- ID:
- ivo://CDS.VizieR/J/A+A/600/A2
- Title:
- Hydrogen in diffuse molecular clouds
- Short Name:
- J/A+A/600/A2
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Recent sub-millimeter and far-infrared wavelength observations of absorption in the rotational ground state lines of various simple molecules against distant Galactic continuum sources have opened the possibility to study the chemistry of diffuse molecular clouds Milky Way-wide. In order to calculate abundances the column densities of molecular and atomic hydrogen, HI, must be known. We aim at determining the atomic hydrogen column densities for diffuse clouds located on the sight lines toward a sample of prominent high mass star forming regions that were intensely studied with the HIFI instrument onboard Herschel. Based on Jansky Very Large Array data, we employ the 21-cm HI absorption-line technique to construct profiles of the HI opacity versus radial velocity toward our target sources. These profiles are combined with lower resolution archival data of extended HI emission to calculate the HI column densities of the individual clouds along the sight lines. We employ Bayesian inference to estimate the uncertainties of the derived quantities. Our study delivers reliable estimates of the atomic hydrogen column density for a large number of diffuse molecular clouds at various Galactocentric distances. Together with column densities of molecular hydrogen derived from its surrogates observed with HIFI, the measurements can be used to characterize the clouds and, e.g., investigate the dependence of their chemistry on the molecular fraction.
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292. IC 4665 DANCe
- ID:
- ivo://CDS.VizieR/J/A+A/631/A57
- Title:
- IC 4665 DANCe
- Short Name:
- J/A+A/631/A57
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The study of star formation is extremely challenging due to the lack of complete and clean samples of young, nearby clusters, and star forming regions. The recent Gaia DR2 catalogue complemented with the deep, ground based COSMIC DANCe catalogue offers a new database of unprecedented accuracy to revisit the membership of clusters and star forming regions. The 30 Myr open cluster IC 4665 is one of the few well-known clusters of this age and it is an excellent target where to test evolutionary models and study planetary formation. We aim to provide a comprehensive membership analysis of IC 4665 and to study the following properties: empirical isochrones, distance, magnitude distribution, present-day system mass function, and spatial distribution. We use the Gaia DR2 catalogue together with the DANCe catalogue to look for members using a probabilistic model of the distribution of the observable quantities in both the cluster and background populations. We obtain a final list of 819 candidate members which cover a 12.4 magnitude range (7<J<19.4). We find that 50% are new candidates, and we estimate a conservative contamination rate of 20%. This unique sample of members allows us to obtain a present-day system mass function in the range of 0.02-6M_{sun}_, which reveals a number of details not seen in previous studies. In addition, they favour a spherically symmetric spatial distribution for this young open cluster. Our membership analysis represents a significant increase in the quantity and quality (low-contamination) with respect to previous studies. As such, it offers an excellent opportunity to revisit other fundamental parameters such as the age.
- ID:
- ivo://CDS.VizieR/V/165
- Title:
- IGAPS. merged IPHAS and UVEX of northern Galactic plane
- Short Name:
- V/165
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The INT Galactic Plane Survey (IGAPS) is the merger of the optical photometric surveys, IPHAS and UVEX, based on data from the Isaac Newton Telescope (INT) obtained between 2003 and 2018. Here, we present the IGAPS point source catalogue. It contains 295.4 million rows providing photometry in the filters, i, r, narrow-band H{alpha}, g, and URGO. The IGAPS footprint fills the Galactic coordinate range, |b|<5{deg} and 30{deg}<l<215{deg}. A uniform calibration, referred to as the Pan-STARRS system, is applied to g, r, and i, while the H{alpha} calibration is linked to r and then is reconciled via field overlaps. The astrometry in all five bands has been recalculated in the reference frame of Gaia Data Release 2. Down to i~20mag (Vega system), most stars are also detected in g, r, and H{alpha}. As exposures in the r band were obtained in both the IPHAS and UVEX surveys, typically a few years apart, the catalogue includes two distinct r measures, r_I_ and r_U_. The r 10{sigma} limiting magnitude is approximately 21, with median seeing of 1.1arcsec. Between approximately 13^th^ and 19^th^ mag in all bands, the photometry is internally reproducible to within 0.02 magnitudes. Stars brighter than r=19.5mag are tested for narrow-band H{alpha} excess signalling line emission, and for variation exceeding |r_I_-r_U_|=0.2mag. We find and flag 8292 candidate emission line stars and over 53000 variables (both at >5{sigma} confidence).
