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We used the 4 m Discovery Channel Telescope (DCT) at Lowell observatory in 2014 to observe the Guitar Nebula, an Hα bow-shock nebula around the high-velocity radio pulsar B2224+65. Since the nebula's discovery in 1992, the structure of the bow-shock has undergone significant dynamical changes. We have observed the limb structure, targeting the “body” and “neck” of the guitar. Comparing the DCT observations to 1995 observations with the Palomar 200-inch Hale telescope, we found changes in both spatial structure and surface brightness in the tip, head, and body of the nebula.

Larionov, V. M. et. al., After several years of quiescence, the blazar CTA 102 underwent an exceptional outburst in 2012 September-October. The flare was tracked from gamma-ray to near-infrared (NIR) frequencies, including Fermi and Swift data as well as photometric and polarimetric data from several observatories. An intensive Glast-Agile support programme of the Whole Earth Blazar Telescope (GASP-WEBT) collaboration campaign in optical and NIR bands, with an addition of previously unpublished archival data and extension through fall 2015, allows comparison of this outburst with the previous activity period of this blazar in 2004-2005. We find remarkable similarity between the optical and gamma-ray behaviour of CTA 102 during the outburst, with a time lag between the two light curves of approximate to 1 h, indicative of cospatiality of the optical and gamma-ray emission regions. The relation between the gamma-ray and optical fluxes is consistent with the synchrotron self-Compton (SSC) mechanism, with a quadratic dependence of the SSC gamma -ray flux on the synchrotron optical flux evident in the post-outburst stage. However, the gamma -ray/optical relationship is linear during the outburst; we attribute this to changes in the Doppler factor. A strong harder-when-brighter spectral dependence is seen both the in gamma-ray and optical non-thermal emission. This hardening can be explained by convexity of the UV-NIR spectrum that moves to higher frequencies owing to an increased Doppler shift as the viewing angle decreases during the outburst stage. The overall pattern of Stokes parameter variations agrees with a model of a radiating blob or shock wave that moves along a helical path down the jet., The St. Petersburg University team acknowledges support from Russian RFBR grant 15-02-00949, and St. Petersburg University research grants 6.38.335.2015 and 6.42.1113.2016. The research at Boston University was funded in part by NASA Fermi Guest Investigator grants NNX08AV65G, NNX10AO59G, NNX10AU15G, NNX11AO37G, NNX11AQ03G, and NNX14AQ58G. The research at Steward Observatory was funded in part by NASA Fermi Guest Investigator grants NNX09AU10G and NNX12AO93G. Acquisition of the MAPCAT data at Calar Alto is performed at the IAA-CSIC and is supported by the Spanish Ministry of Economy and Competitiveness (MINECO) grant AYA2013-40825-P.This research was partially supported by the Scientific Research Fund of the Bulgarian Ministry of Education and Sciences under grant DO 02-137 (BIn-13/09). The Maidanak Observatory team acknowledges support from Uzbekistan Academy of Sciences grant F2-FA-F027.

A systematic and automated search of the extensive GLIMPSE mid-infrared survey data of the inner Galaxy was carried out to uncover new star clusters. This search has yielded 59 new clusters. Using our automated search algorithm, these clusters were identified as significant localized overdensities in the GLIMPSE point-source catalog (GLMC) and archive (GLMA). Subsequent visual inspection of the GLIMPSE image mosaics confirmed the existence of these clusters plus an additional 33 heavily embedded clusters missed by our detection algorithm, for a total of 92 newly discovered clusters. These previously uncataloged clusters range in type from heavily embedded to fully exposed clusters. More than half of the clusters have memberships exceeding 35 stars, and nearly all the clusters have diameters of 3' or less. The Galactic latitude distribution of the clusters reveals that the majority are concentrated toward the Galactic midplane. There is an asymmetry in the number of clusters located above and below the midplane, with more clusters detected below the midplane. We also observe an asymmetry in the number of clusters detected in the northern and southern halves of the Galaxy, with more than twice as many clusters detected in the south.

Examination of early, in-orbit checkout (IOC) images of a portion of the Galactic plane obtained by the Infrared Array Camera (IRAC) aboard the Spitzer Space Telescope revealed the presence of an extended emission nebula with internal structure. The Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE) data show this nebula, located at l � 42 � and b � 0N5, contains bright point sources and two nonstellar regions. Ancillary data sets were used to help reveal the nature of this nebula and its exciting objects. In particular, 13 CO J ¼ 1 ! 0 line emission mapped by the Galactic Ring Survey (GRS) shows molecular gas associated with the infrared nebula. The 13 CO radial velocity yields a far-kinematic distance of 11.1 kpc to the nebula, since there is no evidence for H i self-absorption. At 11.1 kpc, the far-infrared luminosity of the nebula is 4:8;10 4 L� , and the mass of its molecular cloud is 1:1;10 4 M� . The spectral energy distribution rises steeply from 2.2 to 100 � m with an absorption feature at 10 � m, exhibiting the shape of a late Class 0 young stellar object (YSO). The radio continuum flux observed toward the nebula is consistent with the free-free emission from one or more massive YSOs (MYSOs) with spectral types in the range O9 to B0. This analysis demonstrates one technique the GLIMPSE team will use for revealing thousands of Galactic star formation regions.

