Search

The water-vapor maser emission in the source G10.6-0.4 associated with an active starforming region (OB star cluster) is analyzed. The maser was monitored from 1981–2004 using the 22-meter radio telescope of the Pushchino Radio Astronomy Observatory. Statistical processing of the results revealed the presence of structural formations on various scales. The individual H2O maser features may form ordered structures with velocity (V LSR) gradients, localized in separate clusters of maser features. The statistical variations of the V LSR values for the maser components may be due to the accretion of material onto the OB star cluster in G10.6-0.4 together with the rotation of the molecular cloud core. A model with a rotating, nonuniform condensation of accreted material in the vicinity of the stellar cluster is proposed to explain the variations of the velocity centroid of the H2O spectra. The integrated flux variations are explained well by a model in which the central source is an OB star cluster, possibly containing five to six stars. An important role in the evolution of the maser emission, as well as of the source as a whole, may be played by turbulent motions of the gas.

Following the suggestion of Zuckerman et al. (2001, ApJ, 562, L87), we consider the evidence that 51 Eri (spectral type F0) and GJ 3305 (M0), historically classified as unrelated main sequence stars in the solar neighborhood, are instead a wide physical binary system and members of the young beta Pic moving group (BPMG). The BPMG is the nearest (d < 50 pc) of several groups of young stars with ages around 10 Myr that are kinematically convergent with the Oph-Sco-Cen Association (OSCA), the nearest OB star association. Combining SAAO optical photometry, Hobby-Eberly Telescope high-resolution spectroscopy, Chandra X-ray data, and UCAC2 catalog kinematics, we confirm with high confidence that the system is indeed extremely young. GJ 3305 itself exhibits very strong magnetic activity but has rapidly depleted most of its lithium. The 51 Eri/GJ 3305 system is the westernmost known member of the OSCA, lying 110 pc from the main subgroups. The system is similar to the BPMG wide binary HD 172555/CD -64d1208 and the HD 104237 quintet, suggesting that dynamically fragile multiple systems can survive the turbulent environments of their natal giant molecular cloud complexes, while still being imparted high dispersion velocities. Nearby young systems such as these are excellent targets for evolved circumstellar disk and planetary studies, having stellar ages comparable to that of the late phases of planet formation., 27 pages, 7 figures. Accepted for publication in the Astronomical Journal. For a version with high resolution figures, see http://www.astro.psu.edu/users/edf/51Eri.pdf

The mid-infrared emission from a photodissociation region (PDR) viewed edge-on in the Orion Nebula is examined through 8.7-20.6 ?m images and 8-13 ?m spectra. The polycyclic aromatic hydrocarbon (PAH) emission is located between the edges of H II regions and layers of [C I] emission, agreeing with PDR theory. Using a simple model, the spatial variations in the emission from PAHs detected at 8.6, 11.2, and 12.7 ?m are demonstrated to be directly proportional to the material column density and the intensity of the UV field. For a homogeneous, neutral cloud illuminated by a bright OB star, PDR theory predicts that the ultraviolet (UV) radiation is attenuated exponentially (e). The predicted UV attenuation is confirmed by observations of broad PAH emission features found at 8.6, 11.2, and 12.7 ?m. The PAH emission is found in cool regions having greater optical depths relative to regions where mid-infrared emission from ionized gas is observed. Through modeling we determine a gas density of 9.7 ? 104 cm-3. On large and small size scales, the relative strengths of the 8.6, 11.2, and 12.7 ?m PAH features at the bar of the Orion Nebula indicate that there is not a simple transition from ionized to neutral PAHs across the PDR.

X-ray spectroscopy of several OB stars with massive winds has revealed that many X-ray line profiles exhibit unexpectedly small blueshifts and are almost symmetric. Moreover, the hottest X-ray lines appear to originate closest to the star. These properties appear to be inconsistent with the standard model of X-rays originating in shocked material in line-driven spherically symmetric winds. Here we raise the question, can the X-ray line data be understood in terms of a two-component wind? We consider a scenario in which one component of the wind is a standard line-driven wind that emerges from a broad range of latitudes centered on the equator. The second component of the wind emerges from magnetically active regions in extensive polar caps. The existence of such polar caps is suggested by a recent model of dynamo action in massive stars. We describe how the two-component model is consistent with a variety of observational properties of OB star winds.

著者人数: 14名, Accepted: 2004-10-20, 資料番号: SA1003336000

A Monte Carlo method for detection of runaway OB stars from observational data is proposed. 61 runaway OB star candidates have been detected by an analysis of Hipparcos proper motions. The peculiar tangential and total transverse velocities have been determined for these stars. A list of the detected runaway star candidates is presented. The evidence of a discrepancy between photometric and parallactic distances of runaway OB star candidates is presented.

We explore the possibility that, in the vicinity of an OB star, a prestellar core which would otherwise have formed an intermediate or low-mass star may form a free-floating brown dwarf or planetary-mass object, because the outer layers of the core are eroded by the ionizing radiation from the OB star before they can accrete onto the protostar at the centre of the core. The masses of objects formed in this way are given approximately by $\sim 0.010 M_\odot (a_{\rm I} / 0.3 {\rm km} {\rm s}^{-1})^6 (\dot{\cal N}_{\rm Lyc} / 10^{50} {\rm s}^{-1})^{-1/3} (n_{\rm 0} / 10^3 {\rm cm}^{-3})^{-1/3} $, where $a_{\rm I}$ is the isothermal sound speed in the neutral gas of the core, $\dot{\cal N}_{\rm Lyc}$ is the rate of emission of Lyman continuum photons from the OB star (or stars), and $n_{\rm 0}$ is the number-density of protons in the HII region surrounding the core. We conclude that the formation of low-mass objects by this mechanism should be quite routine, because the mechanism operates over a wide range of conditions ($10^{50} {\rm s}^{-1} \la \dot{\cal N}_{\rm Lyc} \la 10^{52} {\rm s}^{-1}$, $10 {\rm cm}^{-3} \la n_0 \la 10^5 {\rm cm}^{-3}$, $0.2 {\rm km} {\rm s}^{-1} \la a_{\rm I} \la 0.6 {\rm km} {\rm s}^{-1}$) and is very effective. However, it is also a rather wasteful way of forming low-mass objects, in the sense that it requires a relatively massive initial core to form a single low-mass object. The effectiveness of photo-erosion also implies that that any intermediate-mass protostars which have formed in the vicinity of a group of OB stars must already have been well on the way to formation before the OB stars switched on their ionizing radiation; otherwise these protostars would have been stripped down to extremely low mass., 8 pages, 1 figure. to appear in A&A

