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DK Cha is an intermediate-mass star in transition from an embedded configuration to a star plus disk stage. We aim to study the composition and energetics of the circumstellar material during this pivotal stage. Using the Range Scan mode of PACS on the Herschel Space Observatory, we obtained a spectrum of DK Cha from 55 to 210 micron as part of the DIGIT Key Program. Almost 50 molecular and atomic lines were detected, many more than the 7 lines detected in ISO-LWS. Nearly the entire ladder of CO from J=14-13 to 38-37 (E_u/k = 4080 K), water from levels as excited as E_u/k = 843 K, and OH lines up to E_u/k = 290 K were detected. The continuum emission in our PACS SED scan matches the flux expected from a model consisting of a star, a surrounding disk of 0.03 Solar mass, and an envelope of a similar mass, supporting the suggestion that the object is emerging from its main accretion stage. Molecular, atomic, and ionic emission lines in the far-infrared reveal the outflow's influence on the envelope. The inferred hot gas can be photon-heated, but some emission could be due to C-shocks in the walls of the outflow cavity., Comment: 4 Page letter, To appear in A&A special issue on Herschel

In this paper we present high resolution 4.7micron spectra of the isolated Herbig Be star HD100546. HD100546 has been the subject of intense scrutiny because it is a young nearby star with a transitional disk. We observe the Delta v=1 ro-vibrational CO transitions in order to clarify the distribution of warm gas in the inner disk. Modeling of the CO spectrum indicates that the gas is vibrationally excited by collisions and UV fluorescence. The observed emission extends from 13-100AU. The inner edge of the molecular gas emission is consistent with the inner edge of the optically thick dust disk indicating that the inner hole is not simply a hole in the dust opacity but is likely cleared of gas as well. The rotational temperature of the CO is ~1000K - much hotter than the ~200K CO in the otherwise similar transitional disk surrounding HD141569. The origin of this discrepancy is likely linked to the brighter PAH emission observed toward HD100546. We use the excitation of the CO to constrain the geometry of the inner disk and comment on the evolutionary state of the system., Comment: 26 pages, 15 figures, Accepted by ApJ

We present spectra of a sample of Herbig Ae and Be (HAeBe) stars obtained with the Infrared Spectrograph on the Spitzer Space Telescope. All but one of the Herbig stars show emission from polycyclic aromatic hydrocarbons (PAHs) and seven of the spectra show PAH emission, but no silicate emission at 10 microns. The central wavelengths of the 6.2, 7.7--8.2, and 11.3 micron emission features decrease with stellar temperature, indicating that the PAHs are less photo-processed in cooler radiation fields. The apparent low level of photo processing in HAeBe stars, relative to other PAH emission sources, implies that the PAHs are newly exposed to the UV-optical radiation fields from their host stars. HAeBe stars show a variety of PAH emission intensities and ionization fractions, but a narrow range of PAH spectral classifications based on positions of major PAH feature centers. This may indicate that, regardless of their locations relative to the stars, the PAH molecules are altered by the same physical processes in the proto-planetary disks of intermediate-mass stars. Analysis of the mid-IR spectral energy distributions indicates that our sample likely includes both radially flared and more flattened/settled disk systems, but we do not see the expected correlation of overall PAH emission with disk geometry. We suggest that the strength of PAH emission from HAeBe stars may depend not only on the degree of radial flaring, but also on the abundance of PAHs in illuminated regions of the disks and possibly on the vertical structure of the inner disk as well., 52 pages, 12 figures

We present a discussion of the science drivers and design approach for a high-resolution, mid-infrared spectrograph for the Thirty-Meter Telescope. The instrument will be integrated with an adaptive optics system optimized for the midinfrared; as a consequence it is not significantly larger or more complex than similar instruments designed for use on smaller telescopes. The high spatial and spectral resolution possible with such a design provides a unique scientific capability. The design provides spectral resolution of up to 120,000 for the 4.5-25 �� m region in a cross-dispersed format that provides continuous spectral coverage of up to 2% to 14 �� m. The basic concept is derived from the successful TEXES mid-infrared spectrograph. To facilitate operation, there are separate imaging channels for the near-infrared and the mid-infrared; both can be used for acquisition and the mid-infrared imaging mode can be used for science imaging and for guiding. Because the spectrograph is matched to the diffraction limit of a 30-m telescope, gains in sensitivity are roughly proportional to the square of the telescope diameter, opening up a volume within the Galaxy a thousand times greater than existing instruments.

