scholarly journals 1.5. SiO maser sources in the Galactic bulge and a kinematic signature of the bar structure

1998 ◽  
Vol 184 ◽  
pp. 25-26
Author(s):  
S. Deguchi
Keyword(s):  
Central Region ◽  
Radial Velocities ◽  
Kinematic Structure ◽  
Agb Stars ◽  
Galactic Bulge ◽  
The Galaxy ◽  
Forbidden Regions ◽  
Maser Sources

We are studying the kinematic structure of our Galaxy by detecting SiO maser lines around 43 GHz with the Nobeyama 45-m telescope. Till today, about 500 IRAS sources (AGB stars) in the central region of the Galaxy are observed and the radial velocities of about 300 detected sources are obtained. The longitude-velocity map of SiO sources clearly shows a presence of forbidden regions (holes) which are located at the same positions of HI and CO holes. The presence of holes is interpreted as a streaming motions of stars due to a bar structure of the Galactic bulge

scholarly journals The Age of Old Galactic Populations

1998 ◽  
Vol 11 (1) ◽  
pp. 560-561
Author(s):  
M. Grenon
Keyword(s):  
High Velocity ◽  
Radial Velocities ◽  
Thick Disk ◽  
Early Evolution ◽  
Galactic Bulge ◽  
Colour Class ◽  
The Galaxy ◽  
Nearby Stars

As a preparation to the HIPPARCOS mission, a large observing programme on NLTT stars (propermotion > 0.18 ″/yr) was started in Genevaphotometry. The original programme consists of 10047 stars brighter than mR = 11.5, or mR = 12.5 if of colour class m. Among them, 7813 targets could be included in the HIPPARCOS programme, selected according to their observability and internal priorities in favour of large parallaxe stars (photometric distances < 100 pc) and high-velocity stars. The bulk of new nearby, halo, mild-metal poor and SMR stars in the HIP Catalogue originates from this proposal (N° 139). No less than 208 new nearby stars with π ≥ 40 mas were discovered south of δ +10°, the closest has π(HIP)= 182 mas. Radial velocities were obtained with CORAVEL at OHP and ESO. Most aspects of the early evolution of the Galaxy may be addressed with this sample. Here we discuss, as examples, the ages of the thick disk and of the galactic bulge.

scholarly journals SiO maser survey of evolved stars in the Galaxy: various environments of maser sources

2007 ◽  
Vol 3 (S242) ◽  
pp. 200-207 ◽  
Author(s):  
Shuji Deguchi
Keyword(s):  
Globular Clusters ◽  
Massive Star ◽  
Star Cluster ◽  
Agb Stars ◽  
Color Selection ◽  
Evolved Stars ◽  
Open Star ◽  
The Galaxy ◽  
Maser Sources ◽  
Open Star Cluster

AbstractUsing the SiO J=1−0 v=1 and v=2 lines near 43 GHz, we have detected about 2000 of 3600 sources observed with the Nobeyama 45-m radio telescope. The sources were chosen from IRAS/MSX/2MASS catalogs using color-selection criteria to pick up mass-losing oxygen-rich AGB stars and some post-AGB objects. A number of interesting sources were also found: supergiants in a massive star cluster, a nova with light echo (V838 Mon), AGB stars in globular clusters, and AGB candidates associated with dwarf galaxies. With the exception of the stars in the massive open star cluster, these ‘unusual’ objects are associated with metal poor environments where mass losing oxygen-rich AGB stars are unexpected. It is inferred that these objects were created by stellar merging which can occur in dense star clusters.

scholarly journals Stellar molecular jets traced by maser emission

2007 ◽  
Vol 3 (S242) ◽  
pp. 279-286 ◽  
Author(s):  
Hiroshi Imai
Keyword(s):  
Planetary Nebulae ◽  
Evolutionary Status ◽  
Agb Stars ◽  
Maser Emission ◽  
Vlbi Observations ◽  
Stellar Jets ◽  
The Galaxy ◽  
Host Stars ◽  
Maser Sources

AbstractHighly collimated jets found in AGB and post-AGB stars are expected to play an important role for shaping planetary nebulae. Recent VLBI observations of H2o maser sources have revealed that some of the spatio-kinematical structures of H2o maser sources exhibit stellar jets with extremely spatially and kinematically high collimation. Such stellar H2o maser jets, so-called “water fountains”, have been identified in about 10 sources to date. Here we review recent VLBI observations and relevant observational results of the water fountain sources. They have revealed a typical dynamical age and the detailed kinematical structures of the water fountains, the possibility of the existence of “equatorial flows”, and the evolutionary status of the host stars. The location and kinematics of one of the water fountain sources in the Galaxy is also revealed and shown here.

Interstellar gas in the central region of the Galaxy

1967 ◽  
Vol 31 ◽  
pp. 239-251 ◽  
Author(s):  
F. J. Kerr
Keyword(s):  
Central Region ◽  
Galactic Plane ◽  
Neutral Hydrogen ◽  
Continuum Emission ◽  
Galactic Centre ◽  
Interstellar Gas ◽  
Hydrogen Recombination ◽  
The Galaxy ◽  
Centre Region ◽  
The Relationship

A review is given of information on the galactic-centre region obtained from recent observations of the 21-cm line from neutral hydrogen, the 18-cm group of OH lines, a hydrogen recombination line at 6 cm wavelength, and the continuum emission from ionized hydrogen.Both inward and outward motions are important in this region, in addition to rotation. Several types of observation indicate the presence of material in features inclined to the galactic plane. The relationship between the H and OH concentrations is not yet clear, but a rough picture of the central region can be proposed.