The central region of the dark cloud L1482 is illuminated by LkHα 101, a heavily reddened (AV ≈ 10 mag) high-luminosity (≥8 × 103 L⊙) star having an unusual emission-line spectrum plus a featureless continuum. About 35 much fainter (mostly between R = 16 and >21) Hα emitters have been found in the cloud. Their color-magnitude distribution suggests a median age of about 0.5 Myr, with considerable dispersion. There are also at least five bright B-type stars in the cloud, presumably of about the same age; none show the peculiarities expected of HAeBe stars. Dereddened, their apparent V magnitudes lead to a distance of about 700 pc. Radio observations suggest that the optical object LkHα 101 is in fact a hot star surrounded by a small H II region, both inside an optically thick dust shell. The level of ionization inferred from the shape of the radio continuum corresponds to a Lyman continuum luminosity appropriate for an early B-type zero-age main-sequence star. The V - I color is consistent with a heavily reddened star of that type. However, the optical spectrum does not conform to this expectation: the absorption lines of an OB star are not detected. Also, the [O III] lines of an H II region are absent, possibly because those upper levels are collisionally deexcited at high densities. There are several distinct contributors to the optical spectrum of LkHα 101. The Hα emission line is very strong, with wings extending to about ±1700 km s-1, which could be produced by a thin overlying layer of hot electron scatterers. There is no sign of P Cygni type mass ejection. Lines of Si II are narrower, while the many Fe II lines are still narrower and are double with a splitting of about 20 km s-1. Lines of [Fe II], [O I], and [S II] are similarly sharp but are single, at the same velocity as the Fe II average. Work by Tuthill et al. allowed the inference, from K-band interferometry, that the central source is actually a small horseshoe-shaped arc about 005 (35 AU) across. A tipped annulus of that size in rotation about a 15 M⊙ star would produce double spectrum lines having about the splitting observed for Fe II. The totality of observational evidence encourages the belief that LkHα 101 is a massive star caught in an early evolutionary state.

We have investigated the relation between the orbital period Porb and the spin period Ps of neutron stars in OB/X-ray binaries. By simulating the time- development of the mass loss rate and radius expansion of a 20M donor star, we have calculated the detailed spin evolution of the neutron star before steady wind accretion occurs (that is, when the break spin period is reached), or when the OB star begins evolving o the main sequence or has filled its Roche lobe. Our results are compatible with the observations of OB/X-ray binaries. We find that in relatively narrow systems with orbital periods less than tens of days, neutron stars with initial magnetic field B0 stronger than about 3◊10 12 G can reach the break spin period to allow steady wind accretion in the main sequence time, whereas neutron stars with B0 < 3 ◊ 10 12 G and/or in wide systems would still be in one of the pulsar, rapid rotator or propeller phases when the companion evolves o the main sequence or fills its Roche lobe. Our results may help understand the various characteristics of the observed OB/neutron star binaries along with their distributions in the Ps Porb diagram.

New optical MK classification spectra have been obtained for 14 OB star candidates identified by Comeron et al. (2002) and presumed to be possible members of the Cyg OB2 cluster. All 14 candidate OB stars observed are indeed early-type stars, strongly suggesting the remaining 31 candidates identified by Comeron et al. are also early-type stars. However, as many as half of the new stars appear to be significantly older than the previously studied optical cluster, making their membership in Cyg OB2 suspect. Despite this, the recognition of Cyg OB2 being a more massive and extensive star cluster than previously realized, along with the recently recognized candidate super star cluster Westerlund 1 only a few kpc away (Clark & Negueruela 2002), reminds us that we are woefully under-informed about the massive cluster population in our Galaxy. Extrapolations of the locally derived cluster luminosity function indicate 10s to perhaps 100 of these very massive open clusters (Mcl ~ 10^4 M_sun, Mv ~ -11) should exist within our galaxy. Radio surveys will not detect these massive clusters if they are more than a few million years old. Our best hope for remedying this shortfall is through deep infrared searches and follow up near-infrared spectroscopic observations, as was used by Comeron et al. to locate candidate members of the Cyg OB2 association., 30 pages, 12 figures, ApJ in press

There is accumulating evidence for a strong link between nuclear starbursts and AGN. Molecular gas in the central regions of galaxies plays a critical role in fueling nuclear starburst activity and feeding central AGN. The dense molecular ISM is accreted to the nuclear regions by stellar bars and galactic interactions. Here we describe recent observational results for the OB star forming regions in M51 and the nuclear star burst in Arp 220 - both of which have approximately the same rate of star formation per unit mass of ISM. We suggest that the maximum efficiency for forming young stars is an Eddington-like limit imposed by the radiation pressure of newly formed stars acting on the interstellar dust. This limit corresponds to approximately 500 for optically thick regions in which the radiation has been degraded to the NIR. Interestingly, we note that some of the same considerations can be important in AGN where the source of fuel is provided by stellar evolution mass-loss or ISM accretion. Most of the stellar mass-loss occurs from evolving red giant stars and whether their mass-loss can be accreted to a central AGN or not depends on the radiative opacity of the mass-loss material. The latter depends on whether the dust survives or is sublimated (due to radiative heating). This, in turn, is determined by the AGN luminosity and the distance of the mass-loss stars from the AGN. Several AGN phenomena such as the broad emission and absorption lines may arise in this stellar mass-loss material. The same radiation pressure limit to the accretion may arise if the AGN fuel is from the ISM since the ISM dust-to-gas ratio is the same as that of stellar mass-loss.

We present mid-IR 21micron images of a sample of radio selected Ultracompact HII (UCHII) regions, obtained with the Midcourse Space Experiment (MSX). All, with one possible exception, are detected at mid-IR wavelengths, sampling the warm dust emission of the cocoons of the OB star central exciting sources. Many of the UCHII regions have nearby (up to a few pc distant) companion dust emission sources, which represent other potential star birth sites. In some objects the companion dominates the IRAS point source catalogue entry for the UCHII region. We compare the mid- and far-IR dust emission, measuring the embedded hot star luminosity, with published UCHII radio emission, measuring the Lyman continuum luminosity. We find a spectral type dependence, as predicted by the standard model of an ultracompact ionized hydrogen region, surrounded by a natal dust shell, with some scatter, which can be understood by consideration of: 1) dust absorption of some fraction of the emitted Lyman continuum photons; 2) fainter companion stars within the UCHII region; 3) the structure of the UCHII regions differing from star to star. Overall, the higher spatial resolution offered by MSX alleviates difficulties often encountered by comparison of IRAS far-IR fluxes with radio derived ionizing fluxes for UCHII regions., 22 pages, 15 figures (including 8 in Appendix), submitted to MNRAS

High signal-to-noise ratio, moderate-resolution spectra, providing full phase coverage of the 19-d WC6 + OB binary θ Mus (WR 48, HD 113904), have been obtained and show dramatic variations of the C III λ5696 emission-line profile. We have modelled these line profile variations using a purely geometrical model which assumes that the emission arises from two regions, an optically thin spherical shell around the WR star and a cone-shaped region that partially wraps around the OB star. The cone-shaped region represents the shock front arising from the collision between the winds of the two stars. This work builds upon our earlier study of WR 42 and WR 79, and uses a completely new code for the modelling, which includes the effects of turbulence. We now find much better agreement between the orbital inclination angles found for these stars with those determined using other methods. The fitting parameters found via modelling the C III λ5696 profile variations of θ Mus are used to infer that the OB companion most likely has a spectral type of 06V or 07V. The modelling presented here continues to show the exciting promise of a better understanding of WR star fundamental parameters.