We present the first Spitzer Infrared Spectrograph (IRS; The IRS was a collaborative venture between Cornell University and Ball Aerospace Corporation funded by NASA through the Jet Propulsion Laboratory and the Ames Research Center.) observations of the disks around classical T Tauri stars: spectra in the 5.2-30 micron range of six stars. The spectra are dominated by emission features from amorphous silicate dust, and a continuous component from 5 to 8 microns that in most cases comprises an excess above the photosphere throughout our spectral range. There is considerable variation in the silicate feature/continuum ratio, which implies variations of inclination, disk flaring, and stellar mass accretion rate. In most of our stars, structure in the silicate feature suggests the presence of a crystalline component. In one, CoKu Tau/4, no excess above the photosphere appears at wavelengths shortward of the silicate features, similar to 10 Myr old TW Hya, Hen 3-600, and HR 4796A. This indicates the optically thick inner disk is largely absent. The silicate emission features with peaks at 9.7 and 18 microns indicate small dust grains are present. The extremely low 10-20 micron color temperature of the dust excess, 135 K, indicates these grains are located more than 10 AU from the star. These features are suggestive of gravitational influence by planets or close stellar companions and grain growth in the region within 10 AU of the star, somewhat surprising for a star this young (1 Myr)., Comment: AASTEX, 10 pages text, 2 figures, 1 table, published September 2004 in The Astrophysical Journal Supplement Series

We report spectra obtained with the Spitzer Space Telescope in the 5 to 35 micron range of HD 233517, an evolved K2 III giant with circumstellar dust. At wavelengths longer than 13 microns, the flux is a smooth continuum that varies approximately as frequency to the -5/3 power. For wavelengths shorter than 13 microns, although the star is oxygen-rich, PAH features produced by carbon-rich species at 6.3 microns, 8.2 microns, 11.3 microns and 12.7 microns are detected along with likely broad silicate emission near 20 microns. These results can be explained if there is a passive, flared disk orbiting HD 233517. Our data support the hypothesis that organic molecules in orbiting disks may be synthesized in situ as well as being incorporated from the interstellar medium., Comment: 11 pages, 2 figures, ApJ Letters, in press

We utilized the new high-order (250-378 mode) Magellan Adaptive Optics system (MagAO) to obtain very high-resolution science in the visible with MagAO's VisAO CCD camera. In the good-median seeing conditions of Magellan (0.5–0.7″) we find MagAO delivers individual short exposure images as good as 19 mas optical resolution. Due to telescope vibrations, long exposure (60s) r' (0.63μm) images are slightly coarser at FWHM = 23-29 mas (Strehl ~ 28%) with bright (R < 9 mag) guide stars. These are the highest resolution filled-aperture images published to date. Images of the young (~ 1 Myr) Orion Trapezium θ1 Ori A, B, and C cluster members were obtained with VisAO. In particular, the 32 mas binary θ1 Ori C1C2 was easily resolved in non-interferometric images for the first time. Relative positions of the bright trapezium binary stars were measured with ~ 0.6–5 mas accuracy. In the second commissioning run we were able to correct 378 modes and achieved good contrasts (Strehl>20% on young transition disks at Hα). We discuss the contrasts achieved at Hα and the possibility of detecting low mass (~ 1–5 Mjup) planets (past 5AU) with our new SAPPHIRES survey with MagAO at Hα.