We have imaged five dense molecular cores, selected from the Galactic Ring Survey (GRS), in the mid-infrared with the MIRAC3 instrument. We obtained high spatial resolution (~1'') images through narrowband filters at 12.5 and 20.6 μm. Four of the five cores show multiple compact sources, extended structure, or both. Lower resolution observations by the Infrared Space Observatory (ISO) and the Midcourse Space Experiment (MSX) suggest that the fifth core is also surrounded by extended emission on large scales (2'). The extended mid-infrared structure is well-correlated with the radio continuum morphology in each of the five cores. This similarity suggests that the hot dust traced by the mid-infrared is located within the H II region, traced by the radio continuum, and not merely in a surrounding photodissociation region or molecular cloud. If a single exciting source is assumed for each core, estimates of the zero-age main-sequence spectral types based on the infrared luminosities are typically 1-2 spectral types earlier than those based on the radio free-free emission. However, allowing for multiple exciting sources and apportioning the far-infrared and radio fluxes to the component sources according to the mid-infrared flux distribution produces better agreement between the derived spectral types, with an average difference of less than half a spectral type.

Kinematic distance determinations in the inner Galaxy are hampered by the near-far kinematic distance ambiguity. Here we resolve the ambiguity for 49 H II region complexes with known recombination-line velocities in the first Galactic quadrant. We measured the 21 cm H I absorption spectrum toward each source with the Very Large Array in the C array. The maximum velocity of H I absorption was used to discriminate between the near and far kinematic distances. The number ratio of far to near sources, ~3, can be entirely explained as a geometrical effect. The kinematic distances that we derive are compared with previous determinations for the same sources. Although our distance determinations are largely in agreement with previous measurements, there are 22 discrepancies that we discuss. Using our distance determinations, we create a face-on Galactic map of the H II region complexes and compare it with a kinematically derived profile of the distribution of CO-traced molecular hydrogen. The H II region complexes delineate the large-scale features seen in the molecular gas. The 5 kpc molecular ring and the Sagittarius spiral arm are clearly evident, and a few H II region complexes lie in the Perseus arm.

We report on a three-dimensional (l, b, VLSR) physical association of H I self-absorption with 13CO emission toward the Galactic molecular cloud GRSMC 45.6+0.3. Photochemical models indicate that a significant column density of cool (T 25 K) H I exists in the skins (Av 2) of typical Galactic molecular clouds. The H I self-absorption can thus be produced by the cool cloud skin absorbing the warm (TSPIN ~ 100 K) background H I emission that is ubiquitously distributed throughout the Galaxy. Liszt, Burton, and Bania have suggested that because cool H I in a molecular cloud will absorb warmer H I background line emission, H I self-absorption can be used to resolve the kinematic distance ambiguity for molecular clouds in the inner Galaxy. Clouds at the near distance should show H I self-absorption, whereas clouds at the far distance will not since there is no background to absorb. The near kinematic distance of 1.8 kpc for the GRSMC 45.6+0.3 molecular cloud is independently confirmed by its morphological correlation with foreground optical extinction.

We present a study of the structure of four molecular clouds from the Milky Way Galactic Ring Survey (GRS), a Boston University and Five College Radio Astronomy Observatory collaboration. The GRS is a new high-resolution survey in the 13CO J = 1 → 0 spectral line of the inner Galaxy and the 5 kpc ring, the Milky Way's dominant star-forming structure. Because of the smaller line widths of 13CO compared to 12CO, we can avoid velocity crowding and establish accurate kinematic distances to the clouds. The kinematic distance ambiguity in the first Galactic quadrant is resolved using self-absorption in complementary high-resolution atomic hydrogen data. The four clouds are selected to span a large range of star formation activity, from the quiescent cloud GRSMC 45.60+0.30, which shows no signs of high-mass star formation, to W49, the most luminous star-forming region in the Galaxy. We use a three-dimensional Gaussian clump decomposition to identify clumps in the clouds and to investigate their properties. Each cloud has the same clump mass spectrum, dN/dM ∝ M-1.8, independent of star formation activity. We do not find significant differences in the slopes of the relations of density, line width, and clump mass as a function of clump size among the clouds. The size-density and size-line width relations show considerable scatter. Compared to the conventional Larson scaling laws, we find systematically flatter slopes for the size-density and size-line width relations and a higher power-law index for the size-mass relation. In particular, the clump line widths for the most quiescent cloud GRSMC 45.60+0.30 are independent of clump size. While the clouds as a whole are gravitationally bound, most of the clumps are not; only a small fraction of the total number of clumps is self-gravitating. The active star-forming clouds have a higher fraction of gravitationally bound clumps and a higher mean cloud volume density than the more quiescent clouds. The gravitationally unbound clumps are possibly confined by the weight of the self-gravitating complex. The pressures needed to bind these clumps are largest for the active star-forming clouds, which have a much higher weight than the quiescent clouds. Alternatively, a high number of the gravitationally unbound clumps may be transient.

