scholarly journals Evidence for coupling of evolved star atmospheres and spiral arms of the Milky Way

2020 ◽  
Vol 495 (1) ◽  
pp. 726-733 ◽  
Author(s):  
Mark D Gorski ◽  
Pauline Barmby
Keyword(s):  
Interstellar Medium ◽  
Milky Way ◽  
Spiral Structure ◽  
Spiral Arms ◽  
Evolved Stars ◽  
Data Release ◽  
Water Masers

ABSTRACT It is imperative to map the strength and distribution of feedback in galaxies to understand how feedback affects galactic ecosystems. H2O masers act as indicators of energy injection into the interstellar medium. Our goal is to measure the strength and distribution of feedback traced by water masers in the Milky Way. We identify optical counterparts to H2O masers discovered by the HOPS survey. The distribution and luminosities of H2O masers in the Milky Way are determined using parallax measurements derived from the second Gaia Data Release. We provide evidence of a correlation between evolved stars, as traced by H2O masers, and the spiral structure of the Milky Way, suggesting a link between evolved stars and the Galactic environment.

scholarly journals The spiral structure of our Milky Way

2012 ◽  
Vol 8 (S292) ◽  
pp. 106-106
Author(s):  
L. G. Hou ◽  
J. L. Han
Keyword(s):  
Milky Way ◽  
Spiral Structure ◽  
Hii Regions ◽  
Giant Molecular Clouds ◽  
Constant Weight ◽  
Spiral Arms ◽  
Flat Rotation Curve ◽  
Methanol Masers ◽  
The Masses ◽  
Excitation Parameters

AbstractThe spiral structure of our Milky Way has not yet been well outlined. HII regions, giant molecular clouds (GMCs) and 6.7-GHz methanol masers are primary tracers for spiral arms. We collect and update the database of these tracers which has been used in Hou et al. (2009) for the spiral arms.The new database consists of ∼ 2000 HII regions, ∼ 1300 GMCs and ∼ 800 methanol masers (6.7 GHz). If the photometric or trigonometric distance for any tracer is available from the literature, we will adopt it. Otherwise, we have to use the kinematic distance. We modify the VLSR according to the newly determined solar motions (U0 = 10.27 km s−1, V0 = 15.32 km s−1 and W0 = 7.74 km s−1, Schönrich et al. 2010), then calculate the kinematic distances with a flat rotation curve (R0 = 8.3 kpc, θ0 = 239 km s−1, Brunthaler et al. 2011). Very important step is that we weight tracers according to the excitation parameters of HII regions or the masses of GMCs, and a constant weight for masers. All three kinds of tracers are used together to outline the spiral structure (Fig. 1). A contour and gray map is constructed after we made a Gaussian extension for the tracers with the amplitude of weighting parameter.

scholarly journals The SEDIGISM survey: First Data Release and overview of the Galactic structure

2020 ◽  
Vol 500 (3) ◽  
pp. 3064-3082 ◽  
Author(s):  
F Schuller ◽  
J S Urquhart ◽  
T Csengeri ◽  
D Colombo ◽  
A Duarte-Cabral ◽  
...  
Keyword(s):  
Interstellar Medium ◽  
Large Scale ◽  
Galactic Plane ◽  
Structural Features ◽  
Galactic Centre ◽  
Molecular Gas ◽  
Spiral Arms ◽  
Star Forming ◽  
Wide Range ◽  
Data Release

ABSTRACT The SEDIGISM (Structure, Excitation and Dynamics of the Inner Galactic Interstellar Medium) survey used the APEX telescope to map 84 deg2 of the Galactic plane between ℓ = −60° and +31° in several molecular transitions, including 13CO (2 – 1) and C18O (2 – 1), thus probing the moderately dense (∼103 cm−3) component of the interstellar medium. With an angular resolution of 30 arcsec and a typical 1σ sensitivity of 0.8–1.0 K at 0.25 km s−1 velocity resolution, it gives access to a wide range of structures, from individual star-forming clumps to giant molecular clouds and complexes. The coverage includes a good fraction of the first and fourth Galactic quadrants, allowing us to constrain the large-scale distribution of cold molecular gas in the inner Galaxy. In this paper, we provide an updated overview of the full survey and the data reduction procedures used. We also assess the quality of these data and describe the data products that are being made publicly available as part of this First Data Release (DR1). We present integrated maps and position–velocity maps of the molecular gas and use these to investigate the correlation between the molecular gas and the large-scale structural features of the Milky Way such as the spiral arms, Galactic bar and Galactic Centre. We find that approximately 60 per cent of the molecular gas is associated with the spiral arms and these appear as strong intensity peaks in the derived Galactocentric distribution. We also find strong peaks in intensity at specific longitudes that correspond to the Galactic Centre and well-known star-forming complexes, revealing that the 13CO emission is concentrated in a small number of complexes rather than evenly distributed along spiral arms.

scholarly journals ATOMIUM: A high-resolution view on the highly asymmetric wind of the AGB star π1Gruis