- ID:
- ivo://CDS.VizieR/J/A+A/603/A68
- Title:
- Images of molecular and ionized gas around Sgr A*
- Short Name:
- J/A+A/603/A68
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report serendipitous detections of line emission with the Atacama Large Millimeter/submillimeter Array (ALMA) in bands 3, 6, and 7 in the central parsec down to within 1" around Sgr A* at an up to now highest resolution (<0.5") view of the Galactic center (GC) in the submillimeter (sub-mm) domain. From the 100GHz continuum and the H39{alpha} emission we obtain a uniform electron temperature around Te~6000K for the minispiral. The spectral index (S{prop.to}{nu}^{alpha}^) of Sagittarius A* (Sgr A*) is ~0.5 at 100-250GHz and ~0.0 at 230-340GHz. The bright sources in the center show spectral indices around -0.1 implying Bremsstrahlung emission, while dust emission is emerging in the minispiral exterior. Apart from CS, which is most widespread in the center, H^13^CO^+^, HC_3_N, SiO, SO, C_2_H, CH_3_OH, ^13^CS and N_2_H+ are also detected. The bulk of the clumpy emission regions is at positive velocities and in a region confined by the minispiral northern arm (NA), bar, and the sources IRS 3 and 7. Although partly spatially overlapping with the radio recombination line (RRL) emission at same negative velocities, the relation to the minispiral remains unclear. A likely explanation is an infalling clump consisting of denser cloud cores embedded in diffuse gas. This central association (CA) of clouds shows three times higher CS/X (X: any other observed molecule) ratios than the circumnuclear disk (CND) suggesting a combination of higher excitation, by a temperature gradient and/or infrared (IR) pumping, and abundance enhancement due to UV and/or X-ray emission. Hence, we conclude that this CA is closer to the center than the CND. Moreover, we find molecular line emission at velocities up to 200km/s. Apart from the CA, we identified two intriguing regions in the CND. One region shows emission in all molecular species and higher energy levels tested in this and previous observations and contains a methanol class I maser. The other region shows similar behavior of the line ratios such as the CA. Outside the CND, we find the traditionally quiescent gas tracer N_2_H^+^ coinciding with the largest IR dark clouds (IRDC) in the field. Methanol emission is found at and around previously detected methanol class I masers in the same region. We propose to make these particular regions subject to further studies in the scope of hot core, cold core, and extreme photon and/or X-ray dominated region (PDR/XDR) chemistry and consequent star formation in the central few parsecs.
- ID:
- ivo://CDS.VizieR/J/A+A/646/A104
- Title:
- Improving the open cluster census. I.
- Short Name:
- J/A+A/646/A104
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The census of open clusters in the Milky Way is in a never-before seen state of flux. Recent works have reported hundreds of new open clusters thanks to the incredible astrometric quality of the Gaia satellite, but other works have also reported that many open clusters discovered in the pre Gaia era may be associations. We aim to conduct a comparison of clustering algorithms used to detect open clusters, attempting to statistically quantify their strengths and weaknesses by deriving the sensitivity, specificity, and precision of each as well as their true positive rate against a larger sample. We selected DBSCAN, HDBSCAN, and Gaussian mixture models for further study, owing to their speed and appropriateness for use with Gaia data. We developed a preprocessing pipeline for Gaia data and developed the algorithms further for the specific application to open clusters. We derived detection rates for all 1385 open clusters in the fields in our study as well as more detailed performance statistics for 100 of these open clusters. DBSCAN was sensitive to 50%-62% of the true positive open clusters in our sample, with generally very good specificity and precision. HDBSCAN traded precision for a higher sensitivity of up to 82%, especially across different distances and scales of open clusters. Gaussian mixture models were slow and only sensitive to 33% of open clusters in our sample, which tended to be larger objects. Additionally, we report on 41 new open cluster candidates detected by HDBSCAN, three of which are closer than 500pc. When used with additional post-processing to mitigate its false positives, we have found that HDBSCAN is the most sensitive and effective algorithm for recovering open clusters in Gaia data. Our results suggest that many more new and already reported open clusters have yet to be detected in Gaia data.
- ID:
- ivo://CDS.VizieR/J/ApJ/737/73
- Title:
- Infrared extinction toward the Galactic Centre
- Short Name:
- J/ApJ/737/73
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We derive the extinction curve toward the Galactic center (GC) from 1 to 19um. We use hydrogen emission lines of the minispiral observed by ISO-SWS and SINFONI. The extinction-free flux reference is the 2cm continuum emission observed by the Very Large Array. Toward the inner 14"x20", we find an extinction of A_2.166um_=2.62+/-0.11, with a power-law slope of {alpha}=-2.11+/-0.06 shortward of 2.8um, consistent with the average near-infrared slope from the recent literature. At longer wavelengths, however, we find that the extinction is grayer than shortward of 2.8um. We find that it is not possible to fit the observed extinction curve with a dust model consisting of pure carbonaceous and silicate grains only, and the addition of composite particles, including ices, is needed to explain the observations. Combining a distance-dependent extinction with our distance-independent extinction, we derive the distance to the GC to be R_0_=7.94+/-0.65kpc. Toward Sgr A* (r<0.5"), we obtain A_H_=4.21+/-0.10, A_Ks_=2.42+/-0.10, and A_L'_=1.09+/-0.13.
