We have observed 150 regions of massive star formation, selected originally by the presence of an H 2 O maser, in the J = 5→4, 3→2, and 2→1 transitions of CS, and 49 regions in the same transitions of C 34 S. Over 90% of the 150 regions were detected in the J = 2→1 and 3→2 transitions of CS and 75% were detected in the J=5→4 transition. We have combined the data with the J = 7→6 data from our original survey (Plume et al. 1992) to determine the density by analyzing the excitation of the rotational levels. Using Large Velocity Gradient (LVG) models, we have determined densities and column densities for 71 of these regions. The gas densities are very high ( log(n) = 5.9), but much less than the critical density of the J=7→6 line. Small maps of 25 of the sources in the J = 5→4 line yield a mean diameter of 1.0 pc. Several estimates of the mass of dense gas were made for the sources for which we had sufficient information. The mean virial mass is 3800 M ⊙ . The mean ratio of bolometric luminosity to virial mass (L/M ) is 190, about 50 times higher than estimates using CO emission, suggesting that star formation is much more efficient in the dense gas probed in this study. The gas depletion time for the dense gas is roughly 1.3 × 10 7 yr, comparable to the timescale for gas dispersal around open clusters and OB associations. We find no statistically significant linewidth-size or density-size relationships in our data. Instead, both linewidth and density are larger for a given size than would be predicted by the usual relationships. We find that the linewidth increases with density, the opposite of what would be predicted by the usual arguments. We estimate that the luminosity of our Galaxy (excluding the inner 400 pc) in the CS J = 5→4 transition is 15 to 23 L ⊙ , considerably less than the luminosity in this line within the central 100 pc of NGC 253 and M82. In addition, the ratio of far-infrared luminosity to CS luminosity is higher in M82 than in any cloud in our sample. Table 2 CS Source List CS J = 2-1 CS J = 3-2 CS J = 5-4 Source Flag T R * ∫T R * dV V LSR FWHM T R * ∫T R * dV V LSR FWHM T R * ∫T R * dV V LSR FWHM Name K K km s -1 km s -1 km s -1 K K km s -1 km s -1 km s -1 K K km s -1 km s -1 km s -1Table 2 CS Source List (Continued)4 Flag CS J = 2-1 CS J = 3-2 CS J = 5-4 Source T R * ∫T R * dV V LSR FWHM T R * ∫T R * dV V LSR FWHM T R * ∫T R * dV V LSR FWHM Name K K km s -1 km s -1 km s -1 K K km s -1 km s -1 km s -1 K K km s -1 km s -1 km s -1Table 2 CS Source List (Continued)6 CS J = 2-1 CS J = 3-2 CS J = 5-4 Source Flag T R * ∫T R * dV V LSR FWHM T R * ∫T R * dV V LSR FWHM T R * ∫T R * dV V LSR FWHM Name K K km s -1 km s -1 km s -1 K K km s -1 km s -1 km s -1 K K km s -1 km s -1 km s -1

