- ID:
- ivo://CDS.VizieR/J/ApJ/880/9
- Title:
- Spitzer obs. of YSOs in the SMOG field
- Short Name:
- J/ApJ/880/9
- Date:
- 07 Mar 2022 07:09:50
- Publisher:
- CDS
- Description:
- In this paper we undertake a study of the 21deg^2^ SMOG field, a Spitzer cryogenic mission Legacy program to map a region of the outer Milky Way toward the Perseus and outer spiral arms with the IRAC and MIPS instruments. We identify 4648 YSOs across the field. Using the DBSCAN method, we identify 68 clusters or aggregations of YSOs in the region, having eight or more members. We identify 1197 Class I objects, 2632 Class II objects, and 819 Class III objects, of which 45 are candidate transition disk objects, utilizing the MIPS 24 photometry. The ratio of YSOs identified as members of clusters was 2872/4648, or 62%. The ratios of Class I to Class II YSOs in the clusters are broadly consistent with those found in the inner Galactic and nearby Gould Belt young star formation regions. The clustering properties indicate that the protostars may be more tightly bound to their natal sites than the Class II YSOs, and the Class III YSOs are generally widely distributed. We further perform an analysis of the WISE data of the SMOG field to determine how the lower resolution and sensitivity of WISE affects the identification of YSOs as compared to Spitzer: we identify 931 YSOs using combined WISE and 2MASS photometry, or 20% (931/4648) of the total number identified with Spitzer. Performing the same clustering analysis finds 31 clusters that reliably trace the larger associations identified with the Spitzer data. Twelve of the clusters identified have previously measured distances from the WISE HII survey. SEDFitter modeling of these YSOs is reported, leading to an estimation of the initial mass function in the aggregate of these clusters that approximates that found in the inner Galaxy, implying that the processes behind stellar mass distribution during star formation are not widely affected by the lower density and metallicity of the outer Galaxy.
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Search Results
- ID:
- ivo://CDS.VizieR/J/AJ/157/12
- Title:
- Star clusters, associations, & candidates in the MW
- Short Name:
- J/AJ/157/12
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a catalog of Galactic star clusters, associations and candidates with 10978 entries. This multi-band catalog was constructed over 20 years, starting with visual inspections on the Digital Sky Survey and incremented with the 2MASS, WISE, VVV, Spitzer, and Herschel surveys. Large and small catalogs, as well as papers on individual objects have been systematically cross-identified. The catalog provides Galactic and equatorial coordinates, angular diameters, and chronologically ordered designations, making it simple to assign discoveries and verify how often the objects were cataloged by different authors, search methods, and/or surveys. Detection in a single band is the minimum constraint to validate an entry. About 3200 objects have measured parameters in the literature. A fundamental contribution of the present study is to present an additional ~7700 objects for the first analyses of nature, photometry, spectroscopy and structure. The present focus is not to compile or determine fundamental parameters, but to provide a catalog uniformly characterizing the entries. A major result is that now 4234 embedded clusters are cataloged, a factor of ~1.5 larger than open clusters. In addition to cross-identifications in different references and wavelength domains, we also communicate the discovery of 638 star clusters and similar objects. The present general catalog provides previously studied objects and thousands of additional entries in a homogeneous way, a timely contribution to Gaia-related works.
- ID:
- ivo://CDS.VizieR/J/A+A/588/A29
- Title:
- Star formation in massive clumps in Milky Way
- Short Name:
- J/A+A/588/A29
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Newborn stars form within the localized, high density regions of molecular clouds. The sequence and rate at which stars form in dense clumps and the dependence on local and global environments are key factors in developing descriptions of stellar production in galaxies. We seek to observationally constrain the rate and latency of star formation in dense massive clumps that are distributed throughout the Galaxy and to compare these results to proposed prescriptions for stellar production. A sample of 24 micron based Class I protostars are linked to dust clumps that are embedded within molecular clouds selected from the APEX Telescope Large Area Survey of the Galaxy. We determine the fraction of star-forming clumps that imposes a constraint on the latency of star formation in units of a clump's lifetime. Protostellar masses are estimated from models of circumstellar environments of young stellar objects from which star formation rates are derived. Physical properties of the clumps are calculated from 870 micron dust continuum emission and NH_3_ line emission. Linear correlations are identified between the star formation rate surface density, Sigma_SFR and the quantities Sigma_H2/tau_ff and Sigma_H2/tau_cross, suggesting that star formation is regulated at the local scales of molecular clouds. The measured fraction of star forming clumps is 23%. Accounting for star formation within clumps that are excluded from our sample due to 24 micron saturation, this fraction can be as high as 31%, which is similar to previous results. Dense, massive clumps form primarily low mass (<1-2M_{sun}_) stars with emergent 24 micron fluxes below our sensitivity limit or are incapable of forming any stars for the initial 70% of their lifetimes. The low fraction of star forming clumps in the Galactic center relative to those located in the disk of the Milky Way is verified.
