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24121. WMAP 3-yr sources at 16 and 33GHz. II.
ID:
ivo://CDS.VizieR/J/MNRAS/400/995
Title:
WMAP 3-yr sources at 16 and 33GHz. II.
Short Name:
J/MNRAS/400/995
Date:
21 Oct 2021
Publisher:
CDS
Description:
Using the Arcminute Microkelvin Imager (AMI) at 16GHz and the Very Small Array (VSA) at 33GHz to make follow-up observations of sources in the New Extragalactic WMAP Point Source catalogue, we have investigated the flux density variability in a complete sample of 97 sources over time-scales of a few months to ~1.5yr.
24122. W. M. Keck Observatory
ID:
ivo://KeckObs/KeckObs
Title:
W. M. Keck Observatory
Short Name:
Keck
Date:
04 Apr 2008 16:43:32
Publisher:
W. M. Keck Observatory, CARA
Description:
The Keck Observatory's instruments are the twin Keck Telescopes, the world's largest optical and infrared telescopes. Each stands eight stories tall and weighs 300 tons, yet operates with nanometer precision. At the heart of each Keck Telescope is a revolutionary primary mirror. Ten meters in diameter, the mirror is composed of 36 hexagonal segments that work in concert as a single piece of reflective glass.
24123. W. M. Keck Observatory Archive
ID:
ivo://msc.koa/hires
Title:
W. M. Keck Observatory Archive
Short Name:
KOA
Date:
11 Jul 2006 18:51:46
Publisher:
Michelson Science Center
Description:
The W. M. Keck Observatory Archive (KOA) serves level 0 (uncalibrated) observations made with the CCD mosaic upgrade to the High Resolution Echelle Spectrograph (HIRES), commissioned on the Keck Telescope in August 2004. The data are subject to the proprietary policy agreed upon by NASA and the California Association for Research in Astronomy (CARA).
24124. W. M. Keck Observatory Archive
ID:
ivo://msc.koa
Title:
W. M. Keck Observatory Archive
Short Name:
KOA
Date:
11 Jul 2006 14:21:22
Publisher:
Michelson Science Center
Description:
This resource represents the naming authority for the Michelson Science Center and the W. M. Keck Observatory Archive (KOA)
24125. W43-MM1 ALMA ^12^CO(2-1) datacube
ID:
ivo://CDS.VizieR/J/A+A/636/A38
Title:
W43-MM1 ALMA ^12^CO(2-1) datacube
Short Name:
J/A+A/636/A38
Date:
21 Oct 2021
Publisher:
CDS
Description:
The accretion history of protostars remains widely mysterious even though it represents one of the best ways to understand the protostellar collapse that leads to the formation of stars. Molecular outflows, which are easier to detect than the direct accretion onto the prostellar embryo, are here used to characterize the protostellar accretion phase in W43-MM1. The W43-MM1 protocluster hosts a sufficient number of protostars to statistically investigate molecular outflows in a single, homogeneous region. We used the CO(2-1) and SiO(5-4) line datacubes, taken as part of an ALMA mosaic with a 2000 AU resolution, to search for protostellar outflows, evaluate the influence that the environment has on these outflows' characteristics and put constraints on outflow variability in W43-MM1. We discovered a rich cluster of 46 outflow lobes, driven by 27 protostars with masses of 1-100M_{sun}_. The complex environment inside which these outflow lobes develop has a definite influence on their length, limiting the validity of using outflow's dynamical timescales as a proxy of the ejection timescale in clouds with high dynamics and varying conditions. We performed a detailed study of Position-Velocity (PV) diagrams of outflows that revealed clear events of episodic ejection. The time variability of W43-MM1 outflows is a general trend and is more generally observed than in nearby, low- to intermediate-mass star-forming regions. The typical timescale found between two ejecta, ~500yr, is consistent with that found in nearby protostars. If ejection episodicity reflects variability in the accretion process, either protostellar accretion is more variable or episodicity is easier to detect in high-mass star-forming regions than in nearby clouds. The timescale found between accretion events could be resulting from instabilities, associated with bursts of inflowing gas arising from the close dynamical environment of highmass star-forming cores.
24126. W49N H2O maser outflow: distance and kinematics
ID:
ivo://CDS.VizieR/J/ApJ/393/149
Title:
W49N H2O maser outflow: distance and kinematics
Short Name:
J/ApJ/393/149
Date:
21 Oct 2021
Publisher:
CDS
Description:
Study of the motions of 105 H2O maser features clustered around a newly formed star in W49N yields the kinematics of the gas flow, the distance to the source, and the spatial scale of the Milky Way. We find that the maser outflow is bipolar, with an opening angle of ~60deg and an inclination of ~40deg to the line of sight. The expansion has a constant velocity of ~18 km/s out to a radius of 0.1pc, beyond which the outflow velocity increases to greater than 200 km/s. This increase may be due to interaction with ambient material. A rotation is also present; this rotation is nearly perpendicular to the outflow axis. The rotation may be due to ram pressure from ambient material; rotation of the ring of H II regions described by Welch et al. could produce such nonradial motion. Comparison of Doppler velocities and proper motions yields a distance of 11.4+/-1.2 kpc for the maser cluster. Combining this with a kinematic distance for W49N from Galactic rotation, we obtain a value of R0, the distance to the Galactic center, of 8.1+/-1.1 kpc.
24127. W49N H2O masers
ID:
ivo://CDS.VizieR/J/ApJ/429/253
Title:
W49N H2O masers
Short Name:
J/ApJ/429/253
Date:
21 Oct 2021
Publisher:
CDS
Description:
VLBI observations of a H2O maser were done at five epochs in 1980-82 with a 5 station VLBI network (see 1992ApJ...393..149G). A model was fitted to each peak in any spectral channel exceeding 5 times the rms background. The minimum level of this background, due to system noise at the antennas, was about 0.2Jy at each epoch. The model parameters include right ascension and declination offset (x, y) relative to a reference position; the total flux density, S; and the angular diameter {theta}_H_, of the best-fitting Gaussian distribution of intensity. The fitted parameters are in table1.
