- ID:
- ivo://CDS.VizieR/J/ApJ/720/1055
- Title:
- VBLA observations of W51 Main/South
- Short Name:
- J/ApJ/720/1055
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report measurement of the trigonometric parallax of W51 Main/South using the Very Long Baseline Array. We measure a value of 0.185+/-0.010mas corresponding to a distance of 5.41^+0.31^_-0.28_kpc. W51 Main/South is a well-known massive star-forming region near the tangent point of the Sagittarius spiral arm of the Milky Way. Our distance to W51 yields an estimate of the distance to the Galactic center of R_0_=8.3+/-0.46(statistical)+/-1.0(systematic)kpc by simple geometry. Combining the parallax and proper motion measurements for W51, we obtained the full-space motion of this massive star-forming region. We find W51 is in a nearly circular orbit about the Galactic center. The H_2_O masers used for our parallax measurements trace four powerful bipolar outflows within a 0.4pc size region, some of which are associated with dusty molecular hot cores and/or hyper- or ultra-compact HII regions.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/582/756
- Title:
- Velocities of HII regions
- Short Name:
- J/ApJ/582/756
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Kinematic distance determinations in the inner Galaxy are hampered by the near-far kinematic distance ambiguity. Here we resolve the ambiguity for 49 HII region complexes with known recombination-line velocities in the first Galactic quadrant. We measured the 21cm HI absorption spectrum toward each source with the Very Large Array in the C array. The maximum velocity of HI absorption was used to discriminate between the near and far kinematic distances. The number ratio of far to near sources, ~3, can be entirely explained as a geometrical effect. The kinematic distances that we derive are compared with previous determinations for the same sources. Although our distance determinations are largely in agreement with previous measurements, there are 22 discrepancies that we discuss. Using our distance determinations, we create a face-on Galactic map of the HII region complexes and compare it with a kinematically derived profile of the distribution of CO-traced molecular hydrogen. The HII region complexes delineate the large-scale features seen in the molecular gas. The 5kpc molecular ring and the Sagittarius spiral arm are clearly evident, and a few HII region complexes lie in the Perseus arm.
- ID:
- ivo://CDS.VizieR/J/MNRAS/379/1237
- Title:
- VIcJHK photometry of NGC 1893 Halpha sources
- Short Name:
- J/MNRAS/379/1237
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using H{alpha} grism spectroscopy and optical and Two-Micron All-Sky Survey photometry of the fields containing NGC 1893 and two emission nebulae, Sim 129 and Sim 130, we show the presence of a number of H{alpha} and near-infrared excess sources towards the region between HD 242935 and the two emission nebulae. Among them a large majority of these pre-main-sequence candidate sources are concentrated towards regions closer to Sim 129 and Sim 130.
- ID:
- ivo://CDS.VizieR/J/BaltA/10/319
- Title:
- Vilnius photometry in NGC 1499
- Short Name:
- J/BaltA/10/319
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Vilnius seven-color photometry has been obtained for 238 stars down to 13th mag in the area of the California Nebula in Perseus. For nearly all of the stars photometric spectral classes, luminosity classes, absolute magnitudes, interstellar reddenings, extinctions and distances are determined. The present paper contains the results of photometry and the parameters of the stars.
- ID:
- ivo://CDS.VizieR/J/A+A/453/911
- Title:
- VLA and IR observations of the S235A-B region
- Short Name:
- J/A+A/453/911
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report on new aspects of the star-forming region S235AB revealed through high-resolution observations at radio and mid-infrared wavelengths. Using the Very Large Array, we carried out sensitive observations of S235AB in the cm continuum (6, 3.6, 1.3, and 0.7) and in the 22GHz water maser line. These were complemented with Spitzer Space Telescope Infrared Array Camera archive data to clarify the correspondence between radio and IR sources. We made also use of newly presented data from the Medicina water maser patrol, started in 1987, to study the variability of the water masers found in the region.
- ID:
- ivo://CDS.VizieR/J/ApJS/253/23
- Title:
- VLA 9GHz obs. of HII region candidates
- Short Name:
- J/ApJS/253/23
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Milky Way contains thousands of HII region candidates identified by their characteristic mid-infrared morphology, but lacking detections of ionized gas tracers such as radio continuum or radio recombination line emission. These targets thus remain unconfirmed as HII regions. With only ~2500 confirmed HII regions in the Milky Way, Galactic surveys are deficient by several thousand nebulae when compared to external galaxies with similar star formation rates. Using sensitive 9 GHz radio continuum observations with the Karl G. Jansky Very Large Array, we explore a sample of HII region candidates in order to set observational limits on the actual total population of Galactic HII regions. We target all infrared-identified "radio-quiet" sources from the Wide-field Infrared Survey Explorer Catalog of Galactic HII regions between 245{deg}>=l>=90{deg} with infrared diameters less than 80". We detect radio continuum emission from 50% of the targeted HII region candidates, providing strong evidence that most of the radio-quiet candidates are bona fide HII regions. We measure the peak and integrated radio flux densities and compare the inferred Lyman continuum fluxes using models of OB stars. We conclude that stars of approximately spectral type B2 and earlier are able to create HII regions with similar infrared and radio continuum morphologies as the more luminous HII regions created by O stars. From our 50% detection rate of "radio-quiet" sources, we set a lower limit of ~7000 for the HII region population of the Galaxy. Thus the vast majority of the Milky Way's HII regions remain to be discovered.