We report the discovery of two distant embedded young stellar clusters located far in the outer Galaxy. The clusters are resolved in near-infrared images and seen as enhancements in the surface density of IR-excess stars centered close to IRAS 07255-2012. The clusters are embedded in a molecular cloud containing a CS dense core. The molecular cloud, as traced by CO (J = 1-0) is elongated and extends over a region of 15 × 6 pc2. From the millimeter observations, we derive a kinematic distance of 10.2 kpc and a Galactocentric distance of 16.5 kpc, making these clusters among the most distant embedded clusters in the Galaxy. The main (richer) cluster is well confined to a region of about 1.2 pc in radius. Down to our detection limit of about 1-2 M☉ at this distance, it contains at least 30 members. The smaller cluster contains at least five stars. They all exhibit near-infrared color excesses consistent with young stellar objects having circumstellar and/or envelope material. We estimate that the star formation efficiency of this molecular cloud is about 4%-10%.

We have conducted an HCN (J = 1–0) survey of 37 star-forming and quiescent dense cloud cores. HCN emission was detected toward 31 of the 33 cores containing embedded point sources, with only weak or no HCN detection among four starless sources. We find that the J = 1–0 transition of the HCN molecule is particularly well suited for revealing the early stages of star formation in molecular clouds. In the sample of star-forming cores, there is excellent spatial coincidence (better than 7'') between the position of the peak integrated HCN emission and the location of the associated young stellar object (YSO). Furthermore, emission strength in this HCN transition is well correlated with the YSO class: Class 0 and Class I YSOs are preferentially detected. Detecting strong (>1 K km s-1) HCN emission from a molecular cloud core indicates the presence of an embedded YSO and thus, indirectly, of a collapsing core. In addition, detection of very strong (>3 K km s-1) HCN emission implies an 80% likelihood of the presence of an embedded Class 0 YSO.

We present the results of a survey for CS emission toward a sample of 47 Bok globules selected from the catalog of Clemens & Barvainis. The globules were observed at the FCRAO 14 m, the SEST 15 m, and the IRAM 30 m telescopes in the CS J = 2 → 1 transition. Additionally, higher spatial resolution (11''-30'') observations in the CS J = 3 → 2 and 5 → 4 lines, as well as the C34S J = 2 → 1 and 3 → 2 lines, were carried out toward a subsample of 20 globules using the IRAM 30 m and the CSO 10 m telescopes. Two-thirds of the globules were detected in the CS J = 2 → 1 line. The detection rate was higher in globules with IRAS sources (72%) than in globules without IRAS sources (44%). The detection rate was 100% for globules with embedded Class 0 and Class I infrared sources, dropping to 60% for Class II-D sources and to 40% for Class II sources. These results support the association of dense cores with IRAS point sources in Bok globules and indicate that the dense gas is most apparent in the early stages. We present CS maps of 12 globule cores and derive sizes for nine CS cores. The results of the CS survey are compared with the results of surveys of other lines and of dust continuum emission. The integrated intensities of the CS lines correlate with those of C18O J = 2 → 1, but the line widths and FWHM sizes tend to be somewhat larger than those of C18O. The mean FWHM size of those sources with reasonable distance estimates is 0.41 ± 0.18 pc, and the mean virial mass is 60 ± 52 M☉. The mean size places them intermediate between cores in Taurus and cores associated with water masers and massive star formation.

A new method for determining distances to dark clouds and small Bok globules based on broadband optical photometry has been developed. The method exploits the fact that M dwarf stars do not redden into the colors of other main-sequence stars. Consequently, from analysis of color-color diagrams of V-I versus B-V, spectral types and extinctions of faint M dwarf stars located in front of and behind the molecular clouds can be established. For sufficiently deep observations (B ≈ 20–24 mag), distances to clouds closer than about 1 kpc can be bracketed to a higher degree of precision (10–40 pc) than previously possible. Photometric data for the Bok globule CB 24 are used in this paper to demonstrate this method, yielding a maximum distance of 360 pc.