We have mapped 63 regions forming high-mass stars in CS J ¼ 5 ! 4 using the CSO. The CS peak position was observed in C 34 S J ¼ 5 ! 4 toward 57 cores and in 13 CS J ¼ 5 ! 4 toward the nine brightest cores. The sample is a subset of a sample originally selected toward water masers; the selection on maser sources should favor sources in an early stage of evolution. The cores are located in the first and second Galactic quadrants with an average distance of 5:3 AE 3:7 kpc and were well detected with a median peak signalto-noise ratio in the integrated intensity of 40. The integrated intensity of CS J ¼ 5 ! 4 correlates very well with the dust continuum emission at 350 lm. For 57 sufficiently isolated cores, a well-defined angular size (FWHM) was determined. The core radius (R CS ), aspect ratio [ða=bÞ obs ], virial mass (M vir ), surface density (AE), and the luminosity in the CS J ¼ 5 ! 4 line (LðCS54Þ) are calculated. The distributions of size, virial mass, surface density, and luminosity are all peaked with a few cores skewed toward much larger values than the mean. The median values, l 1/2 , are as follows: l 1/2 ðR CS Þ ¼ 0:32 pc, l 1/2 ðða=bÞ obs Þ ¼ 1:20, l 1/2 ðM vir Þ ¼ 920 M , l 1/2 ðAEÞ ¼ 0:60 g cm À2 , l 1/2 ðLðCS54ÞÞ ¼ 1:9 Â 10 À2 L , and l 1/2 ðL bol =M vir Þ ¼ 165 ðL=MÞ . We find a weak correlation between C 34 S line width and size, consistent with Dv $ R 0:3 . The line widths are much higher than would be predicted by the usual relations between line width and size determined from regions of lower mass. These regions are very turbulent. The derived virial mass agrees within a factor of 2-3 with mass estimates from dust emission at 350 lm after corrections for the density structure are accounted for. The resulting cumulative mass spectrum of cores above 1000 M can be approximated by a power law with a slope of about À0.9, steeper than that of clouds measured with tracers of lower density gas and close to that for the total masses of stars in OB associations. The median turbulent pressures are comparable to those in UCH ii regions, and the pressures at small radii are similar to those in hypercompact H ii regions (P=k $ 10 10 K cm À3 ). The filling factors for dense gas are substantial, and the median abundance of CS is about 10 À9 . The ratio of bolometric luminosity to virial mass is much higher than the value found for molecular clouds as a whole, and the correlation of luminosity with mass is tighter.

We present near-infrared (1.0-2.4 µm) spectra confirming the youth and cool effective temperatures of 6 brown dwarfs and low mass stars with circumstellar disks toward the Chamaeleon II and Ophiuchus star forming regions. The spectrum of one of our objects indicates that it has a spectral type of ∼L1, making it one of the latest spectral type young brown dwarfs identified to date. Comparing spectra of young brown dwarfs, field dwarfs, and giant stars, we define a 1.49-1.56 µm H 2 O index capable of determining spectral type to ±1 sub-type, independent of gravity. We have also defined an index based on the 1.14 µm sodium feature that is sensitive to gravity, but only weakly dependent on spectral type for field dwarfs. Our 1.14 µm Na index can be used to distinguish young cluster members (τ 5 Myr) from young field dwarfs, both of which may have the triangular H-band continuum shape which persists for at least tens of Myr. Using T ef f 's determined from the spectral types of our objects along with luminosities derived from near and mid-infrared photometry, we place our objects on the H-R diagram and overlay evolutionary models to estimate the masses and ages of our young sources. Three of our sources have inferred ages (τ ≃10-30 Myr) significantly older than the median stellar age of their parent clouds (1-3 Myr). For these three objects, we derive masses ∼3 times greater than expected for 1-3 Myr old brown dwarfs with the bolometric luminosities of our sources. The large discrepancies in the inferred masses and ages determined using two separate, yet reasonable methods, emphasize the need for caution when deriving or exploiting brown dwarf mass and age estimates.

