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The molecular gas in the central molecular zone (CMZ) of the Galaxy has been studied using infrared absorption spectra of H3+ lines at 3.5–4.0 μm and CO lines near 2.34 μm. In addition to the previously reported spectra of these lines toward eight stars located within 30 pc of Sgr A*, there are now spectra toward ∼30 bright stars located from 140 pc west to 120 pc east of Sgr A*. The spectra show the presence of warm (T ∼ 200 K) and diffuse (n < 100 cm−3) gas with N(H3+) ∼ 3 × 1015 cm−2 on the majority of sight lines. Instead of our previous analysis, in which only electrons from photoionization of carbon atoms were considered, we have developed a simple model calculation in which the cosmic-ray ionization of H2 and H is also taken into account. We conclude the following: (1) Warm and diffuse gas dominates the volume of the CMZ. The volume filling factor of dense gas must be much less than 0.1, and the CMZ is not as opaque as previously considered. The X-ray-emitting ultrahot 108 K plasma, which some thought to dominate the CMZ, does not exist over extended regions. (2) The cosmic-ray ionization rate is ζ ∼ 2 × 10−14 s−1, higher than in Galactic dense clouds and diffuse clouds by factors of ∼1000 and ∼100, respectively. If the equipartition law stands, this suggests a pervading magnetic field on the order of ∼100 μG. [ABSTRACT FROM AUTHOR]

Half of the energy emitted by late-T- and Y-type brown dwarfs emerges at 3.5 ≤ λμm ≤ 5.5. We present new L′ (3.43 ≤ λμm ≤ 4.11) photometry obtained at the Gemini North telescope for nine late-T and Y dwarfs, and synthesize L′ from spectra for an additional two dwarfs. The targets include two binary systems that were imaged at a resolution of 0.″25. One of these, WISEP J045853.90+643452.6AB, shows significant motion, and we present an astrometric analysis of the binary using Hubble Space Telescope, Keck Adaptive Optics, and Gemini images. We compare λ ∼ 4 μm observations to models, and find that the model fluxes are too low for brown dwarfs cooler than ∼700 K. The discrepancy increases with decreasing temperature, and is a factor of ∼2 at Teff = 500 K and ∼4 at Teff = 400 K. Warming the upper layers of a model atmosphere generates a spectrum closer to what is observed. The thermal structure of cool brown dwarf atmospheres above the radiative-convective boundary may not be adequately modeled using pure radiative equilibrium; instead heat may be introduced by thermochemical instabilities (previously suggested for the L- to T-type transition) or by breaking gravity waves (previously suggested for the solar system giant planets). One-dimensional models may not capture these atmospheres, which likely have both horizontal and vertical pressure/temperature variations. [ABSTRACT FROM AUTHOR]

We present high-resolution images of NGC 2071-IR in the J, H, and K bands and in the emission at 2.12 μm of the v = 1–0 S(1) line of molecular hydrogen. We also present moderate-resolution K-band spectra of two young stellar objects, IRS 1 and IRS 3, within NGC 2071-IR, that are candidate sources of one or more of the outflows observed in the region. Two of the eight originally identified infrared point sources in NGC 2071-IR are binaries, and we identify two new sources, one coincident with the radio source Very Large Array-1 and highly reddened. The H2Q(3)/S(1) line intensity ratios at IRS 1 and IRS 3 yield high and very high extinctions, respectively, to them, as is implied by their near-infrared colors and K-band continuum slopes. The spectra also reveal the presence of hot, dense circumstellar molecular gas in each, suggesting that both are strong candidates for having energetic molecular outflows. We agree with a previous suggestion that IRS 1 is the likely source of an east–west-oriented outflow and conclude that this outflow is probably largely out of the plane of the sky. We also conclude that if IRS 3 is the source of the large-scale northeast–southwest outflow, as has been previously suggested, its jet/wind must precess in order to explain the angular width of that outflow. We discuss the nature of the point sources and their possible contributions, if any, to the complex morphology of the H2 line emission. [ABSTRACT FROM AUTHOR]

We briefly describe the results of a K-band spectroscopic survey of over 500 highly reddened point-like objects on sightlines toward the Central Molecular Zone (CMZ) of the Galaxy. The goal was to find stars with featureless or nearly featureless spectra suitable for near- and mid-infrared absorption spectroscopy of the Galactic center’s interstellar gas on sightlines spread across the CMZ. Until recently only a few such stars have been known outside of very localized sightlines in the vicinity of the Quintuplet and Central clusters. We have used Spitzer Space Telescope Galactic Legacy Infrared Midplane Survey Extraordinaire and Two-Micron All-Sky Survey photometry to select promising candidates, and over the last 10 years have been acquiring low-resolution K-band spectra of them. As expected, the vast majority are cool and/or highly reddened red giants with complex photospheric spectra unsuitable for measuring faint interstellar lines. Approximately 10% of them, whose observations are reported here, have featureless or nearly featureless spectra. Although not evenly distributed in Galactic longitude, these stars are scattered across the CMZ. Many of them are luminous stars that are deeply embedded in warm dust cocoons, and have K-band continua rising steeply to longer wavelengths. A significant fraction of them are hot stars of a variety of spectral types, including at least five newly discovered Wolf–Rayet stars. All of them should be suitable for spectroscopy of interstellar absorption lines at infrared wavelengths greater than 3 μm and many are also suitable at shorter wavelengths. [ABSTRACT FROM AUTHOR]

