The velocity of the emission lines of HCN of MonR2 IRS 3A are consistent with CO emission features in lines up to J = 26, as both are red-shifted with respect to the systemic velocity. Carbon monoxide lines also show blue-shifted absorption. This P-Cygni line profile, commonly observed towards massive young stellar objects, is likely due to an expanding shell, which is supported by sub-millimetre velocity maps of HCN. Alternatively HCN emission may arise from the upper layers of a disk photosphere, as has been suggested for the massive protostar AFGL 2591. Absorption lines in AFGL 2136 may either originate in foreground cloud or in the disk photosphere. For a foreground cloud, the data require that the foreground gas only covers the source partially (0.3) at 13 µm. In contrast, absorption lines at 3 and 7 µm require a covering factor of >0.9. Analysing the 13 µm HCN absorption lines in terms of absorption by gas in the photosphere of a disk, results in physical conditions that are consistent over all three vibrational modes. C2H2 absorption lines reveal an increasing temperature and abundance with decreasing wavelength, indicative of a radial abundance gradient. We conclude that the disk model is the best interpretation of the absorption lines of AFGL 2136.

A Census of the 32 Ori Association with Gaia* *Based on observations made with the Gaia mission, the Two Micron All Sky Survey, the Wide-field Infrared Survey Explorer, the LAMOST survey, the Sloan Digital Sky Survey IV, the NASA Infrared Telescope Facility, and Cerro Tololo Inter-American Observatory.

I have used high-precision photometry and astrometry from the third data release of Gaia (DR3) to identify candidate members of the 32 Ori association. Spectral types and radial velocities have been measured for subsets of the candidates using new and archival spectra. For the candidates that have radial velocity measurements, I have used UVW velocities to further constrain their membership, arriving at a final catalog of 169 candidates. I estimate that the completeness of the survey is ∼90% for spectral types of ≲M7 (≳0.06 M ⊙). The histogram of spectral types for the 32 Ori candidates exhibits a maximum at M5 (∼0.15 M ⊙), resembling the distributions measured for other young clusters and associations in the solar neighborhood. The available UVW velocities indicate that the association is expanding, but they do not produce a well-defined kinematic age. Based on their sequences of low-mass stars in color–magnitude diagrams, the 32 Ori association and Upper Centaurus-Lupus/Lower Centaurus-Crux (UCL/LCC) are coeval to within ±1.2 Myr, and they are younger than the β Pic moving group by ∼3 Myr, which agrees with results from previous analysis based on the second data release of Gaia. Finally, I have used mid-IR photometry from the Wide-field Infrared Survey Explorer to check for excess emission from circumstellar disks among the 32 Ori candidates. Disks are detected for 18 candidates, half of which are reported for the first time in this work. The fraction of candidates at ≤M6 that have full, transitional, or evolved disks is , which is consistent with the value for UCL/LCC.