We have performed a near-infrared JHK survey of a dense core and a diffuse filament region within the filamentary dark cloud GF 9 (LDN 1082). The core region is associated with the IRAS point source PSC 20503+6006 and is suspected of being a site of star formation. The diffuse filament region has no associated IRAS point sources and is likely quiescent. We find that neither the core nor the filament region appears to contain a Class I or Class II young stellar object. As traced by the dust extinction, the core and filament regions contain 26 and 22 solar mass, respectively, with an average H2 volume density for both regions of approximately 2500/cu cm. The core region contains a centrally condensed extinction maximum with a peak extinction of A(sub v) greater than or approximately equal to 10 mag that appears to be associated with the IRAS point source. The average H2 volume density of the extinction core is approximately 8000/cu cm. The dust within the filament, however, shows no sign of a central condensation and is consistent with a uniform-density cylindrical distribution.

We have conducted an HCN (J = 1–0) survey of dense cores in a sample of 24 star-forming and quiescent Bok globules. HCN emission was detected toward 11 of 13 globules containing embedded point sources, with no HCN detection among 11 starless globules. As in other dark clouds, the J = 1–0 hyperfine line intensity ratios vary from globule to globule and also with position toward the same globule, suggesting the presence of either a scattering envelope surrounding the core or a complex density structure. We find that the J = 1–0 transition of the HCN molecule can be used effectively to search for early stages of star formation in small molecular clouds: in the sample of star-forming cores, for three (of five) sources mapped, there is good spatial coincidence (better than 6'') between the position of the peak integrated HCN emission and the location of the associated embedded source. Furthermore, this transition is well correlated with the young stellar object (YSO) class, detecting preferentially class I YSOs. Our results indicate that detecting strong (>1 K km s-1) HCN emission from a molecular cloud core seems to imply the presence of an embedded protostar and thus, indirectly, that of a collapsing core.

We present a study of the morphological aspects of H2 jets and knots seen toward the small dark cloud Sandqvist 136. Near-infrared images of this cloud in the J, H, and K bands and in the 2.12 μm v = 1-0 S(1) molecular hydrogen line were obtained. The images reveal the presence of a near-infrared nebula with a conical shape. The location of the apex of the cone, in the K-band image, coincides with the position of an IRAS Point Source Catalogue source. This source, possibly a class 0 young stellar object, is likely to be the illuminator of the nebula. The position and orientation of the conical nebula coincide with those of the blueshifted lobe of the previously found molecular outflow associated with Sandqvist 136. Near-infrared jets and knots were found positionally associated with the high-velocity molecular outflow. The knots seem to be tracing the walls of a cavity excavated by the molecular outflow. Unlike most outflows commonly associated with class 0 sources, the outflow associated with this source appears to be poorly collimated.

A catalog of 248 small molecular clouds selected from the northern hemisphere Palomar Observatory Sky Survey has been assembled. These clouds have angular sizes of less than 10 arcmin (the mean of the sample is 4 arcmin), are reasonably well-isolated, and centrally opaque. They most closely resemble small versions of the larger Bok globules and Barnard objects. Many (30%) of the smallest members of this catalog have not been previously cataloged or studied. Coordinates accurate to 0.5 arcmin, optical extents and orientation angles, and cross-references are given for all of the clouds. Radial velocities, obtained from CO observations, are listed for 158 of the clouds. Additionally, 339 associated or possibly associated IRAS point sources are listed for 147 of the clouds. As most of these clouds have few or no foreground stars and subtend small angular extents, they are likely the smallest (all < 1.5 pc) and simplest dark molecular clouds near the Sun. The mean ellipticity (b) of the clouds in the catalog is 2.0, indicating that spherical cloud models may not be appropriate for this sample. The mean orientations, with respect to the galactic plane, of the clouds showing ellipticities greater than unity has no angular dependence; that is, the local galactic plane does not seem to order the direction of the optically determined ellipticity for the clouds. The far-infrared properties of the clouds with associated IRAS sources are similar to those seen in the sample of dark cloud cores studied by Beichman et al. (1986) [Ap. J., 307, 337], but are somewhat cooler (19 K vs 28 K for the means) and less FIR bright. Millimeter 12CO (J = 2-1) observations of the centers of 93 of the cataloged clouds shows that most (70%) of the sample are cool (gas kinetic temperature ∼8 K) and quiescent (gas dynamical motions ≈ sonic). Some clouds exhibit warmer gas temperatures possibly driven by radiative heating from nearby stars. Another small group of clouds exhibit the cool temperatures and supersonic linewidths characteristic of active embedded protostellar collapse or outflow.

