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Register a new userThe distances of 61 PGCCs in the Second Galactic Quadrant
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Determining the distances to the Planck Galactic cold clumps (PGCCs) is crucial for the measurement of their physical parameters and the study of their Galactic distribution. Based on two large catalogues of stars with robust distances and reddening estimates from the literature, we have estimated accurate distances to 61 PGCCs in the second Galactic quadrant. For this purpose, we have selected stars along the sightlines overlapping with the cores of the sample clumps and fitted the reddening profiles with a simple reddening model. The typical uncertainties of the resultant distances of these PGCCs are less than 8 per cent. The new estimates differ significantly from the kinematic values, well known to suffer from large errors. With the new distances, we have updated the physical properties including the radii, masses and virial parameters of the cores of the PGCCs.
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In order to understand the initial conditions and early evolution of star formation in a wide range of Galactic environments, we carried out an investigation of 64 textit{Planck} Galactic Cold Clumps (PGCCs) in the second quadrant of the Milky Way. Using the $^{13}$CO and C$^{18}$O $J = 1 - 0$ lines, and 850,$mu$m continuum observations, we investigated cloud fragmentation and evolution associated with star formation. We extracted 468 clumps and 117 cores from the $^{13}$CO line and 850,$mu$m continuum maps, respectively. We make use of the Bayesian Distance Calculator and derived the distances of all 64 PGCCs. We found that in general, the mass-size plane follows a relation of $msim r^{1.67}$. At a given scale, the masses of our objects are around 1/10 of that of typical Galactic massive star-forming regions. Analysis of the clump and core masses, virial parameters, densities, and mass-size relation suggests that the PGCCs in our sample have a low core formation efficiency ($sim$3.0%), and most PGCCs are likely low-mass star-forming candidates. Statistical study indicates that the 850,$mu$m cores are more turbulent, more optically thick, and denser than the $^{13}$CO clumps for star formation candidates, suggesting that the 850,$mu$m cores are likely more appropriate future star-formation candidates than the $^{13}$CO clumps.
Distance measurements to molecular clouds are essential and important. We present directly measured distances to 169 molecular clouds in the fourth quadrant of the Milky Way. Based on the near-infrared photometry from the Two Micron All Sky Survey and the Vista Variables in the Via Lactea Survey, we select red clump stars in the overlapping directions of the individual molecular clouds and infer the bin averaged extinction values and distances to these stars. We track the extinction versus distance profiles of the sightlines toward the clouds and fit them with Gaussian dust distribution models to find the distances to the clouds. We have obtained distances to 169 molecular clouds selected from Rice et al. The clouds range in distances between 2 and 11 kpc from the Sun. The typical internal uncertainties in the distances are less than 5 per cent and the systematic uncertainty is about 7 per cent. The catalogue presented in this work is one of the largest homogeneous catalogues of distant molecular clouds with the direct measurement of distances. Based on the catalogue, we have tested different spiral arm models from the literature.
Filamentary structures are common morphological features of the cold, molecular interstellar medium (ISM). Recent studies have discovered massive, hundred-parsec-scale filaments that may be connected to the large-scale, Galactic spiral arm structure. Addressing the nature of these Giant Molecular Filaments (GMFs) requires a census of their occurrence and properties. We perform a systematic search of GMFs in the fourth Galactic quadrant and determine their basic physical properties. We identify GMFs based on their dust extinction signatures in near- and mid-infrared and velocity structure probed by ^{13}CO line emission. We use the ^{13}CO line emission and ATLASGAL dust emission data to estimate the total and dense gas masses of the GMFs. We combine our sample with an earlier sample from literature and study the Galactic environment of the GMFs. We identify nine GMFs in the fourth Galactic quadrant; six are located in the Centaurus spiral arm and three in inter-arm regions. Combining this sample with an earlier study using the same identification criteria in the first Galactic quadrant results in 16 GMFs, nine of which are located within spiral arms. The GMFs have sizes of 80-160 pc and ^{13}CO-derived masses between 5-90 x 10^{4} Msun. Their dense gas mass fractions are between 1.5-37%, being higher in the GMFs connected to spiral arms. We also compare the different GMF-identification methods and find that emission and extinction based techniques overlap only partially, highlighting the need to use both to achieve a complete census.
We analyse the poorly-studied open cluster King~1 in the second Galactic quadrant. From wide-field photometry we have studied the spatial distribution of this cluster. We determined that the centre of King~1 is located at $alpha_{2000}=00^{rm h}22^{rm m}$ and $delta_{2000}=+64degr23arcmin$. By parameterizing the stellar density with a King profile we have obtained a central density of $rho_{0}=6.5pm0.2$ star arcmin$^{-2}$ and a core radius of $r_{rm core}=1farcm9pm0farcm2$. By comparing the observed color-magnitude diagram of King~1 with those of similar open clusters and with different sets of isochrones, we have estimated an age of $2.8pm0.3$ Gyr, a distance modulus of $(m-M)_{rm o}=10.6pm0.1$ mag, and a reddening of $E(B-V)=0.80pm0.05$ mag. To complete our analysis we acquired medium resolution spectra for 189 stars in the area of King~1. From their derived radial velocities we determined an average velocity $leftlangle V_rrightrangle $=-53.1$pm$3.1 km s$^{-1}$. From the strength of the infrared mbox{Ca,{sc ii}} lines in red giants we have determined an average metallicity of $leftlangle [M/H]rightrangle$=+0.07$pm$0.08 dex. From spectral synthesis we have also estimated an $alpha$-elements abundance of $leftlangle [alpha/M]rightrangle$=-0.10$pm$0.08 dex.
We report H$alpha$ filter photometry for 197 northern hemisphere planetary nebulae (PNe) obtained using imaging data from the IPHAS survey. H$alpha$+[N II] fluxes were measured for 46 confirmed or possible PNe discovered by the IPHAS survey and for 151 previously catalogued PNe that fell within the area of the northern Galactic Plane surveyed by IPHAS. After correcting for [N II] emission admitted by the IPHAS H$alpha$ filter, the resulting H$alpha$ fluxes were combined with published radio free-free fluxes and H$beta$ fluxes, in order to estimate mean optical extinctions to 143 PNe using ratios involving their integrated Balmer line fluxes and their extinction-free radio fluxes. Distances to the PNe were then estimated using three different 3D interstellar dust extinction mapping methods, including the IPHAS-based H-MEAD algorithm of Sale (2014). These methods were used to plot dust extinction versus distance relationships for the lines of sight to the PNe; the intercepts with the derived dust optical extinctions allowed distances to the PNe to be inferred. For 17 of the PNe in our sample reliable Gaia DR2 distances were available and these have been compared with the distances derived using three different extinction mapping algorithms as well as with distances from the nebular radius vs. H$alpha$ surface brightness relation of Frew et al. (2016). That relation and the H-MEAD extinction mapping algorithm yielded the closest agreement with the Gaia DR2 distances.
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