2020 ◽  
Vol 644 ◽  
pp. A61
Author(s):  
Ward Homan ◽  
Miguel Montargès ◽  
Bannawit Pimpanuwat ◽  
Anita M. S. Richards ◽  
Sofia H. J. Wallström ◽  
...  
Keyword(s):  
Spiral Structure ◽  
Asymptotic Giant Branch ◽  
Spiral Arms ◽  
Evolved Stars ◽  
Crossing Time ◽  
Trend Breaks ◽  
Circumstellar Environments ◽  
Circumstellar Environment ◽  
Co Emission ◽  
The Continuum

The nebular circumstellar environments of cool evolved stars are known to harbour a rich morphological complexity of gaseous structures on different length scales. A large part of these density structures are thought to be brought about by the interaction of the stellar wind with a close companion. The S-type asymptotic giant branch (AGB) star π1Gruis, which has a known companion at ∼440 au and is thought to harbour a second, closer-by (< 10 au) companion, was observed with the Atacama Large Millimeter/submillimeter Array as part of the ATOMIUM Large programme. In this work, the brightest CO, SiO, and HCN molecular line transitions are analysed. The continuum map shows two maxima, separated by 0.04″ (6 au). The CO data unambiguously reveal that π1Gru’s circumstellar environment harbours an inclined, radially outflowing, equatorial density enhancement. It contains a spiral structure at an angle of ∼38 ± 3° with the line-of-sight. The HCN emission in the inner wind reveals a clockwise spiral, with a dynamical crossing time of the spiral arms consistent with a companion at a distance of 0.04″ from the AGB star, which is in agreement with the position of the secondary continuum peak. The inner wind dynamics imply a large acceleration region, consistent with a beta-law power of ∼6. The CO emission suggests that the spiral is approximately Archimedean within 5″, beyond which this trend breaks down as the succession of the spiral arms becomes less periodic. The SiO emission at scales smaller than 0.5″ exhibits signatures of gas in rotation, which is found to fit the expected behaviour of gas in the wind-companion interaction zone. An investigation of SiO maser emission reveals what could be a stream of gas accelerating from the surface of the AGB star to the companion. Using these dynamics, we have tentatively derived an upper limit on the companion mass to be ∼1.1 M⊙.

scholarly journals Synthetic observations of spiral arm tracers of a simulated Milky Way analog

2020 ◽  
Vol 642 ◽  
pp. A201 ◽  
Author(s):  
S. Reissl ◽  
J. M. Stil ◽  
E. Chen ◽  
R. G. Treß ◽  
M. C. Sormani ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Interstellar Medium ◽  
Faraday Rotation ◽  
Milky Way ◽  
Line Of Sight ◽  
Unit Distance ◽  
Spiral Arms ◽  
Rotation Measure ◽  
The Magnetic Field ◽  
Spiral Arm

Context. The Faraday rotation measure (RM) is often used to study the magnetic field strength and orientation within the ionized medium of the Milky Way. Recent observations indicate an RM magnitude in the spiral arms that exceeds the commonly assumed range. This raises the question of how and under what conditions spiral arms create such strong Faraday rotation. Aims. We investigate the effect of spiral arms on Galactic Faraday rotation through shock compression of the interstellar medium. It has recently been suggested that the Sagittarius spiral arm creates a strong peak in Faraday rotation where the line of sight is tangent to the arm, and that enhanced Faraday rotation follows along side lines which intersect the arm. Here our aim is to understand the physical conditions that may give rise to this effect and the role of viewing geometry. Methods. We apply a magnetohydrodynamic simulation of the multi-phase interstellar medium in a Milky Way-type spiral galaxy disk in combination with radiative transfer in order to evaluate different tracers of spiral arm structures. For observers embedded in the disk, dust intensity, synchrotron emission, and the kinematics of molecular gas observations are derived to identify which spiral arm tangents are observable. Faraday rotation measures are calculated through the disk and evaluated in the context of different observer positions. The observer’s perspectives are related to the parameters of the local bubbles surrounding the observer and their contribution to the total Faraday rotation measure along the line of sight. Results. We reproduce a scattering of tangent points for the different tracers of about 6° per spiral arm similar to the Milky Way. For the RM, the model shows that compression of the interstellar medium and associated amplification of the magnetic field in spiral arms enhances Faraday rotation by a few hundred rad m−2 in addition to the mean contribution of the disk. The arm–interarm contrast in Faraday rotation per unit distance along the line of sight is approximately ~10 in the inner Galaxy, fading to ~2 in the outer Galaxy in tandem with the waning contrast of other tracers of spiral arms. We identify a shark fin pattern in the RM Milky Way observations and in the synthetic data that is characteristic for a galaxy with spiral arms.

scholarly journals Astrometry of water masers in post-AGB stars

2012 ◽  
Vol 8 (S287) ◽  
pp. 411-412
Author(s):  
Hiroshi Imai ◽  
Keyword(s):  
Milky Way ◽  
Agb Stars ◽  
Milky Way Galaxy ◽  
Evolved Stars ◽  
Intermediate Mass Stars ◽  
Source Distance ◽  
True Source ◽  
Trigonometric Parallaxes ◽  
Water Masers ◽  
Maser Sources