24128. W51 North ALMA 1.3 and 3mm images
ID:
ivo://CDS.VizieR/J/A+A/657/A30
Title:
W51 North ALMA 1.3 and 3mm images
Short Name:
J/A+A/657/A30
Date:
21 Mar 2022 09:31:18
Publisher:
CDS
Description:
The fragmentation process in massive star-forming regions is one of the contemporary problems in astrophysics, and several physical processes have been proposed to control the fragmentation including turbulence, magnetic field, rotation, stellar feedback, and gravity. However, the fragmentation process has been poorly studied at small spatial scales well below 1000AU. W51 IRS2 is a well known massive star-forming region whose fragmentation properties have not been well investigated yet. We aim to use ALMA (Atacama Large Millimeter and Submillimeter Array) high angular resolution data to identify the fragments in W51 IRS2 and to study the fragmentation properties on a spatial scale of 0.04" (200AU). We used ALMA data of W51 IRS2 from three projects, which give an angular resolution of 0.028" (144AU) at millimeter wavelengths. The continuum images reveal significant substructure in an east-west ridge, where both W51 North and W51d2 are embedded. A spectral index map has been generated from the 3 and 1.3mm high-resolution continuum images.We identified compact fragments by using uv-range constrained 1.3mm continuum data. A Mean Surface Density of Companions (MSDC) analysis has been performed to study the separations between fragments. A total number of 33 continuum sources are identified and 29 out of them are defined as fragments in the surveyed region.The MSDC analysis reveals two breaks corresponding to spatial sales of 1845AU and 7346AU, indicative of a two-level clustering phenomenon, along with a linear regime below 1845AU, mostly associated with W51 North, whose slope is consistent with the slope for the clustering regime of other cluster-like regions in the Galaxy. The typical masses and separations of the fragments as well as the relation between density and number of fragments can be explained through a thermal Jeans process operating at high temperatures of 200-400K, consistent with previous measurements of the temperature in the region, and produced by the nearby massive stars. Therefore, although W51 IRS2 seems to be undergoing a thermally inhibited fragmentation phase, this does not seem to prevent the formation of a protocluster associated with W51 North.
24129. W51 OB stars NIR spectroscopy
ID:
ivo://CDS.VizieR/J/A+A/624/A63
Title:
W51 OB stars NIR spectroscopy
Short Name:
J/A+A/624/A63
Date:
21 Oct 2021
Publisher:
CDS
Description:
The interplay between the formation of stars, stellar feedback and cloud properties strongly influences the star formation history of giant molecular clouds. The formation of massive stars leads to a variety of stellar clusters, ranging from low stellar density OB associations to dense, gravitationally bound starburst clusters. We aimed at identifying the massive stellar content and reconstructing the star formation history of the W51 giant molecular cloud. We performed near-infrared imaging and K-band spectroscopy of the massive stars in W51. We analysed the stellar populations using colour-magnitude and colour-colour diagrams and compared the properties of the spectroscopically identified stars with stellar evolution models. We derive the ages of the different sub-clusters in W51 and, based on our spectroscopy derive an age for W51 of 3Myrs or less. The age of the P Cygni star LS1 and the presence of two still forming proto- clusters suggests that the star formation history of W51 is more complex than a single burst. We did not find evidence for triggered star formation and we concluded that the star formation in W51 is multi seeded. We finally concluded that W51 is a OB association where different sub-clusters form over a time span of at least 3-5Myrs.
24130. WOCS. LXV. Abundances in NGC 6819
ID:
ivo://CDS.VizieR/J/AJ/149/121
Title:
WOCS. LXV. Abundances in NGC 6819
Short Name:
J/AJ/149/121
Date:
21 Oct 2021
Publisher:
CDS
Description:
High-dispersion spectra of 333 stars in the open cluster NGC 6819, obtained using the HYDRA spectrograph on the WIYN 3.5m telescope, have been analyzed to determine the abundances of iron and other metals from lines in the 400{AA} region surrounding the Li6708{AA} line. Our spectra, with signal-to-noise per pixel ranging from 60 to 300, span the luminosity range from the tip of the red giant branch to a point two magnitudes below the top of the cluster turnoff. We derive radial and rotational velocities for all stars, as well as [Fe/H] based on 17 iron lines, [Ca/H], [Si/H], and [Ni/H] in the 247 most probable, single members of the cluster. Input T_eff_ estimates for model atmosphere analysis are provided by (B-V) colors merged from several sources, with individual reddening corrections applied to each star relative to a cluster mean of E(B-V)=0.16. Extensive use is made of ROBOSPECT, an automatic equivalent width measurement program; its effectiveness on large spectroscopic samples is discussed. From the sample of likely single members, [Fe/H]=-0.03+/-0.06, where the error describes the median absolute deviation about the sample median value, leading to internal precision for the cluster below 0.01dex. The final uncertainty in the cluster abundance is therefore dominated by external systematics due to the temperature scale, surface gravity, and microturbulent velocity, leading to [Fe/H]=-0.02+/-0.02 for a sub-sample restricted to main sequence and turnoff stars. This result is consistent with our recent intermediate-band photometric determination of a slightly subsolar abundance for this cluster. [Ca/Fe], [Si/Fe], and [Ni/Fe] are determined to be solar within the uncertainties. NGC 6819 has an abundance distribution typical of solar metallicity thin disk stars in the solar neighborhood.

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