- ID:
- ivo://CDS.VizieR/J/A+A/572/A63
- Title:
- Intensity maps in the star-forming complex W33
- Short Name:
- J/A+A/572/A63
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The object W33 is a giant molecular cloud that contains star forming regions at various evolutionary stages from quiescent clumps to developed HII regions. Since its star forming regions are located at the same distance and the primary material of the birth clouds is probably similar, we conducted a comparative chemical study to trace the chemical footprint of the different phases of evolution. We observed six clumps in W33 with the Atacama Pathfinder Experiment (APEX) telescope at 280GHz and the Submillimeter Array (SMA) at 230GHz. We detected 27 transitions of 10 different molecules in the APEX data and 52 transitions of 16 different molecules in the SMA data. The chemistry on scales larger than ~0.2pc, which are traced by the APEX data, becomes more complex and diverse the more evolved the star forming region is. On smaller scales traced by the SMA data, the chemical complexity and diversity increase up to the hot core stage. In the HII region phase, the SMA spectra resemble the spectra of the protostellar phase. Either these more complex molecules are destroyed or their emission is not compact enough to be detected with the SMA. Synthetic spectra modelling of the H_2_CO transitions, as detected with the APEX telescope, shows that both a warm and a cold component are needed to obtain a good fit to the emission for all sources except for W33 Main1. The temperatures and column densities of the two components increase during the evolution of the star forming regions. The integrated intensity ratios N_2_H^+^(3-2)/CS(6-5) and N_2_H^+^(3-2)/H_2_CO(4_2,2_-3_2,1_) show clear trends as a function of evolutionary stage, luminosity, luminosity-to-mass ratio, and H_2_ peak column density of the clumps and might be usable as chemical clocks.
- ID:
- ivo://CDS.VizieR/J/AJ/140/462
- Title:
- Intermediate-mass star-forming regions
- Short Name:
- J/AJ/140/462
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In an effort to understand the factors that govern the transition from low- to high-mass star formation, for the first time we identify a sample of intermediate-mass star-forming regions (IM SFRs) where stars up to (but not exceeding) ~8M_{sun}_ are being produced. We use IRAS colors and Spitzer Space Telescope mid-IR images, in conjunction with millimeter continuum and ^13^CO maps, to compile a sample of 50 IM SFRs in the inner Galaxy. These are likely to be precursors to Herbig AeBe stars and their associated clusters of low-mass stars.
- ID:
- ivo://CDS.VizieR/J/MNRAS/493/2339
- Title:
- Internal motions in OB-associations
- Short Name:
- J/MNRAS/493/2339
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We study the motions inside 28 OB-associations with the use of Gaia DR2 proper motions. The average velocity dispersion calculated for 28 OB-associations including more than 20 stars with Gaia DR2 proper motion is sigma_v_=4.5km/s. The median virial and stellar masses of OB-associations are 8.9x10^5^ and 8.1x10^3^M_{sun}_, respectively. The median star-formation efficiency in parent giant molecular clouds appears to be epsilon=1.2%. Gaia DR2 proper motions confirm the expansion in the Per OB1, Car OB1 and Sgr OB1 associations found earlier with Gaia DR1 data. We also detect the expansion in Gem OB1, Ori OB1 and Sco OB1 associations which became possible for the first time now when analyzed with Gaia DR2 proper motions. The analysis of the distribution of OB-stars in the Per OB1 association shows the presence of a shell-like structure with the radius of 40 pc. Probably, the expansion of the Per OB1 association started with the velocity greater than the present-day expansion velocity equal to 5.0+/-1.7km/s.
- ID:
- ivo://CDS.VizieR/J/A+A/495/157
- Title:
- Interstellar extinction in Galactic Center
- Short Name:
- J/A+A/495/157
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We use the Spitzer IRAC catalogue of the Galactic Center (GC) point sources (Ramirez et al., 2008ApJS..175..147R) and combine it with new isochrones (Marigo et al., 2008A&A...482..883M) to derive extinctions based on photometry of red giants and asymptotic giant branch (AGB) stars. This new extinction map extends to much higher values of Av than previously available. Our new extinction map of the GC region covers 2.0x1.4deg^2^ (280x200pc at a distance of 8kpc). We apply it to deredden the LPVs found by Glass et al. (2001, Cat. <J/MNRAS/321/77>) near the GC. We make period-magnitude diagrams and compare them to those from other regions of different metallicity. The Glass-LPVs follow well-defined period-luminosity relations (PL) in the IRAC filter bands at 3.6 , 4.5, 5.8, and 8.0um. The period-luminosity relations are similar to those in the Large Magellanic Cloud, suggesting that the PL relation in the IRAC bands is universal. We use ISOGAL data to derive mass-loss rates and find for the Gl ass-LPV sample some correlation between mass-loss and pulsation period, as expected theoretically. The GC has an excess of high luminosity and long period LPVs compared to the Bulge, which supports previous suggestions that it contains a younger stellar population.
