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We present deep CCS and HC$_7$N observations of the L1495-B218 filaments in the Taurus molecular cloud obtained using the K-band focal plane array on the 100m Green Bank Telescope. We observed the L1495-B218 filaments in CCS $J_N$ = 2$_1$$-$1$_0$ and HC$_7$N $J$ = 21$-$20 with a spectral resolution of 0.038 km s$^{-1}$ and an angular resolution of 31$''$. We observed strong CCS emission in both evolved and young regions and weak emission in two evolved regions. HC$_7$N emission is observed only in L1495A-N and L1521D. We find that CCS and HC$_7$N intensity peaks do not coincide with NH$_3$ or dust continuum intensity peaks. We also find that the fractional abundance of CCS does not show a clear correlation with the dynamical evolutionary stage of dense cores. Our findings and chemical modeling indicate that the fractional abundances of CCS and HC$_7$N are sensitive to the initial gas-phase C/O ratio, and they are good tracers of young condensed gas only when the initial C/O is close to solar value. Kinematic analysis using multiple lines including NH$_3$, HC$_7$N, CCS, CO, HCN, \& HCO$^+$ suggests that there may be three different star formation modes in the L1495-B218 filaments. At the hub of the filaments, L1495A/B7N has formed a stellar cluster with large-scale inward flows (fast mode), while L1521D, a core embedded in a filament, is slowly contracting due to its self-gravity (slow mode). There is also one isolated core that appears to be marginally stable and may undergo quasi-static evolution (isolated mode)., ApJ accepted

We present 107 maps of continuum emission at 350 microns from Galactic molecular clumps. Observed sources were mainly selected from the Bolocam Galactic Plane Survey (BGPS) catalog, with 3 additional maps covering star forming regions in the outer Galaxy. The higher resolution of the SHARC-II images (8.5" beam) compared with the 1.1 mm images from BGPS (33" beam) allowed us to identify a large population of smaller substructures within the clumps. A catalog is presented for the 1386 sources extracted from the 350 micron maps. The color temperature distribution of clumps based on the two wavelengths has a median of 13.3 K and mean of 16.3 +- 0.4 K, assuming an opacity law index of 1.7. For the structures with good determination of color temperatures, the mean ratio of gas temperature, determined from NH3 observations, to dust color temperature is 0.88 and the median ratio is 0.76. About half the clumps have more than two substructures and 22 clumps have more than 10. The fraction of the mass in dense substructures seen at 350 microns compared to the mass of their parental clump is ~0.19, and the surface densities of these substructures are, on average, 2.2 times those seen in the clumps identified at 1.1 mm. For a well-characterized sample, 88 structures (31%) exceed a surface density of 0.2 g cm^(-2), and 18 (6%) exceed 1.0 g cm^(-2), thresholds for massive star formation suggested by theorists., 76 pages, 26 figures, 6 tables. Fig. 25 shows the complete sample of 107 maps. Accepted for publication in ApJS. Full tables 3 and 5 will be available online through ApJS. Typos corrected and other small changes on text after journal proof-review

The Bolocam Galactic Plane Survey (BGPS) is a 1.1 mm continuum survey of dense clumps of dust throughout the Galaxy covering 170 square degrees. We present spectroscopic observations using the Heinrich Hertz Submillimeter Telescope of the dense gas tracers, HCO+ and N2H+ 3-2, for all 6194 sources in the Bolocam Galactic Plane Survey v1.0.1 catalog between 7.5 0.5 K) without HCO+ 3-2 emission does not occur in this catalog. We characterize the properties of the dense molecular gas emission toward the entire sample. HCO+ is very sub-thermally populated and the 3-2 transitions are optically thick toward most BGPS clumps. The median observed line width is 3.3 km/s consistent with supersonic turbulence within BGPS clumps. We find strong correlations between dense molecular gas integrated intensities and 1.1 mm peak flux and the gas kinetic temperature derived from previously published NH3 observations. These intensity correlations are driven by the sensitivity of the 3-2 transitions to excitation conditions rather than by variations in molecular column density or abundance. We identify a subset of 113 sources with stronger N2H+ than HCO+ integrated intensity, but we find no correlations between the N2H+ / HCO+ ratio and 1.1 mm continuum flux density, gas kinetic temperature, or line width. Self-absorbed profiles are rare (1.3%)., Accepted for publication in ApJS. The full velocity catalog and data tables (complete Tables 2,3, and 5) may be downloaded from http://eldora.as.arizona.edu/~yshirley/Arizona/BGPS/ Kinematic finder charts (0.5 deg x 0.5 deg) are also available at the same address

We present observations of six Class 0 protostars at 3.3 mm (90 GHz) using the 64-pixel MUSTANG bolometer camera on the 100-m Green Bank Telescope. The 3.3 mm photometry is analyzed along with shorter wavelength observations to derive spectral indices (S_nu ~ nu^alpha) of the measured emission. We utilize previously published dust continuum radiative transfer models to estimate the characteristic dust temperature within the central beam of our observations. We present constraints on the millimeter dust opacity index, beta, between 0.862 mm, 1.25 mm, and 3.3 mm. Beta_mm typically ranges from 1.0 to 2.4 for Class 0 sources. The relative contributions from disk emission and envelope emission are estimated at 3.3 mm. L483 is found to have negligible disk emission at 3.3 mm while L1527 is dominated by disk emission within the central beam. The beta_mm^disk, 19 pages, 3 figures, AJ accepted, in press