We report the detection of a number of emission lines in the 1.0–2.4 μm spectra of four of the five bright-infrared dust-embedded stars at the center of the Galactic center’s (GC) Quintuplet Cluster. Spectroscopy of the central stars of these objects is hampered not only by the large interstellar extinction that obscures all of the objects in the GC, but also by the large amounts of warm circumstellar dust surrounding each of the five stars. The pinwheel morphologies of the dust observed previously around two of them are indicative of Wolf–Rayet colliding wind binaries; however, infrared spectra of each of the five have until now revealed only dust continua steeply rising to long wavelengths and absorption lines and bands from interstellar gas and dust. The emission lines detected, from ionized carbon and from helium, are broad and confirm that the objects are dusty late-type carbon Wolf–Rayet stars. [ABSTRACT FROM AUTHOR]

Vibration–rotation lines of H2 from highly excited levels approaching the dissociation limit have been detected at a number of locations in the shocked gas of the Orion Molecular Cloud (OMC-1), including in a Herbig–Haro object near the tip of one of the OMC-1 “fingers.” Population diagrams show that, while the excited H2 is almost entirely at a kinetic temperature of ∼1800 K (typical for vibrationally shock-excited H2), as in the previously reported case of Herbig–Haro object HH 7 up to a few percent of the H2 is at a kinetic temperature of ∼5000 K. The location with the largest fraction of hot H2 is the Herbig–Haro object, where the outflowing material is moving at a higher speed than at the other locations. Although theoretical work is required for a better understanding of the 5000 K H2 (including how it cools), its existence and the apparent dependence of its abundance relative to that of the cooler component on the relative velocities of the outflow and the surrounding ambient gas appear broadly consistent with it having recently reformed. The existence of this high-temperature H2 appears to be a common characteristic of shock-excited molecular gas. [ABSTRACT FROM AUTHOR]

We have obtained K-band spectra at R ∼ 5000 and an angular resolution of 0.″3 of a section of the Herbig–Haro 7 (HH7) bow shock, using the Near-Infrared Integral Field Spectrograph at Gemini North. Present in the portion of the data cube corresponding to the brightest part of the bow shock are emission lines of H2 with upper state energies ranging from ∼6000 K to the dissociation energy of H2, ∼50,000 K. Because of low signal-to-noise ratios, the highest excitation lines cannot be easily seen elsewhere in the observed region. However, excitation temperatures, measured throughout much of the observed region using lines from levels as high as 25,000 K, are a strong function of upper level energy, indicating that the very highest levels are populated throughout. The level populations in the brightest region are well fit by a two-temperature model, with 98.5% of the emitting gas at T = 1800 K and 1.5% at T = 5200 K. The bulk of the H2 line emission in HH7, from the 1800 K gas, has previously been well-modeled by a continuous shock, but the 5200 K cozmponent is inconsistent with standalone standard continuous shock models. We discuss various possible origins for the hot component and suggest that this component is H2 newly reformed on dust grains and then ejected from them, presumably following dissociation of some of the H2 by the shock. [ABSTRACT FROM AUTHOR]

Spectra of the archetypal Type II Seyfert galaxy NGC 1068 in a narrow wavelength interval near 3.7 μm have revealed a weak absorption feature due to two lines of the molecular ion The observed wavelength of the feature corresponds to a velocity of −70 km s−1 relative to the systemic velocity of the galaxy, implying an outward flow from the nucleus along the line of sight. The absorption by H along with the previously known broad hydrocarbon absorption at 3.4μm are probably formed in diffuse gas that is in close proximity to the continuum source, i.e., within a few tens of parsecs of the central engine. Based on that conclusion and the measured H absorption velocity and with the assumption of a spherically symmetric wind we estimate a rate of mass outflow from the active galactic nucleus of ∼1 M⊙ yr−1. [ABSTRACT FROM AUTHOR]

We report high-resolution near-infrared absorption spectroscopy of H2, H3+, and CO toward the young high mass object NGC 7538 IRS 1. The v = 1–0 H2S(0) line and lines in the CO v = 2–0 band were detected; the v = 1–0 H2S(1) line and the v = 1–0 H3+ lines [R(1, 1)l, R(1, 0), R(1, 1)u] were not detected. The line of sight traverses two clouds, with temperatures 45 and 259 K and with roughly equal column densities of CO. Assuming that H2 is at the same temperature as CO and that the two species are uniformly mixed, [H2]/[CO] = 3600 ± 1200. NGC 7538 is the most distant object from the Galactic center for which [H2]/[CO] has been directly measured using infrared absorption spectroscopy. [ABSTRACT FROM AUTHOR]

The luminous Class I protostar HBC 494, embedded in the Orion A cloud, is associated with a pair of reflection nebulae, Re50 and Re50N, which appeared sometime between 1955 and 1979. We have found that a dramatic brightening of Re50N has taken place sometime between 2006 and 2014. This could result if the embedded source is undergoing a FUor eruption. However, the near-infrared spectrum shows a featureless very red continuum, in contrast to the strong CO bandhead absorption displayed by FUors. Such heavy veiling, and the high luminosity of the protostar, is indicative of strong accretion but seemingly not in the manner of typical FUors. We favor the alternative explanation that the major brightening of Re50N and the simultaneous fading of Re50 is caused by curtains of obscuring material that cast patterns of illumination and shadows across the surface of the molecular cloud. This is likely occurring as an outflow cavity surrounding the embedded protostar breaks through to the surface of the molecular cloud. Several Herbig–Haro objects are found in the region. [ABSTRACT FROM AUTHOR]