- ID:
- ivo://CDS.VizieR/J/ApJ/752/146
- Title:
- Star forming complexes in Galactic WMAP sources
- Short Name:
- J/ApJ/752/146
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We analyze Spitzer GLIMPSE, Midcourse Space Experiment (MSX), and Wilkinson Microwave Anisotropy Probe (WMAP) images of the Milky Way to identify 8{mu}m and free-free sources in the Galaxy. Seventy-two of the 88 WMAP sources have coverage in the GLIMPSE and MSX surveys suitable for identifying massive star-forming complexes (SFCs). We measure the ionizing luminosity functions of the SFCs and study their role in the turbulent motion of the Galaxy's molecular gas. We find a total Galactic free-free flux f_{nu}_=46177.6Jy; the 72 WMAP sources with full 8{mu}m coverage account for 34263.5Jy (~75%), with both measurements made at {nu}=94GHz (W band). We find a total of 280 SFCs, of which 168 have unique kinematic distances and free-free luminosities. We use a simple model for the radial distribution of star formation to estimate the free-free and ionizing luminosity for the sources lacking distance determinations. The total dust-corrected ionizing luminosity is Q=(2.9+/-0.5)x10^53^photons/s, which implies a Galactic star formation rate of \dot{M}_{star}_=1.2+/-0.2{M}_{sun}_/yr. We present the (ionizing) luminosity function of the SFCs and show that 24 sources emit half the ionizing luminosity of the Galaxy. The SFCs appear as bubbles in GLIMPSE or MSX images; the radial velocities associated with the bubble walls allow us to infer the expansion velocity of the bubbles. We calculate the kinetic luminosity of the bubble expansion and compare it to the turbulent luminosity of the inner molecular disk. SFCs emitting 80% of the total Galactic free-free luminosity produce a kinetic luminosity equal to 65% of the turbulent luminosity in the inner molecular disk. This suggests that the expansion of the bubbles is a major driver of the turbulent motion of the inner Milky Way molecular gas.
- ID:
- ivo://CDS.VizieR/J/A+A/624/L8
- Title:
- Starlight polarization
- Short Name:
- J/A+A/624/L8
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Galactic dust emission is polarized at unexpectedly high levels, as revealed by Planck. The origin of the observed 20% polarization fractions can be identified by characterizing the properties of optical starlight polarization in a region with maximally polarized dust emission. We measure the R-band linear polarization of 22 stars in a region with a submillimeter polarization fraction of 20%. A subset of 6 stars is also measured in the B, V, and I bands to investigate the wavelength dependence of polarization. We find that starlight is polarized at correspondingly high levels. Through multiband polarimetry we find that the high polarization fractions are unlikely to arise from unusual dust properties, such as enhanced grain alignment. Instead, a favorable magnetic field geometry is the most likely explanation, and is supported by observational probes of the magnetic field morphology. The observed starlight polarization exceeds the classical upper limit of [pV/E(B-V]_{max}_=9%/mag and is at least as high as 13%/mag, as inferred from a joint analysis of Planck data, starlight polarization and reddening measurements. Thus, we confirm that the intrinsic polarizing ability of dust grains at optical wavelengths has long been underestimated.
- ID:
- ivo://CDS.VizieR/J/ApJ/821/44
- Title:
- Star motions in the nuclear cluster of the MW
- Short Name:
- J/ApJ/821/44
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We obtain the basic properties of the nuclear cluster of the Milky Way. First, we investigate the structural properties by constructing a stellar density map of the central 1000" using extinction-corrected old star counts from VISTA, WFC3/IR, and VLT/NACO data. We describe the data using two components. The inner, slightly flattened (axis ratio of q=0.80+/-0.04) component is the nuclear cluster, while the outer component corresponds to the stellar component of the circumnuclear zone. For the nuclear cluster, we measure a half-light radius of 178+/-51"~7+/-2pc and a luminosity of M_Ks_=-16.0+/-0.5. Second, we measure detailed dynamics out to 4pc. We obtain 10351 proper motions from AO data, and 2513 radial velocities from VLT/SINFONI data. We determine the cluster mass by means of isotropic spherical Jeans modeling. We fix the distance to the Galactic Center and the mass of the supermassive black hole. We model the cluster either with a constant M/L or with a power law. For the latter case, we obtain a slope of 1.18+/-0.06. We get a cluster mass within 100" of M_100"_=(6.09+/-0.53|_fixR_0_+/-0.97|_R_0_)x10^6^M_{sun}_ for both modeling approaches. A model which includes the observed flattening gives a 47% larger mass (see Chatzopoulos et al. 2015MNRAS.447..948C). Our results slightly favor a core over a cusp in the mass profile. By minimizing the number of unbound stars within 8", we obtain a distance of R_0_=8.53_-0.15_^+0.21^kpc when using an R0 supermassive black hole mass relation from stellar orbits. Combining our results, we obtain M/L=0.51+/-0.12M_{sun}/L_{sun},Ks_, which is roughly consistent with a Chabrier IMF.