- ID:
- ivo://CDS.VizieR/J/ApJ/707/283
- Title:
- VLA observation of molecular clumps
- Short Name:
- J/ApJ/707/283
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have conducted a search for ionized gas at 3.6cm, using the Very Large Array, toward 31 Galactic intermediate- and high-mass clumps detected in previous millimeter continuum observations. In the 10 observed fields, 35 HII regions are identified, of which 20 are newly discovered. Many of the HII regions are multiply peaked indicating the presence of a cluster of massive stars. We find that the ionized gas tends to be associated toward the millimeter clumps; of the 31 millimeter clumps observed, nine of these appear to be physically related to ionized gas, and a further six have ionized gas emission within 1'. For clumps with associated ionized gas, the combined mass of the ionizing massive stars is compared to the clump masses to provide an estimate of the instantaneous star formation efficiency. These values range from a few percent to 25%, and have an average of 7%+/-8%. We also find a correlation between the clump mass and the mass of the ionizing massive stars within it, which is consistent with a power law. This result is comparable to the prediction of star formation by competitive accretion that a power-law relationship exists between the mass of the most massive star in a cluster and the total mass of the remaining stars.
- ID:
- ivo://CDS.VizieR/J/ApJS/244/35
- Title:
- VLA observations of the Central Molecular Zone
- Short Name:
- J/ApJS/244/35
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present new observations of the C-band continuum emission and masers to assess high-mass (>8M_{sun}_) star formation at early evolutionary phases in the inner 200pc of the Central Molecular Zone (CMZ) of the Galaxy. The continuum observation is complete to free-free emission from stars above 10-11M_{sun}_ in 91% of the covered area. We identify 104 compact sources in the continuum emission, among which five are confirmed ultracompact HII regions, 12 are candidates of ultracompact HII regions, and the remaining 87 sources are mostly massive stars in clusters, field stars, evolved stars, pulsars, extragalactic sources, or of unknown nature that is to be investigated. We detect class II CH_3_OH masers at 23 positions, among which six are new detections. We confirm six known H_2_CO masers in two high-mass star-forming regions and detect two new H_2_CO masers toward the Sgr C cloud, making it the ninth region in the Galaxy that contains masers of this type. In spite of these detections, we find that current high-mass star formation in the inner CMZ is only taking place in seven isolated clouds. The results suggest that star formation at early evolutionary phases in the CMZ is about 10 times less efficient than expected from the dense gas star formation relation, which is in line with previous studies that focus on more evolved phases of star formation. This means that if there will be any impending, next burst of star formation in the CMZ, it has not yet begun.
- ID:
- ivo://CDS.VizieR/J/ApJ/699/186
- Title:
- VLA observations of the Galactic center
- Short Name:
- J/ApJ/699/186
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present new results based on high-resolution observations of Sgr A West at the Galactic center with the Very Large Array (VLA) at 1.3cm. By combining recent observations with those made at earlier epochs with the VLA at wavelengths of 1.3 and 3.6cm, we measured proper motions for 71 compact HII components in the central 80" (3pc, assuming D=8pc). Using VLA archival data for the H92{alpha} radio recombination line, we also investigated radial velocities in the LSR velocity range from +200 to -415km/s. Combining proper motion and radial velocity measurements, we have determined the three-dimensional velocity distribution in Sgr A West.
- ID:
- ivo://CDS.VizieR/J/AJ/138/33
- Title:
- VLT JHKs imaging of RCW 38
- Short Name:
- J/AJ/138/33
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of high angular resolution adaptive optics (AO) near-infrared (JHKs) observations of the deeply embedded massive cluster RCW 38 using NACO on the Very Large Telescope. Narrowband AO observations centered at wavelengths of 1.28um, 2.12um, and 2.17um were also obtained. The area covered by these observations is about 0.5pc^2^, centered on the O-star RCW 38 IRS 2. We use the JHKs colors to identify young stars with infrared (IR) excess in this region.
