Viscosity Influence Research on Load Capacity of Heavy Hydrostatic Bearing

Zhang, Yan Qin; Xiao, Yu; Yang, Xiao Dong; Sun, Gui Tao; Yu, Xiao; Shi, Zhiming

doi:10.4028/www.scientific.net/kem.450.63

Cited by 16 publications

(14 citation statements)

References 4 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In earlier studies, also (3, 3), (10, 8), and (11, 9) maser emission has been reported (Mauersberger et al 1987;Zhang & Ho 1995). The (6, 3) line, which 25 years ago also contributed to the 54.5 km s −1 group of masers (Madden et al 1986), is now seen at ∼57 km s −1 (see above).…”

Section: Variability On Long Time Scalesmentioning

confidence: 76%

“…Figures 6 and 7 show spectra of ammonia lines with maser features being closer to the quasi-thermal "systemic" emission peaking near 60 km s −1 . Interestingly, the (3, 3) and (10, 8) lines, previously reported to exhibit maser emission at ∼54 km s −1 (Mauersberger et al 1987;Zhang & Ho 1995), now show exclusively the quasithermal 60 km s −1 component (Fig. 8).…”

Section: The Spectramentioning

confidence: 97%

“…Interferometric measurements to determine accurate positions have been carried out for the (3, 3) and (9, 8) maser lines (Gaume et al 1993;Zhang & Ho 1995 Sect. 4.3).…”

Section: Constraints For Pumping Scenariosmentioning

confidence: 99%

See 2 more Smart Citations

Ammonia in the hot core W 51-IRS2: 11 new maser lines and a maser component with a velocity drift

Henkel

Wilson

Asiri

et al. 2013

A&A

View full text Add to dashboard Cite

With the 100-m telescope at Effelsberg, 19 ammonia (NH 3 ) maser lines have been detected toward the prominent massive star forming region W51-IRS2. Eleven of these inversion lines, the (J, K) = (6, 2), (5, 3), (7, 4), (8, 5), (7, 6), (7, 7), (9, 7), (10, 7), (9, 9), (10, 9), and (12, 12) transitions, are classified as masers for the first time in outer space. All detected masers are related to highly excited inversion doublets. The (5, 4) maser originates from an inversion doublet ∼340 K above the ground state, while the (12, 12) transition, at ∼1450 K, is the most highly excited NH 3 maser line so far known. Strong variability is seen not only in ortho-but also in para-NH 3 transitions. Bright narrow emission features are observed, for the first time, in (mostly) ortho-ammonia transitions, at V LSR ∼ 45 km s −1 , well separated from the quasi-thermal emission near 60 km s −1 . These features were absent ∼25 years ago and show a velocity drift of about +0.2 km s −1 yr −1 . The component is likely related to the SiO maser source in W51-IRS2 and a possible scenario explaining the velocity drift is outlined. The 57 km s −1 component of the (9, 6) maser line is found to be strongly linearly polarised. Maser emission in the (J, K) to (J + 1, K) inversion doublets is strictly forbidden by selection rules for electric dipole transitions in the ground vibrational state. However, such pairs (and even triplets with (J + 2, K)) are common toward W51-IRS2. Similarities in line widths and velocities indicate that such groups of maser lines arise from the same regions, which can be explained by pumping through vibrational excitation. The large number of NH 3 maser lines in W51-IRS2 is most likely related to the exceptionally high kinetic temperature and NH 3 column density of this young massive star forming region.

show abstract

Section: Variability On Long Time Scalesmentioning

confidence: 76%

Section: The Spectramentioning

confidence: 97%

See 1 more Smart Citation

Ammonia in the hot core W 51-IRS2: 11 new maser lines and a maser component with a velocity drift

Henkel

Wilson

Asiri

et al. 2013

A&A

View full text Add to dashboard Cite

show abstract

“…(Figure 14). In addition, there are several compact and UCH II regions that are not detected at <20µm because of heavy extinction (Gaume et al 1993;Zhang & Ho 1995.…”