We report spectra obtained with the Spitzer Space Telescope in the wavelength range between 14 microns and 35 microns of 19 nearby main-sequence stars with infrared excesses. The six stars with strong dust emission show no recognizable spectral features, suggesting that the bulk of the emitting particles have diameters larger than 10 microns. If the observed dust results from collisional grinding of larger solids, we infer minimum masses of the parent body population between 0.004 of the Earth's mass and 0.06 of the Earth's mass. We estimate grain production rates of 10 Gg/s around lambda Boo and HR 1570; selective accretion of this matter may help explain their peculiar surface abundances. There appear to be inner truncations in the dust clouds at 48 AU, 11 AU, 52 AU and 54 AU around HR 333, HR 506, HR 1082 and HR 3927, respectively., 11 pages, 1 figure, ApJ Supplement, Spitzer special issue, in press

We present Keck LWS images of the Orion BN/KL star forming region obtained in the first multi-wavelength study to have 0.3-0.5" resolution from 4.7 to 22 microns. The young stellar objects designated infrared source-n and radio source-I are believed to dominate the BN/KL region. We have detected extended emission from a probable accretion disk around source-n but infer a stellar luminosity on the order of only 2000 Lsun. Although source-I is believed to be more luminous, we do not detect an infrared counterpart even at the longest wavelengths. However, we resolve the closeby infrared source, IRc2, into an arc of knots ~1000 AU long at all wavelengths. Although the physical relation of source-I to IRc2 remains ambiguous, we suggest these sources mark a high density core (10^7-10^8 pc^-3 over 1000 AU) within the larger BN/KL star forming cluster. The high density may be a consequence of the core being young and heavily embedded. We suggest the energetics of the BN/KL region may be dominated by this cluster core rather than one or two individual sources., Comment: 13 pages including 3 color figures. Accepted to The Astrophysical Journal Letters pending slight reduction in length. High resolution figures (jpeg) may be found at http://cfa-www.harvard.edu/~lincoln/keck.bnkl.midir.ppr/

We describe some of the science programs that drive the need for the next generation ground-based OIR telescope. The programs are chosen to illustrate the power of such a telescope to enable new kinds of science via combinations of sensitivity, field-of-view, wavelength coverage, and spectral resolution.

We analyze the OH rotational emission in the Spitzer Space Telescope mid-infrared spectrum of the T Tauri star DG Tau. OH is observed in emission from upper level energies of 1900 K to 28,000 K. The rotational diagram cannot be fit with any single combination of temperature and column density and has slopes that correspond to excitation temperatures ranging from 200 K to 6000 K. The relative Λ-doublet population within each rotational level is not equal, showing that the OH population is not in thermal equilibrium. The symmetric Λ-doublet state is preferred in all rotational states, with an average of 0.5 for the population ratio of the anti-symmetric to symmetric state. We show that the population distribution of the high rotational lines and the Λ-doublet ratio are consistent with the formation of OH following the photo-dissociation of H{sub 2}O by FUV photons in the second absorption band of water (∼1150-1400 A), which includes Lyα. Other processes, OH formation from either photo-dissociation of water in the first absorption band (1450-1900 A) or the reaction O({sup 1} D) + H{sub 2}, or collisional excitation, cannot explain the observed emission in the high rotational states but could potentially contribute to the population ofmore » lower rotational levels. These results demonstrate that the photodissociation of water is active in DG Tau and support the idea that the hot rotational OH emission commonly observed in Classical T Tauri stars is due to the dissociation of H{sub 2}O by FUV radiation.« less

We present the discovery of CO fundamental ro-vibrational emission from the classical T Tauri spectroscopic binary DQ Tau. The high-resolution infrared echelle spectra reveal emission lines from both the v=1 and v=2 vibrational levels with line widths of roughly 70 km/s. The average CO excitation temperature is approximately 1200 K. We model the spectra as arising from gas in Keplerian rotation about the center-of-mass of the binary. The disk model requires gas with an average surface density of 5 x 10-4 g cm-2 that extends outward to 0.5 +/- 0.1 AU and inward to at least 0.1 AU from the center-of-mass. The radial extent for the emitting gas is close to the predicted size of the gap in the DQ Tau accretion disk that is expected to be dynamically cleared by the binary. We interpret these results, and previous modeling of DQ Tau's spectral energy distribution, as evidence for a small amount (~ 1e-10 Msun) of diffuse material residing within the optically-thin disk gap. Thus dynamical clearing has not been completely efficient in the DQ Tau binary. We suggest that the material is associated with a flow from the circumbinary disk which feeds the ongoing accretion at the stellar surfaces., Comment: to be published in The Astrophysical Journal