In Spitzer/IRAC images obtained under the GLIMPSE Legacy Survey, we have identified a unique and provocative nebular object we call the "Southern Jellyfish Nebula." The Southern Jellyfish Nebula is characterized by a fan of narrow tendrils with extreme length-to-width ratios that emanate from the vicinity of a bright infrared point source embedded in a smaller resolved nebula. From CO observations of the Nebula's morphologically associated molecular cloud, we have derived a kinematic distance of 5.7 ± 0.8 kpc and a cloud mass of 3.2 ± 0.9 × 10^3 M_⊙. The tendril-like ropes of the Nebula have widths of ~0.1 pc and lengths of up to ~2 pc. We have integrated the infrared spectral energy distribution (SED) of the point source to establish it as a massive young stellar object (MYSO), most likely forming alone, but possibly masking fainter cluster members. The shape of the SED is consistent with the shape of a late Class 0 SED model. Based on its far-IR luminosity of 3.3 ± 0.9 × 10^4 L_⊙, the Southern Jellyfish's MYSO has a zero-age main sequence (ZAMS) spectral type of B0. Given the curious nature of this nebula, we suspect its peculiar IR-bright structure is directly related to its current state of star formation.

Using the SEQUOIA multi-pixel array receiver on the Five College Radio Astronomy Observatory (FCRAO) 14 m telescope, we are conducting a new molecular line survey of the inner Galaxy. The Boston University (BU)-FCRAO Galactic Ring Survey (GRS) will map 13CO (1-0) emission from l = 15° to 52° and b = -1° to 1°. Compared with previous molecular line surveys of the inner Galaxy, the GRS offers excellent sensitivity, better spectral resolution, the same or better angular resolution, Nyquist sampling, and the use of 13CO (1-0), a better column density tracer than 12CO.

The Space Infrared Telescope Facility (SIRTF), a 0.85-meter, cryogenically-cooled telescope, will be launched in 2002. SIRTF will extensively make use of large-format detector arrays. These, combined with the sky visibility of SIRTF’s solar orbit will facilitate significant surveys. SIRTF surveys will complement observations by NASA’s other Great Observatories and will enable follow-up SIRTF studies. Data from the large, “SIRTF Legacy Science Program” will be made widely available, on a rapid, non-proprietary release, to the general astronomical community.

Fifteen small, apparently starless Bok globules were mapped at high spatial and spectral (0.007 km s−1 channel−1) resolution in the (J=1→0) rotational line of 13CO using the 14 m radio telescope of the Five College Radio Astronomy Observatory, and the fifteen-element 3 mm array receiver QUARRY. From 120 to 360 positions per globule, sampled with half-beam spacing, were observed in the 13CO line. Gaussian fitting of the emission lines was used to establish mean radial velocities and uncertainties. Each globule radial velocity distribution on the sky was fit to a plane (solid body rotation) to yield mean velocity gradients with position, and rotation axis directions. The globules are rotating at rates about 30 times faster than velocity shifts attributable to local differential Galactic rotation. For globule assumed mean distances of 600 pc, the gradients range in a distinctly bimodal distribution, from 0.089 km s−1 pc−1 (ω∼3×10−15 s−1) to 0.950 km s−1 pc−1 (ω∼3×10−14 s−1). Detailed examination of the globu...

Recent high resolution surveys with the ISO and MSX satellites have revealed a large number of Galactic clouds with significant extinction in the midinfrared. The infrared dark clouds are characterized by their high masses, high column densities, and low temperatures. Little is known, however, about their origin and distribution in the Galaxy. We use MSX mid-IR data to catalog IR dark cloud and core candidates in the first and fourth Galactic quadrants. The distribution of IR dark clouds is concentrated around the Galactic mid-plane and traces prominent bright star forming regions. Selected high contrast IR dark clouds in the first Galactic quadrant are correlated with 13CO emission from the Galactic Ring Survey to spectroscopically determine their distances. The majority of IR dark clouds is found towards the 5 kpc Galactic Ring. We suggest that the condensations in the most massive IR dark clouds represent high mass proto-clusters, or OB-associations in the making.

After a few years of quiescence, the blazar CTA 102 underwent a large outburst in the fall of 2012. The flare has been tracked from γ-rays to near-infrared, including Fermi and Swift data as well as polarimetric data from several observatories. An intensive GASP-WEBT collaboration campaign in optical and NIR bands, with the addition of previously unpublished archival data, allows comparison of this outburst with the previous activity period of this blazar in the early 2000s. We find remarkable similarity between the optical and γ-ray behavior of CTA 102 during the outburst, without any time lag between the two light curves, indicating co-spatiality of the optical and γ-ray emission regions. A strong harder-when-brighter spectral dependence is seen both in γ-rays and optical. The polarimetric behavior of CTA 102 during the outburst conforms with a shock-in-jet interpretation.