We discovered that the Wolf-Rayet (WR)+OB star binary, WR 104, renowned for its associated "dusty pinwheel nebula" recently spatially resolved with infrared interferometry, exhibits strong quasi-periodic optical variations with a full amplitude of 2.7 mag. Such a large-amplitude, continuous variation has been unprecedented in a WR star. The optical quasi-period (~241 d) is in almost perfect agreement with the interferometric period (243.5+/-3 d). The remarkable agreement of the dominant period in optical variability with the orbital period supports that the strongly varying dust obscuration is physically related to the binary motion, rather than sporadic dust-forming episodes. Considering the low orbital inclination (11+/-7 deg) and the nearly circular orbit inferred from the interferometric observations, the strongly variable line-of-sight extinction suggests that the highly structured extinction can be being formed via an ejection of dust in the direction of the binary rotation axis. Another viable explanation is that the three-dimensional structure of the shock front, itself is the obscuring body. Depending on the geometry, the dusty shock front near the conjunction phase of the binary can completely obscure the inner WR-star wind and the OB star, which can explain the amplitude of optical fading and the past observation of remarkable spectral variation., 5 pages, 4 figures, to appear in PASJ (Letters), using an alternative style file

Stellar evolution models of massive stars are very sensitive to the adopted mass-loss scheme. The magnitude and evolution of mass-loss rates significantly affect the main sequence evolution, and the properties of post-main sequence objects, including their rotational velocities. Driven by potential discrepancies between theoretically predicted and observationally derived mass-loss rates in the OB star range, we particularly aim to investigate the response to mass-loss rates that are lower than currently adopted, in parallel with the mass-loss behavior at the "first" bi-stability jump. We perform 1D hydrodynamical model calculations of single $20 - 60 \, M_{\odot}$ Galactic ($Z = 0.014$) stars where the effects of stellar winds are already significant during the main sequence phase. We develop an experimental wind routine to examine the behavior and response of the models under the influence of different mass-loss rates. This observationally guided, simple and flexible wind routine is not a new mass-loss description but a useful tool based on the Wind-momentum Luminosity Relation and other scaling relations, and provides a meaningful base for various tests and comparisons. The main result of this study indicates a dichotomy when accounting for currently debated problems regarding mass-loss rates of hot massive stars. In a fully diffusive approach, and for commonly adopted initial rotational velocities, lower mass-loss rates than theoretically predicted require to invoke an additional source of angular momentum loss (either due to bi-stability braking, or yet unidentified) to brake down surface rotational velocities. [...]

We present the first quantitative UV spectroscopic analysis of resolved OB stars in IC1613. Because of its alleged very low metallicity (, Comment: ApJ, accepted. 50 pages, 13 figures

(first paragraph) We have obtained Halpha and Palpha emission line images covering the central 3 - 4 arcmin of M51 using the WFPC2 and NICMOS cameras on HST to study the high-mass stellar population. The 0.1 - 0.2 arcsec pixels provide 4.6 - 9 pc resolution in M51 and the Halpha/Palpha line ratios are used to obtain extinction estimates. A sample of 1373 Halpha emission regions is catalogued using an automated and uniform measurement algorithm. Their sizes are typically 10 - 100 pc. The luminosity function for the Halpha emission regions is obtained over the range L_{Halpha} = 10^{36} to 2 times 10^{39} erg s{-1}. The luminosity function is fit well by a power law with dN/dlnL proportional to L^{-1.01}). The power law is significantly truncated and no regions were found with observed L_{Halpha} above 2 times 10^{39} erg s^{-1} (uncorrected for extinction; the maximum seen in ground-based studies is approximately a factor of 5 higher, very likely due to blending of multiple regions). The extinctions derived here increase the maximum intrinsic luminosity to above 10^{40} erg s^{-1}). The logarithmically binned luminosity function is also somewhat steeper (alpha = -1.01) than that found ground-based imaging (alpha = -0.5 to -0.8) - probably also a result of our resolving regions which were blended in the ground-based images. The 2-point correlation function for the HII regions exhibits strong clustering on scales

We present ROSAT observations and analysis of thirteen superbubbles in the Large Magellanic Cloud. Eleven of these observations have not been previously reported. We have studied the X-ray morphology of the superbubbles, and have extracted and analyzed their X-ray spectra. Diffuse X-ray emission is detected from each of these superbubbles, and X-ray emission is brighter than is theoretically expected for a wind-blown bubble, suggesting that the X-ray emission from the superbubbles has been enhanced by interactions between the superbubble shell and interior SNRs. We have also found significant positive correlations between the X-ray luminosity of a superbubble and its H-alpha luminosity, expansion velocity, and OB star count. Further, we have found that a large fraction of the superbubbles in the sample show evidence of ``breakout'' regions, where hot X-ray emitting gas extends beyond the H-alpha shell., 25 pages, 8 figures, to be published in Astrophysical Journal Supplement Series

The spatial distribution of the youngest pulsars, with a characteristic age of less than 12,000 years, is considered. All the pulsars except for the pulsar in the Crab Nebula lie in groups of young OB stars. It is suggested that the precursor of the Crab pulsar was a rapidly rotating, massive OB star. The group of young massive stars from which the fast-moving star was ejected is indicated. Estimates of the age of the precursor of the Crab pulsar and of the age of the group of young stars from which it was ejected favor this hypothesis. It is concluded that the fast-moving star must have acquired a high velocity due to the dynamical evolution of the young stellar group.