Composition of inner main-belt planetesimals

Aims. We carried out a spectroscopic survey in order to investigate the composition of 64 asteroids of the inner main belt, which are leftovers of the original planetesimals of our Solar System (we call them inner main belt planetesimals or IMBPs). Following published methods, we identified IMBPs in the inverse size versus semimajor axis (α) space, after the removal of all asteroids belonging to collisional families. Methods. We conducted several ground-based observational campaigns of these IMBPs in the visible range at the 1.82 m Asiago telescope, and in the near-infrared range at the Telescopio Nationale Galileo, the Lowell Discovery Telescope, and the NASA InfraRed Telescope Facility telescopes. As several of the identified planetesimals already have spectra published in the literature, we collected all the available data and focused the telescope time to investigate those never observed before, or to complete the 0.45–2.5 μm range spectrum for those for which there is only partial spectral coverage or data with poor signal-to-noise ratio. In this way, we obtained new spectra for 24 IMBPs. Combining new and literature observations, we present spectra for 60 IMBPs in both the visible and near-infrared range, and 4 IMBPs in the visible only. All spectra were classified following well-established taxonomies. We also characterized their spectral absorption bands – when present –, their spectral slopes, and their mineralogy. In addition, we performed curve matching between astronomical and laboratory spectra in order to identify the closest meteorite analog using the RELAB database. Results. The majority of the IMBPs belong to the S-complex; the latter are best matched with ordinary chondrite meteorites, and their olivine/(olivine and pyroxene) abundance ratio is not correlated with the semi-major axis. This result does not support the hypothesis that this ratio increases with heliocentric distance. Furthermore, ~27% of the IMBPs belong to the C-complex, where Ch/Cgh types dominate, meaning that most of the carbonaceous-rich planetesimals were aqueously altered. These are best fitted by CM2 carbonaceous chondrite meteorites. Finally, the remaining IMBPs (~20%) belong to the X-complex, and have various mineralogies and meteorite matches, while a few are end-member classes, including L-, K-, V-, and D- or T-types. Conclusions. Our spectroscopic investigation of IMBPs confirms that silicate-rich bodies dominated the inner main belt where temperature has permitted the condensation of silicate rocks. However, almost all the spectral types are found, with the notable exception of olivine-rich A-types and Q-type asteroids. Their absence, as well as the absence of the R- and O-types among planetesimals, might be due to the rarity of these types among large asteroids. However, the absence of Q-types among primordial planetesimals is expected, as they have undergone surface rejuvenating processes. Therefore, Q-types have relatively young and less weathered surfaces compared to other types. Our results support the hypothesis of compositional mixing in the early Solar System. In particular, the fact that most of the C-complex planetesimals are aqueous altered, and the presence of three D- or T-type asteroids among them indicate that these bodies migrated from beyond 3 au to their current position.

Probing the innermost region of the AU Microscopii debris disc

Context. AU Mic is a young and nearby M-dwarf star harbouring a circumstellar debris disc and one recently discovered planet on an eight-day orbit. Large-scale structures within the disc were also discovered and are moving outwards at high velocity. Aims. We aim to study this system with the highest spatial resolution in order to probe the innermost regions and to search for additional low-mass companions or set detection limits. Methods. The star was observed with two different high-angular resolution techniques probing complementary spatial scales. We obtained new Ks-band sparse aperture masking observations with VLT/SPHERE, which we combined with data from VLT/NACO, VLTI/PIONIER and VLTI/GRAVITY. Results. We did not detect additional close companions within the separation range 0.02–7 au from the parent star. We determined magnitude upper limits for companions of H ~ 9.8 mag within 0.02-0.5 au, Ks ~ 11.2 mag within 0.4–2.4 au, and L ~ 10.7 mag within 0.7–7 au. Using theoretical isochrones, we converted these magnitudes into upper limits on the mass of ~17 Mjup, ~12 Mjup, and ~9 Mjup, respectively. The PIONIER observations also allowed us to determine the angular diameter of AU Mic, θLD = 0.825 ± 0.033stat ± 0.038sys mas, which converts to a linear radius R = 0.862 ± 0.052 R⊙ when combined with the Gaia parallax. Conclusions. We did not detect the newly discovered planets orbiting AU Mic (M < 0.2 Mjup), but we derived upper limit masses for the innermost region of AU Mic. We do not have any detection with a significance beyond 3σ, the most significant signal with PIONIER being 2.9σ and that with SPHERE being 1.6σ. We applied the pyMESS2 code to estimate the detection probability of companions by combining radial velocities, multi-band SPHERE imaging, and our interferometric detection maps. We show that 99% of the companions down to ~0.5 Mjup can be detected within 0.02 au or 1 Mjup down to 0.2 au. The low-mass planets orbiting at ≲0.11 au (≲11 mas) from the star will not be directly detectable with the current adaptive optics (AO) and interferometric instruments because of its close orbit and very high contrast (~10−10 K). It will also be below the angular resolution and contrast limit of the next Extremely Large Telescope Infrared (ELT IR) imaging instruments.