No abstract

We discuss the design and performance of TEXES, the Texas Echelon Cross Echelle Spectrograph. TEXES is a mid-infrared (5-25 µm) spectrograph with several operating modes: high-resolution, cross-dispersed with a resolving power of R = λ/δλ ≈ 100,000, 0.5% spectral coverage, and a ∼ 1.5 × 8 ′′ slit; medium-resolution long-slit, with R ≈ 15,000, 0.5% coverage, and a ∼ 1.5×45 ′′ slit; low-resolution long-slit, with δλ ≈ .004 µm, 0.25 µm coverage, and a ∼ 1.5 × 45 ′′ slit; and source acquisition imaging with 0.33 ′′ pixels and a 25 × 25 ′′ field of view on a 3 m telescope. TEXES has been used at the McDonald Observatory 2.7m and the IRTF 3m telescopes, and has proven to be both sensitive and versatile.Subject headings: infrared: general -instrumentation: spectrographs -techniques: spectroscopic Observatory (ISO) short wavelength spectrometer with R = λ/δλ ≈ 2000. SIRTF, with R ≈ 600 and much better sensitivity than can be achieved from the ground, will continue this study. However, neither of these spacecraft spectrometers was optimized for studies of narrow gas-phase lines.Mid-infrared ionic lines have been studied in a number of sources by several ground-based instruments, as well as by ISO. These lines provide information similar to that obtained from visible wavelength forbidden and recombination lines, but can be studied in much more obscured sources. With widths ≈ 10 − 100 km s −1 (the latter in external galaxies), these lines are best studied by instruments with R ∼ 10 4 . Our previous instrument, Irshell (Lacy et al. 1989), was optimized for the study of these lines. ISO greatly expanded on the earlier ground-based work, as will SIRTF, although the lower resolution on the space-based mid-IR spectrometers is insufficient for detailed kinematic studies.Less work has been done on molecular lines in the mid-infrared. In molecular clouds these lines have widths of only a few km s −1 , requiring R ≥ 100,000 for optimal sensitivity and to obtain kinematic information in line profiles. Although a few instruments have achieved such high resolution in the mid-infrared (heterodyne spectrometers, e.g. Mumma et al. 1982, and Fourier transform spectrometers, e.g. Ridgway & Brault 1984), the sensitivity of these instruments was sufficient for the study of only a few of the brightest objects in the sky. Considerable work has been done with ISO (e.g. Lahuis & van Dishoeck 2000) concentrating on the many lines of molecular Q-branches. Using Irshell, with R ≈ 10,000, we observed interstellar C 2 H 2 and CH 4 , as well as several other molecules, but could not resolve the individual lines except in regions of shocks or rapid outflows. As a result, we were limited to measurements of equivalent widths of often saturated lines. From this experience we concluded that whereas space-based spectrometers will improve on our observations of solid-state and ionic lines, at least in cases where high spatial resolution is not required, a high spectral resolution and high sensitivity ground-based (or airborne) spectrograph was required to fur...

Studying the properties of young planetary systems can shed light on how the dynamics and structure of planets evolve during their most formative years. Recent K2 observations of nearby young clusters (10-800 Myr) havefacilitated the discovery of such planetary systems. Here we report the discovery of a Neptune-sized planet transiting an M4.5 dwarf (K2-25) in the Hyades cluster (650-800 Myr). The lightcurve shows a strong periodic signal at 1.88 days, which we attribute to spot coverage and rotation. We confirm thatthe planet host is a member of the Hyades by measuring the radial velocity of the system with the high-resolution near-infrared spectrograph Immersion Grating Infrared Spectrometer. This enables us to calculate a distance based on K2-25ʼs kinematics and membership to the Hyades, which in turn provides a stellar radius and mass to ;5%-10%, better than what is currently possible for most Kepler M dwarfs (12%-20%). We use the derived stellar density as a prior on fitting the K2 transit photometry, which provides weak constraints on eccentricity. Utilizing a combination of adaptive optics imaging and high-resolution spectra, we rule out the possibility that the signal is due to a bound or background eclipsing binary, confirming the transits' planetary origin. K2-25b has a radius (3.43 0.31 0.95 -+ R ⊕ ) much larger than older Kepler planets with similar orbital periods (3.485 days) and host-star masses (0.29 M e ). This suggests that close-in planets lose some of their atmospheres past the first few hundred million years. Additional transiting planets around the Hyades, Pleiades, and Praesepe clusters from K2 will help confirm whether this planet is atypical or representative of other close-in planets of similar age.

We have combined new I, J, H, and Ks imaging of portions of the Chamaeleon II, Lupus I, and Ophiuchus star-forming clouds with with 3.6 to 24 µm imaging from the Spitzer Legacy Program, "From Molecular Cores to Planet Forming Disks", to identify a sample of 19 young stars, brown dwarfs and sub-brown dwarfs showing mid-infrared excess emission. The resulting sample includes sources with luminosities of 0.5 > log(L * /L ⊙ ) > -3.1. Six of the more luminous sources in our sample have been previously identified by other surveys for young stars and brown dwarfs. Five of the sources in our sample have nominal masses at or below the deuterium burning limit (12 M J ). Over three decades in luminosity, our sources have an approximately constant ratio of excess to stellar luminosity. We compare our observed SEDs to theoretical models of a central source with a passive irradiated circumstellar disk and test the effects of disk inclination, disk flaring, and the size of the inner disk hole on the strength/shape of the excess. The observed SEDs of all but one of our sources are well fit by models of flared and/or flat disks.

No abstract