In this paper we report the detection of CO ice at 4.67 μm toward Elias 25 in the ρ Ophiuchi cloud. The data were obtained using the UKIRT CGS4, and the CO-ice band is among the weakest yet observed. We compare our result to previous CO and H2O ice detections in an effort to understand the extinction thresholds for ice growth (Ath). Our data imply Ath < 11 magnitudes for CO ices in ρ Oph, much less than previously thought. We tentatively suggest that the OB star lines of sight reflect ice growth trends for pristine molecular cloud material not associated with star formation.

We present a high-angular resolution study of the cometary-shaped ultracompact H II region G29.96-0.02. We have obtained ~10'' angular-resolution millimeter-wave maps of the region in transitions of 13CO, C18O, CH3CN, CH3OH, and CS with the BIMA interferometer. We combine these data with complementary single-dish data of the 13CO, C18O, and CS lines taken with the FCRAO 14 meter telescope. These data are compared with near-infrared JHK-band images with ?09 angular resolution obtained with the Calar-Alto 3.5 m telescope. The 13CO data show emission extended over a 3 ? 2 pc region; however, the emission is strongly peaked near the head of the H II region. Strong CS, C18O, and CH3CN emissions peak near the same location. The CH3CN (J=6?5) emission peaks toward the hot core previously detected in VLA NH3(4, 4) observations, and we determine a kinetic temperature of 100 K in the core using a large velocity gradient analysis of the CH3CN (6?5) BIMA data and CH3CN/CH133CN (5?4) IRAM 30 m telescope data. We also find that the sharply peaked C18O, 13CO, and CS emission is indicative of a density gradient, with the peak density located in front of the head of the cometary H II region. We use our near-infrared data to search for sources embedded in the H II region and the adjacent cloud. In addition to the exciting star of the H II region, we identify a second star toward the head of the H II region with an extinction similar to that of the exciting star; this appears to be a second OB star in the H II region. Directly in front of the H II region we detect a highly reddened source, which is most likely a young star deeply embedded in the molecular gas. Furthermore, we find an enhanced density of sources with H-K >1 toward the molecular cloud and argue that these sources form an embedded cluster. Finally, we compare our results with current models of cometary shaped H II regions. Given the evidence that the G29.96 H II region exists in a gradient of molecular gas density that peaks in front of the head of the H II region, we favor the champagne flow model for this region. Comparing the measured densities, temperatures, and line widths of the ionized and molecular gas, we estimate the expansion speed of the H II region into the molecular core at 2-5 km s-1.

The classical Q-method for the brightest OB stars, the period-luminosity (P-L) relation for the Cepheids and the maximum magnitude-rate of decline (MMRD) relation for novae were used to study the absorption variations in M 31. An extinction map with 34 arcsec resolution was constructed. This resolution corresponds to a characteristic size of about 100 pc at which the colour excesses correlate most strongly. The mean colour excesses are E(B - V) = 0.51 f 0.27 mag from the OB stars, 0.21 f 0.09 mag from Cepheids and 0.14 f 0.10 mag from novae. The colour excess shows no big radial dependence within 12 kpc from the centre. The distributions of the colour excesses determined from OB stars (located predominantly in spiral arm regions) in six bins along the radius were compared with distributions generated via Monte Carlo simulation to estimate the optical thickness of the disk at different galactocentric distances. The total optical thickness of the disk is TB = 11.5 near the bulge and decreases to 2 in the outermost parts (R/& = 0.62, where R25 is the isophote diameter at B = 25 mag arcsec-2). We obtain a radial dust scale factor RD = 4.8 f 0.4 kpc. The constant ratio of the dust to OB star scale factors in the 2-direction was found to be (ZD/Z, = 1.25 f 0.25). We derived vertical scale factors 2s = 76 f 36 pc for the OB stars and ZD = 95f45 pc for the dust. The visible OB stars lay on a protruding conical surface with an angle of about 2' between the base plane and the surface of the cone as a sequence of the optical thickness gradient toward the centre in the spiral arm regions.

We are trying to probe conditions in the youngest super star clusters, those still embedded in dense obscuring clouds. The hydrogen recombination lines in the radio and infrared can be observed through the obscuration, as the optical and UV lines cannot, and give us the kinematics of the ionized gas. The line profiles of the clusters resemble superpositions of the lines of many very young ultra-compact or hyper-compact HII regions. This can be explained if each OB star is individually embedded in dense material which it is accreting, even as it ionizes. We speculate on what this implies for conditions in the clusters.

Here, we report on the first results from the e-MERLIN Cyg OB2 Radio Survey (COBRaS), which is designed to exploit e-MERLIN’s enhanced capabilities to conduct deep-field mapping of the tremendously rich Cyg OB2 association. The project aims to deliver the most detailed radio census of the most massive OB association in the northern hemisphere. There exists considerable evidence for clumping in the winds of hot stars, which has hugely important consequences for mass-loss determinations. The amount of mass lost from a massive star is a crucial parameter required for stellar and cluster evolution models that are paramount to our understanding of the formation and evolution of massive star clusters. Presenting some of the first 20cm (L band) detections of massive stars in Cyg OB2, both accurate mass-loss determinations and constraints upon clumping within their winds are made. These data substantially increase the observational detections of the outer wind of massive stars and in combination with other observations at different wavelengths, COBRaS will greatly advance our knowledge of clumping as a function of radial distance around massive stars.

We show that in many methanol maser sources the masers are located in lines, with a velocity gradient along them which suggests that the masers are situated in edge-on circumstellar, or protoplanetary, disks. We present VLBI observations of the methanol maser source G309.92+0.48, in the 12.2 GHz transition, which confirm previous observations that the masers in this source lie along a line. We show that such sources are not only linear in space but, in many cases, also have a linear velocity gradient. We then model these and other data in both the 6.7 GHz and the 12.2 GHz transition from a number of star formation regions, and show that the observed spatial and velocity distribution of methanol masers, and the derived Keplerian masses, are consistent with a circumstellar disk rotating around an OB star. We consider this and other hypotheses, and conclude that about half of these methanol masers are probably located in edge-on circumstellar disks around young stars. This is of particular significance for studies of circumstellar disks because of the detailed velocity information available from the masers., 38 pages, 13 figures accepted by ApJ

We examine the spectral characteristics of normal OB stars with high–signal-to-noise ratio (>120) H-band (1.6 μm) spectra at a resolution of 2000. We find that several atomic lines vary smoothly with stellar temperature, as first shown by Blum et al. However, we find a previously unreported, significant variation in the strength of some of these lines with stellar luminosity. B supergiant stars show stronger He I and weaker Br 11 as compared with low-luminosity B dwarf stars of the same spectral class. It is for this reason that luminosity class must also be determined to obtain an accurate spectral type for a given star using H-band spectra. We suggest a method for estimating the spectral type and luminosity of an OB star over the wavelength range from 1.66 to 1.72 μm using hydrogen Br 11 at 1.681 μm, He I at 1.700 μm, and He II at 1.693 μm. The use of the near-infrared spectral range for classification has obvious advantages over optical classification when applied to heavily reddened stars, such as in star-forming regions or deeply embedded lines of sight within the plane of the Galaxy, such as the Galactic center. Furthermore, the H band is less likely to be contaminated by infrared excess emission, which is frequently seen around massive young stellar objects beyond 2 μm.