Three-dimensional structure of thermal waves in Venus’ mesosphere from ground-based observations

High spectral resolution observations of Venus were obtained with the TEXES instrument at NASA’s Infrared Telescope Facility. These observations focus on a CO2 absorption feature at 791.4 cm-1 as the shape of this absorption feature can be used to retrieve the vertical temperature profile in Venus’ mesosphere. By scan-mapping the planet, we are able to build up three-dimensional temperature maps of Venus’ atmosphere, covering one Earth-facing hemisphere and an altitude range of 60–83 km. A temperature map from February 12, 2019 clearly shows the three-dimensional structure of a planetary-scale thermal wave. This wave pattern appears strongest in the mid-latitudes of Venus, has a zonal wavenumber of 2–4 and the wave fronts tilt eastward with altitude at an angle of 8–15 degrees per km. This is consistent with a thermal tide propagating upwards from Venus’ upper cloud decks. Ground-based observations provide the opportunity to study Venus’ temperature structure on an ongoing basis.

Infrared Line Emissions from Atoms and Atomic Ions in NGC 7027: Improved Wavelength Determinations for Infrared Metal Lines and a Probable Detection of Zn5+

An infrared L- and M-band spectral survey, performed toward the young planetary nebula NGC 7027 with the iSHELL instrument on NASA’s Infrared Telescope Facility (IRTF), has revealed more than 20 vibrational lines of the molecules HeH+, H2, and CH+ and more than 50 spectral lines of atoms and atomic ions. The present paper focuses on the atomic line emissions, the molecular lines having been discussed in two previous publications. The atomic lines detected with high confidence in the 2.951–5.24 μm region covered (incompletely) by this survey comprise (1) six collisionally excited lines of metal ions that had previously been identified in astrophysical nebulae but for which the present observations provide the most accurate wavelength determinations obtained to date; (2) a spectral line at 4.6895 μm, not previously reported, for which the probable identification is the 4 F 7/2–4 F 9/2 fine-structure transition of [Zn vi]; (3) 39 recombination lines of H and He+, with upper states of principal quantum number up to 38 (H) or 24 (He+); (4) 10 recombination lines of the multielectron species He, C2+, and C3+.

Near-infrared Spectroscopy of the Nucleus of Low-activity Comet P/2016 BA14 during Its 2016 Close Approach

The near-Earth comet P/2016 BA14 (PanSTARRS) is a slow-rotating, nearly dormant object, a likely dynamical twin of 252P/LINEAR, and was recently shown to have a mid-infrared spectrum very dissimilar to other comets. Comet BA14 was also recently selected as one of the backup targets for the ESA’s Comet Interceptor, so a clearer understanding of BA14's modern properties would not just improve our understanding of how comets go dormant but could also aid in planning for a potential spacecraft visit. We present observations of BA14 during its 2016 Earth close approach taken with the NASA Infrared Telescope Facility on two dates, both of which are consistent with direct observations of its nucleus. The reflectance spectrum of BA14 is similar to 67P/Churyumov–Gerasimenko, albeit highly phase-reddened. Thermal emission contaminates the reflectance spectrum at longer wavelengths, which we correct with a new Markov Chain Monte Carlo thermal modeling code. The models suggest that BA14's visible geometric albedo is p V = 0.01–0.03, consistent with radar observations; its beaming parameter is typical for NEOs observed in its geometry; and its reflectance spectrum is red and linear throughout the H and K bands. It appears very much like a “normal” comet nucleus despite its mid-infrared oddities. A slow loss of fine grains as the object’s activity diminished might help to reconcile some of the lines of evidence, and we discuss other possibilities. A spacecraft flyby past BA14 could get closer to the nucleus than with a more active target, and we highlight some science questions that could be addressed with a visit to a (nearly) dormant comet.

The Debiased Compositional Distribution of MITHNEOS: Global Match between the Near-Earth and Main-belt Asteroid Populations, and Excess of D-type Near-Earth Objects