We present the first near-IR spectroscopy of the z=1.5 radio-loud BALQSO FIRST J155633.8+351758. Both the Balmer decrement and the slope of the rest-frame UV-optical continuum independently suggest a modest amount of extinction along the line of sight to the BLR (E(B-V)~0.5 for SMC-type screen extinction at the QSO redshift). The implied gas column density along the line of sight is much less than is implied by the weak X-ray flux of the object, suggesting that either the BLR and BAL region have a low dust-to-gas ratio, or that the rest-frame optical light encounters significantly lower mean column density lines of sight than the X-ray emission. From the rest-frame UV-optical spectrum, we are able to constrain the stellar mass content of the system. Comparing the maximal stellar mass with the black hole mass estimated from the bolometric luminosity of the QSO, we find that the ratio of the black hole to stellar mass may be comparable to the Magorrian value, which would imply that the Magorrian relation is already in place at z=1.5. However, multiple factors favor a much larger black hole to stellar mass ratio. This would imply that if the Magorrian relation characterizes the late history of QSOs, and the situation observed for F1556+3517 is typical of the early evolutionary history of QSOs, central black hole masses develop more rapidly than bulge masses. [ABRIDGED], Comment: 23 pages, 4 embedded postscript figures; Accepted for publication in The Astronomical Journal, December 2000

The discovery of extra-solar planets has captured the imagination and interest of the public and scientific communities alike, and for the same reasons: we are all want to know the answers to questions such as “Where do we come from?” and “Are we alone?” Throughout this century, popular culture has presumed the existence of other worlds and extra-terrestrial intelligence. As a result, the annals of popular culture are filled with thoughts on what extra-solar planets and their inhabitants are like. And now toward the end of the century, astronomers have managed to confirm at least one aspect of this speculative search for understanding in finding convincing evidence of planets beyond the solar system.

High resolution spectroscopy experiments with visible adaptive optics (AO) telescopes at Starfire Optical Range and Mt. Wilson have demonstrated that spectral resolution can be routinely improved by a factor of - 10 over the seeing-limited case with no extra light losses at visible wavelengths. With large CCDs now available, a very wide wavelength range can be covered in a single exposure. In the near future, most large ground-based telescopes will be equipped with powerful A0 systems. Most of these systems are aimed primarily at diffraction-limited operation in the near IR. An exciting new opportunity will thus open up for high resolution IR spectroscopy. Immersion echelle gratings with much coarser grooves being developed by us at LLNL will play a critical role in achieving high spectral resolution with a compact and low cost IR cryogenically cooled spectrograph and simultaneous large wavelength coverage on relatively small IR detectors. We have constructed a new A0 optimized spectrograph at Steward Observatory to provide R = 200,000 in the optical, which is being commissioned at the Starfire Optical Range 3.5m telescope. We have completed the optical design of the LLNL IR Immersion Spectrograph (LISPEC) to take advantage of improved silicon etching technology. Key words: adaptive optics, spectroscopy, high resolution, immersion gratings

We consider the asymptotic behavior of magnetocentrifugally driven X-winds, taking into proper account the pressure balance across the interface between the open stellar field lines of the dead zone devoid of matter and the open field lines of the wind. At large distances from the source the outflow collimates into jets along the rotation axis. Being almost cylindrically symmetric even close to the source of the outflow, the density distribution appears more jetlike than the collection of streamlines, which always contains a few members that skim over the surface of the disk.