We use Monte Carlo methods to simulate the properties of a Galactic population of rotation-powered pulsars in the self-consistent outer gap model proposed by Zhang & Cheng, where the initial magnetic field and spatial and velocity distributions of the neutron stars at birth are obtained from the statistical results of radio pulsars. We obtain the distance, period, age, magnetic field, and γ-ray flux distributions of the γ-ray pulsars whose γ-ray and radio fluxes are above the detectable threshold fluxes. Furthermore, we simulate the properties of Geminga-like pulsars and obtain the possible parametric region and the number of the Geminga-like pulsars. In our simulations, the different beaming effects of radio and γ-ray beams are taken into account. We predict that there may be ~11 γ-ray pulsars that are detectable at both radio and γ-ray energies and ~37 Geminga-like pulsars in the Galactic plane (| b | < 5°) if the γ-ray beaming fraction is 0.67 and the birthrate of the neutron stars is 1 per century. Compared to the flux distribution, individual spectrum, and distance distribution obtained by assuming OB star associations of our simulated Geminga-like pulsars and the unidentified EGRET sources at | b | < 5°, we conclude that the majority of the unidentified γ-ray point sources near the Galactic plane may be Geminga-like pulsars. We also suggest that the most possible radio pulsars likely to be confirmed as γ-ray pulsars in future are those with LX/Ėsd ~10−3.

New spectroscopic observations of three O+O binary stars (LZ Cep, SZ Cam and IU Aur), obtained over a number of years at the Dominion Astrophysical Observatory, are analysed using state-of-the-art cross-correlation techniques to produce radial velocity curves. These results are combined with new (LZ Cep) and published (SZ Cam and IU Aur) photometry to yield masses, temperatures, radii and luminosities. We find that LZ Cep is a semi-detached system, in agreement with the results of Howarth et al., with the secondary star filling its Roche lobe. We find a distance modulus of 9.6 ?‚?? 0.2, which is slightly smaller than the distance modulus to Cep OB2 (= 9.9).The reddening of LZ Cep is also at the lower end of the cluster range, suggesting that the binary is located on the near side of the cluster. SZ Cam is a triple system, and we are able to measure the radial velocities of the three components that are observed in the absorption lines. A light-curve solution employing our new mass ratio shows that the short-period binary is detached. The third body emits about 40 per cent of the radiation from the system, and is probably a binary itself. The distance modulus for SZ Cam (= 9.88) is in good agreement with that of its parent cluster NGC 1502 (= 9.71). IU Aur is another triple system, although we are unable to find spectroscopic evidence for the tertiary. The close binary is semi-detached, with the secondary filling its Roche lobe. The distance modulus of the system is 11.0, which is in approximate agreement with that of the Aur OB1 association (= 10.6 ?‚?? 0.2). We note that the current models for interacting massive binaries all assume case B mass transfer, in which the mass-loser becomes a Wolf–Rayet star. Case A mass-transfer models (in which the mass-loser fills its Roche lobe while still on the main sequence) are required in order to see whether or not they can explain the observed properties of these interacting systems.

We have obtained a high-quality ASCA spectrum of the MK standard B0 V star τ Sco in order to test the standard wind-shock picture of OB star X-ray production. The fluxes in three line complexes from ions indicative of hot plasma—Mg+10, Si+12, and S+14—are measured, and we also present a global spectral fit using a fairly standard multitemperature, optically thin, collisional equilibrium model. We were able to achieve a statistically good fit, but only by using the MeKaL plasma emission code (Mewe, Kaastra, & Liedahl) and fixing the elemental abundances at the photospheric values as determined by optical spectroscopy. The parameters of the model are T1 = 7 MK, EM1 = 3.5 × 1054 cm-3, T2 = 12 MK, EM2 = 8.1 × 1053 cm-3, T3 > 27 MK, EM3 > 3.0 × 1053 cm-3. The quantity of material with temperature in excess of 107 K on τ Sco is comparable to that with temperature in excess of 106 K on most other early B stars. The data cannot be explained by the standard line-force instability wind-shock mechanism. However, more unusual shock mechanisms involving magnetically confined wind shocks or interactions between infalling matter and the ambient stellar wind cannot be ruled out. Alternately, a dynamo driven by differential rotation could be powering coronal plasma. If magnetic fields are involved in any way, then the star's extreme youth could play a role.

A long-term spectroscopic and photometric survey of the most luminous and massive stars in the vicinity of the super-massive black hole Sgr A* revealed two new binaries; a long-period Ofpe/WN9 binary, GCIRS 16NE, with a modest eccentricity of 0.3 and a period of 224 days and an eclipsing Wolf-Rayet binary with a period of 2.3 days. Together with the already identified binary GCIRS 16SW, there are now three confirmed OB/WR binaries in the inner 0.2\,pc of the Galactic Center. Using radial velocity change upper limits, we were able to constrain the spectroscopic binary fraction in the Galactic Center to $F_{\rm SB}=0.27^{+0.29}_{-0.19}$ at a confidence level of 95%, a massive binary fraction similar to that observed in dense clusters. The fraction of eclipsing binaries with photometric amplitudes $\Delta m>0.4$ is $F^{\rm GC}_{\rm EB}=3\pm2%$, which is consistent with local OB star clusters ($F_{\rm EB}=1%$). Overall the Galactic Center binary fraction seems to be close to the binary fraction in comparable young clusters., Comment: 5 figures, submitted to ApJ

BRITE-Constellation (where BRITE stands for BRIght Target Explorer) is an international nanosatellite mission to monitor photometrically, in two colours, brightness and temperature variations of stars brighter than V = 4. The current mission design consists of three pairs of 7 kg nanosats from Austria, Canada and Poland carrying optical telescopes and CCDs. One instrument in each pair is equipped with a blue filter; the other, a red filter. The first two nanosats are UNIBRITE, designed and built by University of Toronto Institute for Aerospace Studies - Space Flight Laboratory and its twin, BRITE-Austria, built by the Technical University Graz with support of UTIAS-SFL. They were launched on 25 February 2013 by the Indian Space Agency under contract to the Canadian Space Agency into a low-Earth dusk-dawn polar orbit., Comment: 2 page abstract of a full paper to be submitted