Abstract We report 491 new near-infrared spectroscopic measurements of 420 near-Earth objects (NEOs) collected on the NASA InfraRed Telescope Facility as part of the MIT-Hawaii NEO Spectroscopic Survey. These measurements were combined with previously published data from Binzel et al. and bias-corrected to derive the intrinsic compositional distribution of the overall NEO population, as well as of subpopulations coming from various escape routes (ERs) in the asteroid belt and beyond. The resulting distributions reflect well the overall compositional gradient of the asteroid belt, with decreasing fractions of silicate-rich (S- and Q-type) bodies and increasing fractions of carbonaceous (B-, C-, D- and P-type) bodies as a function of increasing ER distance from the Sun. The close compositional match between NEOs and their predicted source populations validates dynamical models used to identify ERs and argues against any strong composition change with size in the asteroid belt between ∼5 km and ∼100 m. A notable exception comes from the overabundance of D-type NEOs from the 5:2J and, to a lesser extend, the 3:1J and ν 6 ERs, hinting at the presence of a large population of small D-type asteroids in the main belt. Alternatively, this excess may indicate preferential spectral evolution from D-type surfaces to C and P types as a consequence of space weathering, or point to the fact that D-type objects fragment more often than other spectral types in the NEO space. No further evidence for the existence of collisional families in the main belt, below the detection limit of current main-belt surveys, was found in this work.

A comprehensive analysis of WASP-17b’s transmission spectrum from space-based observations

ABSTRACT Due to its 1770 K equilibrium temperature, WASP-17b, a 1.99 RJup, 0.486 MJup exoplanet, sits at the critical juncture between hot and ultra-hot Jupiters. We present its 0.3–5 $\rm{\mu m}$ transmission spectrum, newly obtained with Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) measurements, and, taking advantage of improved analysis techniques, reanalysed HST Space Telescope Imaging Spectrograph and Spitzer Space Telescope Infrared Array Camera observations. We achieve a median precision of 132 ppm, with a mean of 272 ppm across the whole spectrum. We additionally make use of Transiting Exoplanet Survey Satellite (TESS) and ground-based transit observations to refine the orbital period of WASP-17b. To interpret the observed atmosphere, we make use of free and equilibrium chemistry retrievals using the POSEIDON and ATMO retrieval codes, respectively. We detect absorption due to H2O at >7σ and find evidence of absorption due to CO2 at >3σ. We see no evidence of previously detected Na i and K i absorption. Across an extensive suite of retrieval configurations, we find that the data favour a bimodal solution with high- or low-metallicity modes as a result of poor constraints in the optical and demonstrate the importance of using multiple statistics for model selection. Future JWST GTO observations, combined with the presented transmission spectrum, will enable precise constraints on WASP-17b’s atmosphere.

The global thermophysical properties of (433) Eros

We present results from a shape-based, rotationally-resolved thermophysical model of near-Earth asteroid (433) Eros, using reflected and near-IR spectra collected at the NASA Infrared Telescope Facility (IRTF) over 18 nights (25 disk-integrated spectra in total) from 2009 to 2019. The data sample a variety of viewing geometries, illumination angles, and rotational phases and therefore allow us to characterize Eros's surface physical properties in detail, particularly at wavelengths in the thermal near-IR regime (λ > 3.5 μm) that were not measured by the NEAR Shoemaker mission. Eros's shape, spin state, density, albedo, and other physical properties measured by NEAR were incorporated into our model, leaving thermal inertia and surface roughness as free parameters. We find that a thermal inertia range of 100–150 J m−2 K−1 s-1/2 and a roughness crater fraction of 0.3–0.4 with crater opening angle 130° (equivalent adirectional rms slope angle of 32° +/− 4°) fit data from 18 spectra at the 1σ level, but do not fit the remaining 7 spectra. This suggests that Eros's thermal properties vary over its surface, which has important implications for linking remote sensing data to spacecraft measurements of the physical properties of near-Earth asteroids.

A Massive AGB Donor in Scutum X-1: Identification of the First Mira Variable in an X-Ray Binary