We report high spectral resolution observations of the CO vibrational overtone emission from the young stellar object 1548C27; our observations include both the CO(2-0) and CO(5-3) bandhead regions. These data and similar observations of the young stellar object WL16, reported in a previous contribution to this journal, provide some of the most compelling evidence to date for the existence of inner disks around young stars. We describe the simple procedure that we use to synthesize bandhead emission from disks including the effect of thermal dissociation of CO and non-LTE excitation of the vibrational levels. Using this spectral synthesis procedure to extract the kinematics and physical properties of the emitting gas from the overtone data, we show how these high signal-to-noise data are also powerful probes of the stellar and inner disk properties of these systems. Our modeling is consistent with the identification of WL16 and 1548C27 as Herbig AeBe stars with stellar masses of approximately 2 and 4 solar masses, respectively. Thus, the kinematic signature of rotating disks in the overtone spectra of these sources provides strong support for the role of accretion disks in the formation of intermediate mass stars. For both WL16 and 1548C27, we interpret our modeling results as indicating that the overtone emission arises from a temperature inversion region in the inner disk atmosphere. We also find evidence for suprathermally broadened lines and are able to place useful constraints on the radial temperature and column density distributions of the CO line-formation region of the disk atmosphere., 38 pages (including figures) in gzip-ed uuencoded compressed postscript format. Accepted for publication in ApJ

Accretion disks are considered to be central to the formation of stars and planetary systems. While the evidence for disks around young stars is compelling, it is largely indirect, and most disk properties are inferred by modeling broadband spectral energy distributions. It is clearly important to establish kinematic evidence for disks and to identify useful spectroscopic measures of their physical properties. Towards such goals, we have been using high-resolution infrared spectroscopy to study the circumstellar environment of young stellar objects (YSOs). Results of our study of the CO overtone emission in several young stars are presented.

We present an analysis of Spitzer Infrared Spectrograph observations of H_(2)O, OH, HCN, C_(2)H_2, and CO_2 emission, and Keck-NIRSPEC observations of CO emission, from a diverse sample of T Tauri and Herbig Ae/Be circumstellar disks. We find that detections and strengths of most mid-IR molecular emission features are correlated with each other, suggesting a common origin and similar excitation conditions for this mid-infrared line forest. Aside from the remarkable differences in molecular line strengths between T Tauri, Herbig Ae/Be, and transitional disks discussed in Pontoppidan et al., we note that the line detection efficiency is anti-correlated with the 13/30 μm spectral slope, which is a measure of the degree of grain settling in the disk atmosphere. We also note a correlation between detection efficiency and Hα equivalent width, and tentatively with accretion rate, suggesting that accretional heating contributes to line excitation. If detected, H_(2)O line fluxes are correlated with the mid-IR continuum flux, and other co-varying system parameters, such as L_*. However, significant sample variation, especially in molecular line ratios, remains, and its origin has yet to be explained. Local thermal equilibrium (LTE) models of the H_(2)O emission show that line strength is primarily related to the best-fit emitting area, and this accounts for most source-to-source variation in H_(2)O emitted flux. Best-fit temperatures and column densities cover only a small range of parameter space, near ~10^(18) cm^(–2) and 450 K for all sources, suggesting a high abundance of H_(2)O in many planet-forming regions. Other molecules have a range of excitation temperatures from ~500 to 1500 K, also consistent with an origin in planet-forming regions. We find molecular ratios relative to water of ~10^(–3) for all molecules, with the exception of CO, for which n(CO)/n(H_(2)O) ~ 1. However, LTE fitting caveats and differences in the way thermo-chemical modeling results are reported make comparisons with such models difficult, and highlight the need for additional observations coupled with the use of line-generating radiative transfer codes.