Our star-count analysis of the Two Micron All Sky Survey point sources resulted in an identification of the star cluster G144.9+0.4. The cluster was found, but not characterized, by Glushkova et al. We show that the cluster is physically associated with the Cam OB1 association at a distance of about 1 kpc and with an age of 1-2 Myr. Pre-main sequence stars are identified on the basis of photometric and proper motion data. A total of 91 additional OB star candidates was found in subgroups 1A and 1B, a significant increase from the currently known 43 OB stars. The OB members show an age spread that indicates a sustained star formation for at least the last 10-15 Myr. The young cluster G144.9+0.4 represents the latest episode of sequential star formation in this cloud complex., Comment: 33pages, 10 figures, published in ApJ

The Rosette complex is a well studied region of the galactic plane which presents the apparent characteristics of a triggered star forming region. This is however still debated as no strong evidence corroborates this statement. We focus on characterizing the young stellar population in the Rosette complex to improve our understanding of the processes that regulate the star formation in this region. We propose an original method that relies on the joint analysis of the star color and density in the near-infrared. It leads to mapping the molecular cloud spatial distribution and detecting the embedded clusters with their characterization in terms of member number and age estimation. We have identified 13 clusters, 2 of which are new discoveries, and we estimate that the total number of young stellar objects in the Rosette ranges between 4000 and 8000 members. We find that the age distribution of the young clusters is not consistent with a general triggered scenario for the star formation in this molecular cloud. This study proves that the Rosette complex evolution is not governed by the influence of its OB star population. It suggests that the simple morphological appearance of an active region is not sufficient to conclude much about the triggering role in the star formation process. Our method of constraining the cluster properties using UKIDSS and WISE data has proven efficient, and studies of other regions of the galactic plane would definitely benefit from this approach., Comment: Accepted for publication in A&A. 11 pages, 10 figures. Language edited version

MYStIX (Massive Young Star-Forming Complex Study in Infrared and Xray) seeks to characterize 20 OB-dominated young clusters and their environs at distances d < 4 kpc using imaging detectors on the Chandra X-ray Observatory, Spitzer Space Telescope, and the United Kingdom InfraRed Telescope. The observational goals are to construct catalogs of star-forming complex stellar members with well-defined criteria, and maps of nebular gas (particularly of hot X-ray emitting plasma) and dust. A catalog of MYStIX Probable Complex Members (MPCMs) with several hundred OB stars and > 30, 000 low mass premain sequence is assembled. This sample and related data products will be used to seek new empirical constraints on theoretical models of cluster formation and dynamics, mass segregation, OB star formation, star formation triggering on the periphery of HII regions, the survivability of protoplanetary disks in HII regions. This paper give an introduction and overview of the project, covering the data analysis methodology and application to two star forming regions, NGC 2264 and the Trifid Nebula., 74 pages, 10 figures. To appear in Astrophysical Journal Supplements (with 6 other MYStIX papers). A version with complete figures is available at http://www.astro.psu.edu/mystix

We present the results of optical spectroscopic follow-up of 125 candidate main sequence OB stars in the Small Magellanic Cloud (SMC) that were originally identified in the S3MC infrared imaging survey as showing an excess of emission at 24 um indicative of warm dust, such as that associated with a transitional or debris disks. We use these long-slit spectra to investigate the origin of the 24 um emission and the nature of these stars. A possible explanation for the observed 24 um excess, that these are emission line stars with dusty excretion disks, is disproven for the majority of our sources. We find that 88 of these objects are normal stars without line emission, with spectral types mostly ranging from late-O to early-B; luminosity classes a sub-set of our sample indicate that most are main-sequence stars. We further identify 17 emission-line stars, 7 possible emission-line stars, and 5 other stars with forbidden-line emission. We discover a new O6 Iaf star; it exhibits strong HeII 4686 A emission but relatively weak NIII 4640 A emission that we attribute to the lower nitrogen abundance in the SMC. Two other objects are identified with planetary nebulae, one with a young stellar object, and two with X-ray binaries. To shed additional light on the nature of the observed 24 um excess we use optical and infrared photometry to estimate the dust properties of the objects with normal O and B star spectra and compare these properties to those of a sample of hot spots in the Galactic interstellar medium (ISM). We find that the dust properties of the dusty OB star sample resemble the properties of the Galactic sample of hot spots. Some may be runaway systems with bow-shocks resulting from a large velocity difference between star and ISM. We further investigate the nature of these dusty OB stars in a companion paper presenting mid-infrared spectroscopy and additional imaging., Comment: Accepted for publication in ApJ; 38 pages, 18 figures, 7 tables

We report the discovery of a14NH3 maser in the (J, K) = (3, 3) transition toward the W51-North H II complex. The maser line has a FWHM of 1.7 km s-1 and an asymmetric profile, which suggests multiple features in the velocity range. Measured with the VLA, the maser emission has a peak flux of 230 mJy and a maximum deconvolved size of 02. These values set a lower limit to the brightness temperature of 1.3 ? 104 K. Thermal emission of ammonia was also detected toward this region. The elongated structure, velocity, and temperature gradients, and high excitation of the thermal ammonia indicate that the (3, 3) maser is excited in an expanding shell of a molecular outflow, powered possibly by the massive OB star D2. Molecular hydrogen densities and kinetic temperatures in the maser region are consistent with models of collisional pumping of the (3, 3) maser.

Filamentary structures are ubiquitously seen in the interstellar medium. The concentrated molecular mass in the filaments allows fragmentation to occur in a shorter timescale than the timescale of the global collapse. Such hierarchical fragmentation may further assist the dissipation of excessive angular momentum. It is crucial to resolve the morphology and the internal velocity structures of the molecular filaments observationally. We perform 0".5-2".5 angular resolution interferometric observations toward the nearly face-on OB cluster forming region G33.92+0.11. Observations of various spectral lines as well as the millimeter dust continuum emission, consistently trace several $\sim$1 pc scale, clumpy molecular arms. Some of the molecular arms geometrically merge to an inner 3.0$^{{\scriptsize{+2.8}}}_{{-\scriptsize{1.4}}}\cdot10^{3}$\,$M_{\odot}$, 0.6 pc scale central molecular clump, and may directly channel the molecular gas to the warm ($\sim$50 K) molecular gas immediately surrounding the centrally embedded OB stars. The NH$_{3}$ spectra suggest a medium turbulence line width of FWHM$\lesssim$2\,km\,s$^{-1}$ in the central molecular clump, implying a $\gtrsim$10 times larger molecular mass than the virial mass. Feedbacks from shocks and the centrally embedded OB stars and localized (proto)stellar clusters, likely play a key role in the heating of molecular gas and could lead to the observed chemical stratification. Although (proto)stellar feedbacks are already present, G33.92+0.11 chemically appears to be at an early evolutionary stage given by the low abundance limit of SO$_{2}$ observed in this region., Comment: 37 pages, 23 figures