The scientific motivation, data collection strategy, data reduction, and analysis methods are presented for the Galactic Plane Infrared Polarization Survey (GPIPS). The chief goal for the Survey was to reveal the nature of the magnetic field threading the Galactic disk, in particular through regions of low to moderate extinction (1-20 mag of A{sub V} ) and star formation in the cool interstellar medium. The Survey region spans 76 deg{sup 2} of the northern Milky Way disk, from l = 18 Degree-Sign to 56 Degree-Sign and b =-1 Degree-Sign to +1 Degree-Sign . Linear polarimetric imaging observations began in 2006 in the near-infrared H band (1.6 {mu}m) using the Mimir instrument on the 1.8 m Perkins telescope, located outside Flagstaff, AZ. Mimir used a cold, fixed wire grid and a rotateable cold, compound half-wave plate to obtain 'step-and-integrate' polarimetry over its full 10 Multiplication-Sign 10 arcmin field of view. The GPIPS bright and faint polarimetric limits are approximately 7th and 15th mag, respectively, set by saturation and photon noise. Polarimetric uncertainties track with stellar magnitude, from about 0.1% to 25%, on average, from the brightest to faintest stars. Across the 3237 field GPIPS region, approximately 0.5 million stars are estimated tomore » show detectable linear polarization (P/{sigma}{sub P} > 3); most of these have m{sub H} < 12. This represents many orders of magnitude improvement in the number of polarization measurements across this region. GPIPS observations are more than 90% complete and should finish in 2012.« less

The Galactic Plane Infrared Polarization Survey (GPIPS) covers 76 deg{sup 2} of the first Galactic quadrant midplane, 18 Degree-Sign {

The L183 (= L134N) dark molecular cloud has been probed using deep near-infrared imaging polarimetry of stars to beyond 14 mag in H band (1.6 μm), using the Mimir instrument on the 1.83 m Perkins Telescope. Nearly 400 arcmin2 were surveyed, including the dense core in L183, as seen in WISE Band 3 (12 μm) extinction, and the near surroundings, revealing 35 stars with either detected polarizations or significant upper limits. Stars with detected polarizations are reddened if closer than 8 arcmin (0.25 pc at the 110 pc cloud distance) and unreddened beyond. The polarimetric sample probes as close to the core as 3 arcmin (0.1 pc), where AV ~ 14 mag. Compared to the relatively unextincted surrounding stars, the reddened stars show no increase in polarization with extinction, suggesting that all of the polarization is induced in the outer layers of the cloud. This 0.25 pc radius envelope magnetic field does show a strong interaction with the L183 dark cloud. The envelope field is also virtually perpendicular, on the plane of the sky, to the field seen at 850 μm, though more closely aligned with the rotation axis of the dense gas core. The physical size scale at which the envelope and the core magnetic fields either decouple from each other or strongly modify their directions must be inside the 0.1 pc region probed here.

In this paper we describe a powerful method for mapping the distribution of dust through a molecular cloud using data obtained in large-scale, multiwavelength, infrared imaging surveys. This method combines direct measurements of near-infrared color excess and certain techniques of star counting to derive mean extinctions and map the dust column density distribution through a cloud at higher angular resolutions and greater optical depths than those achieved previously by optical star counting. We report the initial results of the application of this method to a dark cloud complex near the cluster IC 5146, where we have performed coordinated, near-infrared, JHK imaging and (13)CO, C(18)O, and CS millimeter-wave, molecular-line surveys of a large portion of the complex. More than 4000 stars were detected in our JHK survey of the cloud. Of these, all but about a dozen appear to be field stars not associated with the cloud. Star count maps at J band show a striking and detailed anticorrelation between the surface density of J-band sources and CO and CS molecular-line emission. We used the (H-K) colors and positions of nearly 1300 sources to directly measure and map the extinction and thus trace the dust column density through the cloud at an effective angular resolution of 1 min .5. We report an interesting correlation between the measured dispersion in our extinction determinations and the extinction. Modeling this relation indicates that effects of small-scale cloud structure dominate the uncertainties in our measurements. Moreover, we demonstrate that such observations can be used to place constraints on the nature of the spatial distribution of extinction on scales smaller than our resolution. In particular, we show that models in which the dust is distributed uniformly or in discrete high-extinction clumps on scales smaller than (1 min .5) are inconsistent with the observations. We have derived extinctions at the same positions and at the same angular resolution (1 min .7) as our molecular-line observations. This enabled a direct comparison of (13)CO, C(18)O, and CS integrated intensities and column densities with A(sub V) for more than 500 positions in the cloud, corresponding to a range in A(sub V) between 0 to 32 mag of extinction. We found the integrated intensities of (13)CO, C(18)O, and CS to be roughly linearly correlated with extinction over different ranges of extinction. However, for all three molecules we find the scatter in the observed relations to be larger than can be accounted for by instrumental error, suggesting that there are large intrinsic variations in the abundances or excitation of the molecules through the cloud. Mean abundances for all the molecules relative to hydrogen were directly derived from the data. The ratio of (13)CO to C(18)O abundances was found to be significantly higher than the terrestrial ratio in regions where extinction is less than 10 mag. In the same region, the dispersion in the abundance ratio is also found to be very large, suggesting that the abundances of one or both molecules are very unstable even at relatively large cloud optical depths. Beyond 10 mag of extinction the abundances of both species appear very stable with their ratio close to the terrestrial value.