Abstract The symbiotic X-ray binary Sct X-1 was suggested to be the first known neutron star accreting from a red supergiant companion. Although known for nearly 50 yr, detailed characterization of the donor remains lacking, particularly due to the extremely high reddening toward the source (A V ≳ 25 mag). Here, we present (i) improved localization of the counterpart using Gaia and Chandra observations, (ii) the first broadband infrared spectrum (≈1–5 μm; R ≈ 2000) obtained with SpeX on the NASA Infrared Telescope Facility, and (iii) the J-band light curve from the Palomar Gattini-IR survey. The infrared spectrum is characterized by (i) deep water absorption features (H2O index ≈ 40%), (ii) strong TiO, VO, and CO features, and (iii) weak/absent CN lines. We show that these features are inconsistent with known red supergiants but suggest an M8-9 III–type O-rich Mira donor star. We report the discovery of large-amplitude (ΔJ ≈ 3.5 mag) periodic photometric variability, suggesting a pulsation period of 621 ± 36 (systematic) ± 8 (statistical) days, which we use to constrain the donor to be a relatively luminous Mira (M K = −8.6 ± 0.3 mag) at a distance of 3.6 − 0.7 + 0.8 kpc. Comparing these characteristics to recent models, we find the donor to be consistent with a ≈3–5 M ⊙ star at an age of ≈0.1–0.3 Gyr. Together, we show that Sct X-1 was previously misclassified as an evolved high-mass X-ray binary; instead, it is an intermediate-mass system with the first confirmed Mira donor in an X-ray binary. We discuss the implications of Mira donors in symbiotic X-ray binaries and highlight the potential of wide-field infrared time-domain surveys and broadband infrared spectroscopy to unveil their demographics.

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

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

ISHELL: a 1–5 micron R = 80,000 Immersion Grating Spectrograph for the NASA Infrared Telescope Facility

iSHELL is a 1.06–5.3 μm high spectral resolution spectrograph built for the 3.2 m NASA Infrared Telescope Facility (IRTF) on Maunakea, Hawaii. Dispersion is accomplished with a silicon immersion grating in order to keep the instrument small enough to be mounted at the Cassegrain focus of the telescope. The white pupil spectrograph produces resolving powers of up to about R ≡ λ/δλ = 80,000 (0.″375 slit). Cross-dispersing gratings mounted in a tiltable mechanism allow observers to select different wavelength ranges and, in combination with a slit wheel and Dekker mechanism, slit widths ranging from 0.″375 to 4.″0 and slit lengths ranging from 5″ to 25″. One Teledyne 2048 × 2048 HAWAII-2RG array is used in the spectrograph, and one Raytheon 512 × 512 Aladdin 2 array is used in a 1–5 μm slit viewer for object acquisition, guiding, and scientific imaging. iSHELL has been in productive regular use on IRTF since first light in 2016 September. In this paper we discuss details of the science case, design, construction and astronomical use of iSHELL.

H-band Light Curves of Milky Way Cepheids via Difference Imaging

Abstract We present H-band light curves of Milky Way classical Cepheids observed as part of the Dark Energy, H 0, and peculiar Velocities using Infrared Light from Supernovae survey with the Wide-Field Infrared Camera on the United Kingdom Infrared Telescope. Due to the crowded nature of these fields caused by defocusing the Camera, we performed difference-imaging photometry by modifying a pipeline originally developed to analyze images from the Transiting Exoplanet Survey Satellite. We achieved a photometric precision in line with expectations from photon statistics, reaching 0.01 mag for 8 ≲ H ≲ 11 mag. We used the resulting Cepheid light curves to derive corrections to “mean light” for random-phase Hubble Space Telescope observations in F160W. We find good agreement with previous phase corrections based on VI light curves from the literature, with a mean difference of −1 ± 6 mmag.

Near-earth asteroid (66391) Moshup (1999 KW4) observing campaign: Results from a global planetary defense characterization exercise