Some theories of star formation suggest massive stars may only form in clustered environments, which would create a deficit of massive stars in low density environments. Observationally, Massey (2002) finds such a deficit in samples of the field population in the Small and Large Magellanic Clouds, with an IMF slope of {\Gamma} ~ 4. These IMF measurements represent some of the largest known deviations from the standard Salpeter IMF slope of {\Gamma}=1.35. Here, we carry out a comprehensive investigation of the mass function above 20 solar masses for the entire field population of the Small Magellanic Cloud, based on data from the Runaways and Isolated O Type Star Spectroscopic Survey of the SMC (RIOTS4). This is a spatially complete census of the entire field OB star population of the SMC obtained with the IMACS multi-object spectrograph and MIKE echelle spectrograph on the Magellan telescopes. Based on Monte-Carlo simulations of the evolved present-day mass function, we find the slope of the field IMF above 20 solar masses is {\Gamma}=2.3+/-0.4. We extend our IMF measurement to lower masses using BV photometry from the OGLE II survey. We use a statistical approach to generate a probability distribution for the mass of each star from the OGLE photometry, and we again find {\Gamma}=2.3+/-0.6 for stellar masses from 7-20 solar masses. The discovery and removal of ten runaways in our RIOTS4 sample steepens the field IMF slope to {\Gamma}=2.8+/-0.5. We discuss the possible effects of binarity and star-formation history on our results, and conclude that the steep field massive star IMF is most likely a real effect., Comment: 19 pages, 15 figures, Accepted for publication in ApJ

Using the results of observations of the Carina nebula made with the space telescope Glazar, it is shown that the extinction law for the nebula is abnormal and that there is a single OB star complex within the nebula at a distance of about 2200 pc. It is suggested that the observed distribution of OB stars in the nebula and also the appearance of the nebula itself is due to a specific structure of the absorbing clouds within the nebula, and that the absorbing clouds may have such structure as a result of an explosion in the center of the nebula.

X-ray observations of the double-binary OB-star system QZ Car (HD 93206) obtained with the Chandra X-ray Observatory over a period of roughly 2 years are presented. The orbit of systems A (O9.7 I+b2 v, PA = 21 d) and B (O8 III+o9 v, PB = 6 d) are reasonably well sampled by the observations, allowing the origin of the X-ray emission to be examined in detail. The X-ray spectra can be well fitted by an attenuated three temperature thermal plasma model, characterised by cool, moderate, and hot plasma components at kT ~ 0.2, 0.7, and 2 keV, respectively, and a circumstellar absorption of ~ 0.2 x 10^22 cm-2. Although the hot plasma component could be indicating the presence of wind-wind collision shocks in the system, the model fluxes calculated from spectral fits, with an average value of ~ 7 x 10^-13 erg s-1 cm-2, do not show a clear correlation with the orbits of the two constituent binaries. A semi-analytical model of QZ Car reveals that a stable momentum balance may not be established in either system A or B. Yet, despite this, system B is expected to produce an observed X-ray flux well in excess of the observations. If one considers the wind of the O8 III star to be disrupted by mass transfer the model and observations are in far better agreement, which lends support to the previous suggestion of mass-transfer in the O8 III + o9 v binary. We conclude that the X-ray emission from QZ Car can be reasonably well accounted for by a combination of contributions mainly from the single stars and the mutual wind-wind collision between systems A and B., 11 pages, 7 figures. Accepted for the ApJS Special Issue on the Chandra Carina Complex Project (CCCP), scheduled for publication in May 2011. All 16 CCCP Special Issue papers are available at http://cochise.astro.psu.edu/Carina_public/special_issue.html through 2011 at least

The excitation mechanisms behind the slow pulsations―with periods of the order of one day―of OB stars are discussed on the basis of numerical computations. Non-radial, non-adiabatic stability analysis is performed on a set of evolutionary models with masses between 5.2 M ○ . and 12.1 M ○ .. The long-period oscillations in stellar models below the newly recovered β Cephei region are found to be excited by the iron bump in the newly available OPAL opacities. For more massive stars exhibiting oscillations with periods of the order of one day, however, another excitation mechanism must be sought

There is much debate on how high-mass star formation varies with environment, and whether the sparsest star-forming environments are capable of forming massive stars. To address this issue, we have observed eight apparently isolated OB stars in the SMC using HST's Advanced Camera for Surveys. Five of these objects appear as isolated stars, two of which are confirmed to be runaways. The remaining three objects are found to exist in sparse clusters, with 20 solar mass and N_*,lo >40 match best with observations of SMC and Galactic OB star populations. We examine the mass ratio of the second-most massive and most massive stars (m_max,2/m_max), finding that our observations all exist below the 20th percentile of our simulated clusters. However, all of our observed clusters lie within the parameter space spanned by the simulated clusters, although some are in the lowest 5th percentile frequency. These results suggest that clusters are built stochastically by randomly sampling stars from a universal IMF with a fixed stellar upper-mass limit. In particular, we see no evidence to suggest a m_max - M_cl relation. Our results may be more consistent with core accretion models of star formation than with competitive accretion models, and they are inconsistent with the proposed steepening of the integrated galaxy IMF (IGIMF)., 19 pages, 12 figures, accepted for publication in ApJ

We present the results from new Nobeyama Millimeter Array observations of CO(1-0), HCN(1-0), and 89-GHz continuum emissions toward NGC 604, known as the supergiant H ii region in a nearby galaxy M 33. Our high spatial resolution images of CO emission allowed us to uncover ten individual molecular clouds that have masses of (0.8 -7.4) 10$^5$M$_{\sun }$ and sizes of 5 -- 29 pc, comparable to those of typical Galactic giant molecular clouds (GMCs). Moreover, we detected for the first time HCN emission in the two most massive clouds and 89 GHz continuum emission at the rims of the "H${\alpha}$ shells". Three out of ten CO clouds are well correlated with the H${\alpha}$ shells both in spatial and velocity domains, implying an interaction between molecular gas and the expanding H ii region. Furthermore, we estimated star formation efficiencies (SFEs) for each cloud from the 89-GHz and combination of H${\alpha}$ and 24-${\mu}$m data, and found that the SFEs decrease with increasing projected distance measured from the heart of the central OB star cluster in NGC 604, suggesting the radial changes in evolutionary stages of the molecular clouds in course of stellar cluster formation. Our results provide further support to the picture of sequential star formation in NGC604 initially proposed by Tosaki et al. (2007) with the higher spatially resolved molecular clouds, in which an isotropic expansion of the H ii region pushes gases outward and accumulates them to consecutively form dense molecular clouds, and then induces massive star formations., Comment: 23 pages, 8 figures, accepted for publication in ApJ