The MILLIPOL polarimeter has been used to obtain 30-arcsec resolution 1300-micron data toward 10 cloud cores; the seven that were detected are associated with compact H II regions in massive molecular clouds. Cloud-core axis ratios and position angles were derived by examining the morphologies of IRAS-traced dust opacity structures. The MILLIPOL-detected cloud cores exhibit 1.5-3.2 core axis ratio values. The magnetic field is found to be generally perpendicular to the core dust distributions.

As part of a deep near-infrared imaging survey for infrared point sources in Bok globules, we have discovered the illuminator of the optical reflection nebula seen toward the Bok globule L810. The illuminator (L810 IRS) is located at the position predicted by Scarrott, Rolph, & Tadhunter from analysis of their optical polarimetry. This source is very red (J-K∼3.9) and bright (m K =10.7), and has an estimated bolometric luminosity of 890 L ○. . Additionally, we found a near-infrared nebula which extends 20″ symmetrically to the north and to the south of L810 IRS, exhibiting an hourglass shape

A multiwavelength study of the nearby small Bok globule LBN 11 is performed in order to investigate the relationship between embedded magnetic fields, cloud structure, and star formation. Optical polarimetry of background stars is used to characterize and trace the embedded magnetic field direction. High-dispersion CO isotopic mapping is employed to determine the radial density distribution of the gas, measure cloud rotation, and identify individual gas clumps. CS and SO mapping revealed dense cores within the (C-13)O clumps. Analysis of coadded IRAS images reveal the cloud to be free of current or recent star formation: there are no IR point sources of sufficient flux or proper colors to signify young stars associated with the cloud. The molecular line maps show the cloud to be extremely clumpy. Clumps are found to range in size from 0.2 pc for the largest CO clump to about 0.04 pc for the smallest CS feature. It is concluded that, at least in the envelope of the cloud, the magnetic field and the CO clumps are coupled.

The results of a successful search for outflows associated with low-mass young stellar objects (YSOs) in a sample of 41 small Bok globules are presented. This search was performed in the 12 CO J=1-0 spectral line using the new multibeam receiver (QUARRY) of the Five College Radio Astronomy Observatory. New outflows are found in about one-third of the sample (14 of 41). In addition, five globules are found to be rotating, with velocity gradients in the range 0.1-0.7 km/(s × arcmin)

The entire sample of small molecular clouds cataloged by Clemens and Barvainis (1988) has been probed using deep, coadded IRAS survey data analysis and (C-12)O spectroscopy. The far-IR colors are similar to those found for other amorphous Galactic constituents. The mean 12.25 micron color was 0.01, the mean 25/60 micron color was 0.68, and the mean 60/100 micron color was 0.70. The bulk of the dust mass was colder than 30 K. A very strong anticorrelation was found between dust optical depth and 60/100 micron color temperature. The mean far-IR luminosity of the sample is about 6.4 solar luminosities, the mean cloud mass is about 11 solar, the radius is around 0.35 pc, and the density is around 1000 H2/cu cm. Upper and lower limits for the number of these clouds in the Galaxy are 160,000 and 650,000. A total Galactic mass in Bok globules of about 3.5 million solar and a total luminosity of about two million solar is found. 45 refs.