Hazards due to near-Earth objects (NEOs) continue to pose a threat to life on Earth. While our capability for discovering NEOs has steadily progressed over the last three decades, physical characterization of a representative population has lagged behind. To test the operational readiness of the global planetary defense capabilities, we conducted a community-led global planetary defense exercise, with support from the NASA's Planetary Defense Coordination Office (PDCO) and the International Asteroid Warning Network (IAWN), to test the operational readiness of global planetary defense capabilities. This campaign focused on the characterization (direct imaging, radar, spectroscopy) of the binary near-Earth asteroid (NEA) (66391) Moshup (formerly known as 1999 KW4) and its moon Squannit. We chose a binary system because roughly one in six large NEAs are binaries. An additional goal was to apply lessons learned from this campaign towards ground-based characterization campaign for binary NEA (65803) Didymos, the target of the PDCO's Double Asteroid Redirection Test (DART) and the European Space Agency's Hera missions. Spectral observations of Moshup from the NASA Infrared Telescope Facility (IRTF) show similarities to Q-type asteroids. Based on its spectral band parameters, the best meteorite analogs for Moshup are L chondrites. We did not detect a hydration feature at 3 μm, which suggests that the entire surface is anhydrous. We imaged the binary using the SPHERE instrument on the Very Large Telescope (VLT) and obtained resolved spectral measurements of Moshup similar to those obtained with the NASA IRTF. Squannit appears to have slightly redder spectral slope than Moshup. Radar observations Arecibo Observatory at 2380 MHz indicate a polarization ratio of ~0.4, which is higher than the average values for the S complex asteroids, which includes Q types. The visible extent of the components from the radar observations, taken as proxies for their radii, suggest Moshup and Squannit have diameters of 1500 ± 120 m and 480 ± 60 m, respectively. We constrain the system mass to 2.2 ± 0.5 × 1012 kg with a maximum range for bulk density between ~0.8 g/cm3 for a very low-mass system with spherical shapes up to 2.7 g/cm3 for very high-mass system where Moshup has a more ridged-ball shape. We note that the radar-derived parameters presented in the paper are for the purposes of this exercise and do not supersede those in Ostro et al. (2006). We assessed the impact risk of a hypothetical impactor based on Moshup's physical properties using the Probabilistic Asteroid Impact Risk (PAIR) model. We assessed three impact risk scenarios at different epochs as the state of knowledge of Moshup improved. For kilometer-scale impactors like Moshup, the risk is driven predominantly by the potential for global climatic effects (95–97% of cases across the epochs) with a few percent driven by local damage and a few tenths of a percent driven by tsunami.

Volatile Composition and Outgassing in C/2018 Y1 (Iwamoto): Extending Limits for High-resolution Infrared Cometary Spectroscopy between 2.8 and 5.0 μm

Abstract We used the powerful high spectral resolution cross-dispersed facility spectrograph, iSHELL, at the NASA Infrared Telescope Facility (IRTF) to observe C/2018 Y1 (Iwamoto), a long-period comet from the Oort cloud. We report production rates for water and eight other parent molecules (native ices), C2H6, CO, CH4, H2CO, CH3OH, HCN, NH3, and C2H2, on three preperihelion UT dates, 2019 January 13 and (near perihelion) February 4–5. We present abundance ratios relative to both C2H6 (a nonpolar molecule) and H2O (a polar molecule), thereby providing a more complete picture of the parent volatile composition of C/2018 Y1 and potential associations of ices in its nucleus. Overall, the measured spatial distributions for polar molecules (in particular, H2O and CH3OH) were broader, exhibiting more complex structure compared with nonpolar or weakly polar species (CH4, C2H6, and CO). Our January 13 results permitted quantitatively assessing the significant improvement in sensitivity delivered by iSHELL compared with previous capabilities at the IRTF. The efficient spectral coverage of iSHELL plus the favorable geocentric Doppler shift of C/2018 Y1 allowed for measuring >50% of CH4 ν 3-band emission intensity on both January 13 and February 5. Compositionally, compared to their respective mean abundances among comets from the Oort cloud, C2H6 and CH3OH were enriched, CH4 and HCN were near normal, and all other species were depleted. The abundance ratio CH3OH/C2H6 was higher by 45% ± 8% on January 13 versus February 5, whereas CH4/C2H6 was unchanged within the uncertainty, suggesting nonhomogeneous composition among regions of the nucleus dominating activity on these dates.