- ID:
- ivo://CDS.VizieR/J/ApJ/749/71
- Title:
- Star polarization in the Galactic plane
- Short Name:
- J/ApJ/749/71
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This work combines new observations of NIR starlight linear polarimetry with previously simulated observations in order to constrain dynamo models of the Galactic magnetic field. Polarimetric observations were obtained with the Mimir instrument on the Perkins Telescope in Flagstaff, AZ, along a line of constant Galactic longitude ({ell}=150{deg}) with 17 pointings of the 10'x10' field of view between -75{deg}<b<10{deg}, with more frequent pointings toward the Galactic midplane. A total of 10962 stars were photometrically measured and 1116 had usable polarizations. The observed distribution of polarization position angles with Galactic latitude and the cumulative distribution function of the measured polarizations are compared to predicted values. While the predictions lack the effects of turbulence and are therefore idealized, this comparison allows significant rejection of A0-type magnetic field models. S0 and disk-even halo-odd magnetic field geometries are also rejected by the observations, but at lower significance. New predictions of spiral-type, axisymmetric magnetic fields, when combined with these new NIR observations, constrain the Galactic magnetic field spiral pitch angle to -6{deg}+/-2{deg}.
- ID:
- ivo://CDS.VizieR/J/ApJ/714/663
- Title:
- Stellar density map of the Milky Way
- Short Name:
- J/ApJ/714/663
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We map the stellar structure of the Galactic thick disk and halo by applying color-magnitude diagram (CMD) fitting to photometric data from the Sloan Extension for Galactic Understanding and Exploration (SEGUE) survey. The SEGUE imaging scans allow, for the first time, a comprehensive analysis of Milky Way structure at both high and low latitudes using uniform Sloan Digital Sky Survey photometry. Incorporating photometry of all relevant stars simultaneously, CMD fitting bypasses the need to choose single tracer populations. Using old stellar populations of differing metallicities as templates, we obtain a sparse three-dimensional map of the stellar mass distribution at |Z|>1kpc. Fitting a smooth Milky Way model comprising exponential thin and thick disks and an axisymmetric power-law halo allows us to constrain the structural parameters of the thick disk and halo. The thick-disk scale height and length are well constrained at 0.75+/-0.07kpc and 4.1+/-0.4kpc, respectively.
- ID:
- ivo://CDS.VizieR/J/A+A/653/A72
- Title:
- Stellar parameters and Li abundances from GES iDR6
- Short Name:
- J/A+A/653/A72
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- After more than 50 years, astronomical research still struggles to reconstruct the history of lithium enrichment in the Galaxy and to establish the relative importance of the various ^7^Li sources in enriching the interstellar medium (ISM) with this fragile element. To better trace the evolution of lithium in the Milky Way discs, we exploit the unique characteristics of a sample of open clusters (OCs) and field stars for which high-precision ^7^Li abundances and stellar parameters are homogeneously derived by the Gaia-ESO Survey (GES). We derive possibly un-depleted ^7^Li abundances for 26 OCs and star forming regions with ages from young (~3Myr) to old (~4.5Gyr), spanning a large range of galactocentric distances, 5<RGC/kpc<15, which allows us to reconstruct the local late Galactic evolution of lithium as well as its current abundance gradient along the disc. Field stars are added to look further back in time and to constrain ^7^Li evolution in other Galactic components. The data are then compared to theoretical tracks from chemical evolution models that implement different ^7^Li forges. Thanks to the homogeneity of the GES analysis, we can combine the maximum average ^7^Li abundances derived for the clusters with ^7^Li measurements in field stars. We find that the upper envelope of the ^7^Li abundances measured in field stars of nearly solar metallicities (-0.3<[Fe/H]/dex<+0.3) traces very well the level of lithium enrichment attained by the ISM as inferred from observations of cluster stars in the same metallicity range. We confirm previous findings that the abundance of ^7^Li in the solar neighbourhood does not decrease at supersolar metallicity. The comparison of the data with the chemical evolution model predictions favours a scenario in which the majority of the ^7^Li abundance in meteorites comes from novae. Current data also seem to suggest that the nova rate flattens out at later times. This requirement might have implications for the masses of the white dwarf nova progenitors and deserves further investigation. Neutrino-induced reactions taking place in core-collapse supernovae also produce some fresh lithium. This likely makes a negligible contribution to the meteoritic abundance, but could be responsible for a mild increase in the ^7^Li abundance in the ISM of low-metallicity systems that would counterbalance the astration processes.
- ID:
- ivo://CDS.VizieR/J/AJ/159/287
- Title:
- Stellar parameters in Ophiuchus Stream with MMT
- Short Name:
- J/AJ/159/287
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present new kinematic data for the Ophiuchus stellar stream. Spectra have been taken of member candidates at the Multiple Mirror Telescope (MMT) using Hectospec, Hectochelle, and Binospec, which provide more than 1800 new velocities. Combined with proper-motion measurements of stars in the field by the Gaia-DR2 catalog, we have derived stream membership probabilities, resulting in the detection of more than 200 likely members. These data show the stream extends to more than three times the length shown in the discovery data. A spur to the main stream is also detected. The high-resolution spectra allow us to resolve the stellar velocity dispersion, found to be 1.6{+/-}0.3km/s.