A large sample of optically selected, small molecular clouds (Bok globules) has been probed using IRAS coadded images to search for associated young stellar objects. The IRAS images were examined for point sources located within the boundaries of the optical and infrared extents of 248 clouds. A total of 57 of the globules (23 percent of the sample) show evidence for associated point sources. From a comparison of the 12- and 25-micron fluxes of these objects, a distribution of spectral indices consistent with the presence of circumstellar dust is found. Similar analysis of other point sources within the IRAS images, but far from the globule boundaries, shows only normal stellar spectral indices. All young stars more massive than 0.7 solar masses were likely found. However, extrapolation of a Miller-Scalo (1979) initial mass function to the hydrogen-burning limit indicates that only about 20 percent of the total number of stars were found. It is therefore likely that almost every Bok globule harbors a young star. The inferred star formation efficiency is about 6 percent, again based on the Miller-Scalo initial mass function. Interestingly, this is the best test in 43 years of the conjecture made by Bok, that dust globules could represent the earliest stage of star formation. His conjecture was correct.

An instrument capable of measuring the polarization characteristics of weakly polarized, cold dust at millimeter and submillimeter wavelengths is presented in detail. The operation and calibration of this polarimeter at a wavelength of 1300 microns, configured for the NRAO 12-meter telescope, are discussed. Deep observations of Jupiter using this instrument revealed a main-beam instrumental polarization at, or below, the 0.2 percent level. Lunar limb observations revealed a sidelobe polarization sensitivity, in the range 0.25 percent - 1.0 percent. Further, through these efforts the nonthermal polarized flux from Jupiter at a level of about 0.04 percent of the thermal flux has been detected. Astronomical polarization measurements to 0.03 percent are possible, limited by the uncertainties in the instrumental polarization. This instrument has been primarily employed to measure and map magnetic-field directions in the very optically opaque cores of massive molecular clouds.

We report some preliminary results from the Massachusetts - Stony Brook CO survey of the first galactic quadrant using the 14-meter millimeterwave telescope of the Five College Radio Astronomy Observatory. The survey contains approximately 50 000 observations spaced every 3 arcminutes in 1 and b between longitudes 0° and 90° and latitudes -1° and 1°. We have mapped emission from giant molecular clouds (GMC) which we identified, in earlier more limited strip surveys of the galactic plane (Solomon, Sanders and Scoville 1979; Sanders 1981), on size scales from a few parsecs to hundreds of parsecs, in order to determine the degree of clustering and organization into large-scale features. In addition to the characteristic size of 20 – 60 pc for individual GMC, we find clustering of clouds on a scale of from 100 to 300 pc.

We report discovery of a new young stellar object driving a point-symmetric, near-infrared jet and molecular outflow. The YSO is associated with IRAS 06047 1117 and is embedded in a dense molecular cloud core located southeast of Orion A. The jet is seen in the H2 v =1 0 line at 2.12 m and extends over a total length of about0.4 pc. The driving source is optically invisible and has near-infrared colors and a spectral energy distribution consistent with a Class I source with an estimated luminosity of 6 L. Two Herbig-Haro objects are seen in H images located close to the positions of maximum H2 emission.

A compilation of CO emission regions and their measured parameters is presented which represents a nearly complete accounting of the molecular clouds in the first quadrant of the Galaxy. Emission regions associated with radio H II regions have systematically brighter CO peaks that are a factor of two to three times larger and have twice the mean velocity dispersion as the general cloud population. Both the H II region clouds and the hot core regions have a Galactic distribution characteristic of a spiral arm population, whereas the colder clouds are much less confined in Galactic azimuthal angle. Virial masses are obtained for the large sample of clouds with assigned kinematic distances. The mean H2 density for a GMC of diameter 40 pc is 180/cm. For these clouds, a linear relationship is found between the H2 column density and the integrated CO emission. The variation in the Z-dispersion of clouds as a function of cloud mass suggests that more massive GMCs have smaller random velocities.

We have detected v = 1, J = 5-4 SiO maser emission from R Leo, chi Cyg, and VX Sgr and v = 2, J = 4-5 maser emission from VX Sgr. Upper limits are reported for maser emission in the J = 6-5, v = 1 and v = 2, and J = 2-1, v = 3 transitions toward several late-type stars. Maser photon emission rates for the high J transitions which have been detected are roughly comparable to emission rates for the lower J transitions. Various maser pump mechanisms and emission regions are discussed, and published numerical models are compared with the observations. No single model emerges as the best explanation of SiO maser phenomena.

Optical and near-infrared photometry in the VRIJHK and CO (2.35 microns) bands and optical spectroscopy and polarimetry reveal that the optical counterpart of the X-ray source H0253+193 is most likely a RS CVn binary system. The results show a visual extinction of 11.3 mag to the star, with an IR excess possibly due a cooler binary companion or circumstellar material. It is suggested that the I-band polarization of 8.1 + or - 1.8 may be induced in the starlight by passage through the molecular cloud. The lack of strong H-alpha emission in the optical spectrum argues against the possibility of a classical T Tauri star, and the IR excess argues against a naked T Tauri star. The wide energy spectrum found in the dereddened optical and near-infrared photometry supports the binary star model.