Section: Sed Models For Mysosmentioning

confidence: 99%

Young Stellar Objects in the Massive Star-forming Regions W51 and W43

Saral

Hora

Audard

et al. 2017

ApJ

View full text Add to dashboard Cite

We present the results of our investigation of the star-forming complexes W51 and W43, two of the brightest in the first Galactic quadrant. In order to determine the young stellar object (YSO) populations in W51 and W43 we used color-magnitude relations based on Spitzer mid-infrared and 2MASS/UKIDSS near-infrared data. We identified 302 Class I YSOs and 1178 Class II/transition disk candidates in W51, and 917 Class I YSOs and 5187 Class II/transition disk candidates in W43. We also identified tens of groups of YSOs in both regions using the Minimal Spanning Tree (MST) method. We found similar cluster densities in both regions, even though Spitzer was not able to probe the densest part of W43. By using the Class II/I ratios, we traced the relative ages within the regions, and based on the morphology of the clusters, we argue that several sites of star formation are independent of one another in terms of their ages and physical conditions. We used spectral energy distribution-fitting to identify the massive YSO (MYSO) candidates since they play a vital role in the star formation process, and then examined them to see if they are related to any massive star formation tracers such as UCH II regions, masers, or dense fragments. We identified 17 MYSO candidates in W51, and 14 in W43, respectively, and found that groups of YSOs hosting MYSO candidates are positionally associated with H II regions in W51, though we do not see any MYSO candidates associated with previously identified massive dense fragments in W43.

show abstract

“…The region shows widespread NH 3 thermal emission (Zhang & Ho 1997) as well as strong maser emission from OH, CH 3 OH, H 2 O, and NH 3 (Zhang & Ho 1995;Imai et al 2002;Fish & Reid 2007;Etoka et al 2012;Surcis et al 2012).…”

Section: Introductionmentioning

confidence: 99%

Hot ammonia around young O-type stars

Goddi

Ginsburg²,

Zhang

2016

A&A

View full text Add to dashboard Cite

Context. This paper is the third in a series of NH 3 multilevel imaging studies in well-known, high-mass star-forming regions. The main goal is to characterize kinematics and physical conditions of (hot and dense) circumstellar molecular gas around O-type young stars. Aims. We want to map at subarcsecond resolution highly excited inversion lines of NH 3 in the high-mass star-forming region W51 Main (distance = 5.4 kpc), which is an ideal target to constrain theoretical models of high-mass star formation. Methods. Using the Karl Jansky Very Large Array (JVLA), we mapped the hot and dense molecular gas in W51 Main with ∼0. 2−0. 3 angular resolution in five metastable (J = K) inversion transitions of ammonia (NH 3 ): (J, K) = (6, 6), (7, 7), (9, 9), (10, 10), and (13, 13). These lines arise from energy levels between ∼400 K and ∼1700 K above the ground state. We also made maps of the (free-free) continuum emission at frequencies between 25 and 36 GHz. Results. We have identified and characterized two main centers of high-mass star formation in W51 Main, which excite hot cores and host one or multiple high-mass young stellar objects (YSOs) at their centers: the W51e2 complex and the W51e8 core (∼6 southward of W51e2). The former breaks down into three further subcores: W51e2-W, which surrounds the well-known hypercompact (HC) HII region, where hot NH 3 is observed in absorption, and two additional dusty cores, W51e2-E (∼0. 8 to the East) and W51e2-NW (∼1 to the North), where hot NH 3 is observed in emission. The velocity maps toward the HC HII region show a clear velocity gradient along the east-west in all lines. The gradient may indicate rotation, although any Keplerian motion must be on smaller scales (<1000 AU) as we do not directly observe a Keplerian velocity profile. The absence of outflow and/or maser activity and the low amount of molecular gas available for accretion (∼5 M , assuming [NH 3 ]/[H 2 ] = 10 −7 ) with respect to the mass of the central YSO estimated from radio luminosity (>20 M ), both indicate that the central YSO has already accreted most of its final mass. On the other hand, the nearby W51e2-E, while not showing evidence of rotation, shows signatures of infall in a hot dense core (T ∼ 170 K, n H 2 ∼ 5 × 10 7 cm −3 ), based on asymmetric spectral profiles (skewed toward the blueshifted component) in optically thick emission lines of NH 3 . The relatively large amount of hot molecular gas available for accretion (∼20 M within about half an arcsecond or 2500 AU), along with strong outflow and maser activity, indicates that the main accretion center in the W51e2 complex is W51e2-E rather than W51e2-W. Finally, W51e2-NW and W51e8, although less dense (n H 2 ∼ 2 × 10 7 cm −3 and ∼3 × 10 6 cm −3 ), are also hot cores (T gas ∼ 140 and 200 K) and contain a significant amount of molecular gas (M gas ∼ 30 M and ∼70 M , respectively). We speculate that they may host high-mass YSOs either at a previous evolutionary stage or with a mass that is lower than W51e2-E and W51e2-W. Conclusions. Using h...

show abstract

Viscosity Influence Research on Load Capacity of Heavy Hydrostatic Bearing

Cited by 16 publications

References 4 publications

Ammonia in the hot core W 51-IRS2: 11 new maser lines and a maser component with a velocity drift

Ammonia in the hot core W 51-IRS2: 11 new maser lines and a maser component with a velocity drift

Young Stellar Objects in the Massive Star-forming Regions W51 and W43

Hot ammonia around young O-type stars

Contact Info

Product

Resources

About