Bipolar outflow of gas in the spiral galaxy NGC 3079

1986 ◽  
Vol 64 (4) ◽  
pp. 531-535 ◽  
Author(s):  
Nebojsa Duric ◽  
E. R. Seaquist
Keyword(s):  
Spectral Index ◽  
Spiral Galaxy ◽  
Central Region ◽  
Qualitative Description ◽  
Radio Continuum ◽  
Large Array ◽  
Very Large Array ◽  
Bipolar Outflow ◽  
The Galaxy

Very large array, radio-continuum observations of the edge-on spiral galaxy NGC 3079 are presented. The observations reveal that the nucleus has windlike properties and that the central region of the galaxy exhibits an unusual figure-eight morphology that shows evidence of severe depolarization and a flattening spectral index away from the nucleus. A qualitative description of a model is presented to account for the observed radio properties. It is shown that a wind-driven shock propagating away from the nucleus and focused by the ambient disk gas can give rise to the observed morphology.

scholarly journals A quantitative spectral analysis of 14 hypervelocity stars from the MMT survey

2018 ◽  
Vol 615 ◽  
pp. L5 ◽  
Author(s):  
A. Irrgang ◽  
S. Kreuzer ◽  
U. Heber ◽  
W. Brown
Keyword(s):  
Main Sequence ◽  
Galactic Center ◽  
Radial Velocities ◽  
Stellar Ages ◽  
The Galaxy ◽  
Quantitative Spectral Analysis ◽  
Kinematic Studies ◽  
Ejection Mechanism ◽  
Photometric Measurements ◽  
Stellar Masses

Context. Hypervelocity stars (HVSs) travel so fast that they may leave the Galaxy. The tidal disruption of a binary system by the supermassive black hole in the Galactic center is widely assumed to be their ejection mechanism. Aims. To test the hypothesis of an origin in the Galactic center using kinematic investigations, the current space velocities of the HVSs need to be determined. With the advent of Gaia’s second data release, accurate radial velocities from spectroscopy are complemented by proper motion measurements of unprecedented quality. Based on a new spectroscopic analysis method, we provide revised distances and stellar ages, both of which are crucial to unravel the nature of the HVSs. Methods. We reanalyzed low-resolution optical spectra of 14 HVSs from the MMT HVS survey using a new grid of synthetic spectra, which account for deviations from local thermodynamic equilibrium, to derive effective temperatures, surface gravities, radial velocities, and projected rotational velocities. Stellar masses, radii, and ages were then determined by comparison with stellar evolutionary models that account for rotation. Finally, these results were combined with photometric measurements to obtain spectroscopic distances. Results. The resulting atmospheric parameters are consistent with those of main sequence stars with masses in the range 2.5–5.0 M⊙. The majority of the stars rotate at fast speeds, providing further evidence for their main sequence nature. Stellar ages range from 90 to 400 Myr and distances (with typical 1σ-uncertainties of about 10–15%) from 30 to 100 kpc. Except for one object (B 711), which we reclassify as A-type star, all stars are of spectral type B. Conclusions. The spectroscopic distances and stellar ages derived here are key ingredients for upcoming kinematic studies of HVSs based on Gaia proper motions.

scholarly journals Survey of Surveys I. The largest catalogue of radial velocities for the Galaxy

2021 ◽  
Author(s):  
M. Tsantaki ◽  
E. Pancino ◽  
P. Marrese ◽  
S. Marinoni ◽  
M. Rainer ◽  
...  
Keyword(s):  
Radial Velocities ◽  
The Galaxy

scholarly journals Planetary nebulae in the inner Milky Way

2009 ◽  
Vol 5 (S265) ◽  
pp. 354-355
Author(s):  
Oscar Cavichia ◽  
Roberto D. D. Costa ◽  
Walter J. Maciel
Keyword(s):  
Statistical Analysis ◽  
Milky Way ◽  
Planetary Nebulae ◽  
Galactic Bulge ◽  
Intermediate Mass ◽  
Disk Interface ◽  
The Galaxy ◽  
Outer Border ◽  
Good Agreement

AbstractNew abundances of planetary nebulae located towards the bulge of the Galaxy are derived based on observations made at LNA (Brazil). We present accurate abundances of the elements He, N, S, O, Ar, and Ne for 56 PNe located towards the galactic bulge. The data shows a good agreement with other results in the literature, in the sense that the distribution of the abundances is similar to those works. From the statistical analysis performed, we can suggest a bulge-disk interface at 2.2 kpc for the intermediate mass population, marking therefore the outer border of the bulge and inner border of the disk.

scholarly journals Results of the SiO Maser Survey of the Galactic Bulge IRAS Sources

1996 ◽  
Vol 169 ◽  
pp. 119-124
Author(s):  
S. Deguchi ◽  
N. Ukita ◽  
H. Izumiura ◽  
T. Ono ◽  
Y. Nakada ◽  
...  
Keyword(s):  
Point Source ◽  
Near Infrared ◽  
Radial Velocities ◽  
Galactic Bulge ◽  
Entire Region ◽  
Dust Extinction ◽  
Optical Wavelengths

Evidence for the bar structure in our Galaxy has been shown by Blitz and Spergel (1991b) based on the near-infrared maps of the bulge, by Nakada et al. (1991) based on IRAS point source catalogue, and more clearly by recent COBE maps. However, no clear “dynamical” signature of the bulge bar has been found yet. At optical wavelengths, stellar radial velocities of the bulge stars were observed only at the optical windows and were not observed for the entire region of the bulge because of the dust extinction in this direction.

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