Orion Bar as a window to the evolution of PAHs

ABSTRACT We investigate the mid-infrared (IR) emission in the Orion Bar photodissociation region (PDR), using archival photometric and spectroscopic observations from the United Kingdom Infrared Telescope (UKIRT), Spitzer, Infrared Space Observatory(ISO), and Stratospheric Observatory for Infrared Astronomy (SOFIA) telescopes. Specifically, we consider flux densities of the emission bands at 3.3, 3.4, 3.6, 6.6, 7.7, and 11.2 $\mu$m in several locations and a spectrum from 3 to 45 $\mu$m in one location. We study the behaviour of band flux ratios, which are sensitive to external conditions, as revealed by their variations with the distance from an ionizing source. Assuming that the mid-IR emission arises mostly from polycyclic aromatic hydrocarbons (PAHs), and that a weak emission feature at 3.4 $\mu$m is related to PAHs with extra hydrogen atoms (H-PAHs), we trace variations of the ratios using a model for PAH evolution. Namely, we estimate how populations of PAHs of different sizes, hydrogenation and ionization states change across the Orion Bar over a time interval approximately equal to its lifetime. The obtained ensembles of PAHs are further used to calculate the corresponding synthetic spectra and band flux densities. The model satisfactorily describes the main features of the ratios I3.6/I11.2, I7.7/I11.2, I7.7/I3.6, and I3.3/I3.4. We conclude that the best coincidence between modelling and observations is achieved if C loss of PAHs is limited by the number of carbon atoms NC = 60, and the band at 3.4 $\mu$m may indeed be attributed to H-PAHs. We confirm that large cations dominate at the surface of the PDR but small neutral PAHs and anions are abundant deeper in the molecular cloud.

Long Term Evolution of Surface Features on the Red Supergiant AZ Cyg

Abstract We present H-band interferometric observations of the red supergiant (RSG) AZ Cyg that were made with the Michigan Infra-Red Combiner (MIRC) at the six-telescope Center for High Angular Resolution Astronomy (CHARA) Array. The observations span 5 yr (2011–2016), which offers insight into the short and long-term evolution of surface features on RSGs. Using a spectrum of AZ Cyg obtained with SpeX on the NASA InfraRed Telescope Facility (IRTF) and synthetic spectra calculated from spherical MARCS, spherical PHOENIX, and SAtlas model atmospheres, we derive T eff is between 3972 K and 4000 K and log g between −0.50 and 0.00, depending on the stellar model used. Using fits to the squared visibility and GAIA parallaxes, we measure its average radius R = 911 − 50 + 57 R ⊙ . Reconstructions of the stellar surface using our model-independent imaging codes SQUEEZE and OITOOLS.jl show a complex surface with small bright features that appear to vary on a timescale of less than one year and larger features that persist for more than one year. The 1D power spectra of these images suggest a characteristic size of 0.52–0.69 R ⋆ for the larger, long lived features. This is close to the values of 0.51–0.53 R ⋆ that are derived from 3D RHD models of stellar surfaces. We conclude that interferometric imaging of this star is in line with predictions of 3D RHD models but that short-term imaging is needed to more stringently test predictions of convection in RSGs.

Chemical Composition of Outbursting Comet C/2015 ER61 (PanSTARRS)

Abstract Comet C/2015 ER61 (PanSTARRS) is a long-period Oort cloud comet whose favorable approach to the inner parts of the solar system in 2017 April–May enabled us to characterize its primary volatile composition using the iSHELL spectrograph mounted on the 3 m NASA Infrared Telescope Facility (IRTF) on Maunakea, Hawaii. We used three iSHELL settings (covering ∼2.8–5.2 μm) to sample fluorescent emissions from H 2 O, OH, CH 3 OH, HCN, C 2 H 2 , NH 3 , CO, CH 4 , C 2 H 6 , H 2 CO, and OCS on multiple dates ranging from UT 2017 April 15 (shortly after its April 4 outburst) to May 13, nearly 30 days before the detection of its double nucleus. Our observations also offered the opportunity to obtain sensitive 3 σ upper limits for cyanoacetylene ( HC 3 N). We report rotational temperatures ( T rot ), production rates (Qs), abundance (mixing) ratios (relative to H 2 O and C 2 H 6 ), and spatial distributions in the coma. ER61 exhibits variability in production rates of many species on short (day-to-day) and long (pre- versus post-perihelion) timescales. The relative abundances of these volatile species remained consistent within uncertainties during our pre-perihelion observations but tended to decrease during our post-perihelion observations (with the exception of CH 3 OH and HCN). The short-timescale variability in the production rates of these volatiles could be due to diurnal effects (over the course of the rotation of the nucleus) and/or the effect of its outburst. The decrease in the production rates and hence the mixing ratios in some volatiles in post-perihelion dates could be due to the presence of seasonal effects in ER61.