We present Spitzer observations of a sample of 12 starless cores selected to have prominent 24 micron shadows. The Spitzer images show 8 and 24 micron shadows and in some cases 70 micron shadows; these spatially resolved absorption features trace the densest regions of the cores. We have carried out a 12CO (2-1) and 13CO (2-1) mapping survey of these cores with the Heinrich Hertz Telescope (HHT). We use the shadow features to derive optical depth maps. We derive molecular masses for the cores and the surrounding environment; we find that the 24 micron shadow masses are always greater than or equal to the molecular masses derived in the same region, a discrepancy likely caused by CO freeze--out onto dust grains. We combine this sample with two additional cores that we studied previously to bring the total sample to 14 cores. Using a simple Jeans mass criterion we find that ~ 2/3 of the cores selected to have prominent 24 micron shadows are collapsing or near collapse, a result that is supported by millimeter line observations. Of this subset at least half have indications of 70 micron shadows. All cores observed to produce absorption features at 70 micron are close to collapse. We conclude that 24 micron shadows, and even more so the 70 micron ones, are useful markers of cloud cores that are approaching collapse., 41 pages, 28 figures, 5 tables; accepted by ApJ

I review the basic processes that may be used to develop a chemical evolutionary sequence for low-mass starless cores. I highlight observational results from the Arizona Radio Observatory-Green Bank Survey. Observations were performed with the SMT 10-m, ARO 12-m, and GBT 100-m toward a sample of 25 nearby (D < 400 pc) low-mass starless cores which have radiative transfer models of the 850 $��$m emission and observed SED (160 - 1300 um). The cores were observed in the lines of NH3 (1,1) and (2,2), o-NH2D 1_{11} - 1_{01}, C2S 1_2 - 2_1, C3S 4 - 3, HCN 1 - 0, HC5N 9 - 8, HC7N 21 - 20, C18O and C17O 2 - 1, and p-H2CO 1_{01} - 0_{00}., To appear in "Molecules in Space & Laboratory", Paris 2007, eds. J.L. Lemaire & F. Combes. Corrected typo, otherwise "more or less" the same

Studying the physical environments of low mass and high mass cores using dust continuum emission provides important observational constraints on theoretical models of star formation. The motivation and procedure for modeling dust continuum emission is reviewed and the results of recent surveys towards low mass and high mass star forming regions are compared., Comment: 5 pages, 3 figures. To appear in Galactic Star Formation Across the Stellar Mass Spectrum, ASP conf. series, ed. James M. De Buizer

Our knowledge of the initial conditions and early stages of high mass star formation is very limited. We will review recent surveys of regions in the early stages of massive star formation using molecular tracers of high density and dust continuum emission and consider the status of evolutionary schemes. Comparison to the situation for low mass, relatively isolated star formation will be used to illustrate the outstanding issues in massive star formation. The problem of initial conditions is particularly acute because there is a lack of observational evidence for regions capable of forming massive stars BEFORE star formation actually begins. By analogy with the Pre-Protostellar Cores (PPCs) studied for low-mass star formation, one might call such regions Pre-Proto-cluster Cores (PPclCs). We will conclude with some speculation about what such cores might look like and possibilities for their detection., 14 page review to appear in Hot Star Workshop III: The Earliest Phases of Massive Star Birth, ASP Conference Series, 2002, ed. P.A. Crowther. See http://peggysue.as.utexas.edu/yshirley/papers.html for poster contributions

We present the results of a multi-faceted study of the high-mass star-forming region S235. With the CalTech Submillimeter Observatory (CSO), we have observed and/or mapped over fifty molecular transitions and 350 micron dust emission in an attempt to learn more about the chemistry, kinematics, and mass distribution within this rich region. We have found two dust cores that are not resolved in our molecular line observations and suggest that one of these is a less evolved star-forming core., Comment: 2 pages to appear in Hot Star Workshop III: The Earliest Phases of Massive Star Birth, ASP Conference Series, 2002, ed. P.A. Crowther

In this survey we have systematically mapped 63 cloud cores in the CS J = 5 -> 4 line towards a sample of high mass star forming cores with water masers (Plume et al. 1992, Plume et al. 1997) using the CSO. From the CS spectra and maps we determine cloud core sizes, virial masses, a mass spectrum, and a size-linewidth relationship., 2 pages to appear in Hot Star Workshop III: The Earliest Phases of Massive Star Birth, ASP Conference Series, 2002, ed. P.A. Crowther

Twenty-four cores have been mapped in CS J = 7 -> 6 at the CSO. From the spectra we determine core sizes and virial masses. Combining results from the CS and dust continuum studies for M8E, we use Monte Carlo simulations for the CS emission to determine radial profiles., 2 pages to appear in Hot Star Workshop III: The Earliest Phases of Massive Star Birth, ASP Conference Series, 2002, ed. P.A. Crowther