The very young open cluster NGC 6383 centered on the O-star binary HD 159176 is an interesting place for studying the impact of early-type stars with strong radiation fields and powerful winds on the formation processes of low-mass stars. To investigate this process, it is necessary to determine the characteristics (age, presence, or absence of circumstellar material) of the population of low-mass pre-main-sequence (PMS) stars in the cluster. We obtained deep U B V (R I)_c H-alpha photometric data of the entire cluster as well as medium-resolution optical spectroscopy of a subsample of X-ray selected objects. Our spectroscopic data reveal only very weak H-alpha emission lines in a few X-ray selected PMS candidates. We photometrically identify a number of H-alpha emission candidates but their cluster membership is uncertain. We find that the fainter objects in the field of view have a wide range of extinction (up to A_V = 20), one X-ray selected OB star having A_V ~ 8. Our investigation uncovers a population of PMS stars in NGC 6383 that are probably coeval with HD 159176. In addition, we detect a population of reddened objects that are probably located at different depths within the natal molecular cloud of the cluster. Finally, we identify a rather complex spatial distribution of H-alpha emitters, which is probably indicative of a severe contamination by foreground and background stars., Comment: Accepted for publication in Astronomy & Astrophysics

Some statistical studies on the nearby early-type stars proposed for observations by HIPPARCOS are presented. Results on spatial orientation and kinematics are in agreement with those found in the literature. An age estimate based on non-kinematical hypothesis is found to be somewhat smaller than expansion ages derives by some authors.

In this paper we have carried out an analysis of the predictions of the radiatively driven stellar winds theories on 63 stars belonging to clusters or associations. The spectral types in our sample range from O3 to B0 and all classes of luminosity are considered. The study has been carried out starting from the relationship between the stellar-wind velocity (v edge) obtained from the resonance doublet ofCIV for stars observed with the IUE, and the escape velocity. The stellar masses have been obtained from the evolutionary tracks of Maeder and Meynet. Results from recent NLTE analyses with blanketing of lines and winds have been used for the effective temperature.

We have studied the interstellar column densities of Alii, Siii,Sii, Feii, Niii, and Znii in the direction of 18 O- and 6 B-type stars so as to improve the relations of element depletions withE(B-V), and to look for other possible relations with two stellar parameters: namely, the rate of mass loss and rotational velocity. The stars were chosen in order to cover several directions in the Galaxy, as well as a wide range in interstellar reddening. We found a clear inverse trend relating the abundance of elements to interstellar reddening.

The remarkable astrometric capabilities of Chandra offer the possibility to measure proper motions of X-ray sources with an unprecedented accuracy in this wavelength range. We recently completed a proper motion survey of three of the seven thermally emitting radio-quiet isolated neutron stars (INSs) discovered in the ROSAT all-sky survey. These INSs (RX J0420.0-5022, RX J0806.4-4123, and RX J1308.6+2127) either lack an optical counterpart or have one so faint that ground based or space born optical observations push the current possibilities of the instrumentation to the limit. Pairs of ACIS observations were acquired 3 to 5 years apart to measure the displacement of the sources on the X-ray sky using as reference the background of extragalactic or remote Galactic X-ray sources. We derive 2 sigma upper limits of 123 mas/yr and 86 mas/yr on the proper motion of RX J0420.0-5022 and RX J0806.4-4123, respectively. RX J1308.6+2127 exhibits a very significant displacement (~ 9 sigma) yielding mu = 220 +/- 25 mas/yr, the second fastest measured among all ROSAT discovered INSs. The source is probably moving away rapidly from the Galactic plane at a speed which precludes any significant accretion of matter from the interstellar medium. Its transverse velocity of ~ 740 (d/700pc) km/s might be the largest of all ROSAT INSs and its corresponding spatial velocity stands among the fastest recorded for neutron stars. RX J1308.6+2127 is thus a middle-aged (age ~ 1 My) high velocity cooling neutron star. We investigate its possible origin in nearby OB associations or from a field OB star. In most cases, the flight time from birth place appears significantly shorter than the characteristic age derived from spin down rate. The distribution in transverse velocity of ROSAT INSs is not statistically different from that of normal radio pulsars., 14 pages, 5 figures, accepted for publication in A&A

Context. Comparison of optical/uv absorption line data with high-resolution profiles of mm-wave CO emission provides complementary information on the absorbing gas, as toward ζOph. Over the past thirty years a wealth of observations of CO and other molecules in optical/uv absorption in diffuse clouds has accumulated for which no comparable CO emission line data exist. Aims. To acquire mm-wave J = 1-0 CO emission line profiles toward a substantial sample of commonly-studied optical/uv absorption line targets and to compare with the properties of the absorbing gas, especially the predicted emission line strengths. Methods. Using the ARO 12 m telescope, we observed mm-wavelength J = 1-0 CO emission with spectral resolution R ≈ 3 x 10 6 and spatial resolution 1' toward a sample of 110 lines of sight previously studied in optical/uv absorption lines of CO, H 2 , CH, etc. Results. Interstellar CO emission was detected along 65 of the 110 lines of sight surveyed and there is a general superabundance of CO emission given the distribution of galactic latitudes in the survey sample. Much of the emission is optically thick or very intense and must emanate from dark clouds or warm dense gas near HII regions. Conclusions. Judging from the statistical superabundance of CO emission, seen also in the total line of sight reddening, the OB star optical/uv absorption line targets must be physically associated with the large quantities of neutral gas whose CO emission was detected, in which case they are probably influencing the absorbing gas by heating and/or photoionizing it. This explains why CO/H 2 and 12 CO/ 13 CO ratios differ somewhat between uv and mm-wave absorption line studies. Because the lines of sight have been preselected to have Av ≤ 1 mag, relatively little of the associated material actually occults the targets, making it difficult for CO emission line observations to isolate the foreground gas contribution.

By comparing mass loss rates determined from radio, Hα, and UV resonance lines, it is now reasonably certain that clumping in OB star winds affects empirical determinations of their mass loss rates. We examine three UV wind line diagnostics that are sensitive to clumping and, ultimately, may help constrain its nature. They are: 1) Doublet ratios of resonance lines. 2) Ratio of the resonance and radiatively excited state lines. 3) Narrow absorption components near the terminal velocity in stars with weak winds.