We formulate the dynamical problem of a cool wind centrifugally driven from the magnetic interface of a young star and an adjoining Keplerian disk. We examine the situation for mildly accreting T Tauri stars that rotate slowly as well as rapidly accreting protostars that rotate near break-up. In both cases a wind can be driven from a small X-region just outside the stellar magnetopause, where the field lines assume an open geometry and are rooted to material that rotates at an angular speed equal both to the local Keplerian value and to the stellar angular speed. Assuming axial symmetry for the ideal magnetohydrodynamic flow, which requires us to postpone asking how the (lightly ionized) gas is loaded onto field lines, we can formally integrate all the governing equations analytically except for a partial equation that describes how streamlines spread in the meridional plane. Apart from the difficulty of dealing with PDEs of mixed type, finding the functional forms of the conserved quantities along streamlines - the ratio beta of magnetic field to mass flux, the specific energy H of the fluid in the rotating frame, and the total specific angular momentum J carried in the matter and the field - constitutes a standard difficulty in this kind of (Grad-Shafranov) formalism. Fortunately, because the ratio of the thermal speed of the mass-loss regions to the Keplerian speed of rotation of the interface constitutes a small parameter epsilon, we can attack the overall problem by the method of matched asymptotic expansions. This procedure leads to a natural and systematic technique for obtaining the relevant functional dependences of beta, H, and J. Moreover, we are able to solve analytically for the properties of the flow emergent from the small transsonic region driven by gas pressure without having to specify the detailed form of any of the conserved functions, beta, H, and J. This analytical solution provides inner boundary conditions for the numerical computation in a companion paper by Najita & Shu of the larger region where the main acceleration to terminal speeds occurs.

We construct steady, axisymmetric, numerical models of the sub-Alfvenic regions of cool winds driven by the X-celerator mechanism. We find that smooth acceleration to speeds of the order of the escape speed accompanied by substantial collimation of the flow can be achieved within the Alfven surface, located characteristically at several stellar radii. We apply the nondimensional results to winds which emerge from the equator of magnetized YSOs rotating at breakup and from circumstellar disks interacting with the magnetospheres of slowly rotating T Tauri stars. Stellar magnetic fields of kilogauss strength can drive wind mass-loss rates of 10(exp -6) solar mass/year from rapidly accreting YSOs and 10(exp -8) solar mass/year from slowly accreting T Tauri stars. The X-celerator mechanism can accelerate winds from these systems to velocities of hundreds of km/sec within a few stellar radii in the case of embedded YSOs and approximately 10 stellar radii in the case of T Tauri stars.

The effect of an evolving luminosity function (LF) on the ability of foreground galaxies to obscure background sources is discussed, using the Press-Schechter/CDM standard evolving LF model. Galaxies are modeled as simplified versions of local spirals and Poisson statistics are used to estimate the fraction of sky covered by intervening dusty galaxies and the mean optical depths due to these galaxies. The results are compared to those obtained in the case of nonevolving luminosity function in a low-density universe. It is found that evolution of the galaxy LF does not allow the quasar dust obscuration hypothesis to be sustained for dust disks with plausible sizes. Even in a low-density universe, where evolution at z = less than 10 is unimportant, large disk radii are needed to achieve the desired obscuring effect. The mean fraction of sky covered is presented as a function of the redshift z along with adequate diagram illustrations.

It is proposed that bipolar outflows from young stellar objects originate from a protostar rotating at breakup at its equator because it is being spun up by an adjoining accretion disk. Mass outflow at an appreciable fraction of the infall rate from a surrounding molecular cloud core onto the star and disk can be driven centrifugally if the protostar has a sufficiently strong magnetic field. The expansion of the flow toward the rotational poles may provide a collimation mechanism for focusing an ordinary stellar wind into optical jets.

We investigate how the detectability of signatures of self-gravity in a protoplanetary disc depends on its temporal evolution. We run a one-dimensional model for secular timescales to follow the disc mass as a function of time. We then combine this with three-dimensional global hydrodynamics simulations that employ a hybrid radiative transfer method to approximate realistic heating and cooling. We simulate ALMA continuum observations of these systems, and find that structures induced by the gravitational instability (GI) are readily detectable when $q=M_\mathrm{disc}/M_*\gtrsim 0.25$ and $R_\mathrm{outer}\lesssim 100$ au. The high accretion rate generated by gravito-turbulence in such a massive disc drains its mass to below the detection threshold in $\sim10^4$ years, or approximately 1 % of the typical disc lifetime. Therefore, discs with spiral arms detected in ALMA dust observations, if generated by self-gravity, must either be still receiving infall to maintain a high $q$ value, or have just emerged from their natal envelope. Detection of substructure in systems with lower $q$ is possible, but would require a specialist integration with the most extended configuration over several days. This disfavours the possibility of GI-caused spiral structure in systems with $q, 13 pages, 6 figures