AbstractMeasurements of trigonometric parallaxes and secular motions of evolved stars, especially post-AGB stars including central objects of planetary nebulae and water fountain sources as well as peculiar or unclassified stars, provide unambiguous source distance scales and information on their orbits in the Milky Way Galaxy. True source luminosities and kinematical properties should lead us to elucidate the true characteristics and evolutional tracks of these stars. Here we present the recent results of astrometry towards H2O maser sources with the VLBI Exploration of Radio Astormetry (VERA). The target sources include a planetary nebula (K3–35), a pre-PN (IRAS 19312+1950), a water fountain (IRAS 18286−0959) and a K-type star (IRAS 22480+6002). We have demonstrated that parental stars of the former three sources should be intermediate-mass stars from their luminosities and orbits in the Milky Way. It is suggested that IRAS 22480+6002 should be a K-type supergiant previously suggested rather than an RV Tau variable star.

Progress on 21 cm Studies of the Southern Milky Way _

1975 ◽  
Vol 2 (6) ◽  
pp. 364-365 ◽  
Author(s):  
F.J. Kerr
Keyword(s):  
Milky Way ◽  
Spiral Structure ◽  
Radial Velocities ◽  
Straightforward Manner ◽  
Spiral Arms ◽  
Distance Transformation ◽  
Galactic Spiral Structure ◽  
Structure Problem ◽  
Galactic Spiral

In the first decade or so of 21 cm studies the galactic spiral structure problem was treated in a very straightforward manner. A simple velocity-distance transformation was used to derive the locations of the spiral arms from the radial velocities of the main features on the 21 cm profiles. Some well-known diagrams were obtained in this way.

scholarly journals The discovery of the spiral arms of the Milky Way

1985 ◽  
Vol 106 ◽  
pp. 59-70 ◽  
Author(s):  
Owen Gingerich
Keyword(s):  
Milky Way ◽  
Spiral Structure ◽  
Stellar Populations ◽  
H Ii Regions ◽  
Full Paper ◽  
Spiral Arms ◽  
Counting Methods ◽  
Luminous Objects ◽  
Observational Program

Attempts in the 1930s and 1940s to determine the spiral structure of the Milky Way by star counting methods, essentially the continuation of the work of the Kapteyn Astronomical Laboratory, failed to reach this goal. A new foundation for the search was laid by Walter Baade in his studies of stellar populations. With the recognition that highly luminous objects, especially H II regions, would outline the spiral structure, W.W. Morgan and his young associates Sharpless and Osterbrock carried out the observational program that first delineated, in 1951, the nearby arms of the Milky Way. The full paper was never published, so the historical details have remained somewhat vague, primarily because the 21-cm discoveries so quickly overtook the optical researches.

scholarly journals Formation and evolution of spiral arms in galaxies orbiting a Virgo-like cluster

2016 ◽  
Vol 11 (S321) ◽  
pp. 129-129
Author(s):  
Marcin Semczuk ◽  
Ewa L. Łokas
Keyword(s):  
Cluster Size ◽  
Milky Way ◽  
Spiral Structure ◽  
Tidal Force ◽  
Dark Matter Halo ◽  
Spiral Arms ◽  
Tidal Interactions ◽  
Grand Design ◽  
Formation And Evolution ◽  
Open Question

AbstractThe origin of spiral structure in disks of galaxies remains an open question. One of the theories predicts that two-armed, grand design spiral arms originate from tidal interactions with another body. Using N-body simulations we find that a Milky Way-like galaxy can develop spiral arms due to tidal force from a cluster-size dark matter halo.

scholarly journals Hic sunt dracones: Cartography of the Milky Way spiral arms and bar resonances with Gaia Data Release 2

2020 ◽  
Vol 634 ◽  
pp. L8 ◽  
Author(s):  
S. Khoperskov ◽  
O. Gerhard ◽  
P. Di Matteo ◽  
M. Haywood ◽  
D. Katz ◽  
...  
Keyword(s):  
Phase Space ◽  
Milky Way ◽  
Solar Radius ◽  
Spiral Arms ◽  
Full Phase Space ◽  
Spatial Coverage ◽  
Data Release ◽  
Space Data ◽  
First Time ◽  
Stellar Density

In this paper we introduce a new method for analysing Milky Way phase-space which allows us to reveal the imprint left by the Milky Way bar and spiral arms on the stars with full phase-space data in Gaia Data Release 2. The unprecedented quality and extended spatial coverage of these data allowed us to discover six prominent stellar density structures in the disc to a distance of 5 kpc from the Sun. Four of these structures correspond to the spiral arms detected previously in the gas and young stars (Scutum-Centaurus, Sagittarius, Local, and Perseus). The remaining two are associated with the main resonances of the Milky Way bar where corotation is placed at around 6.2 kpc and the outer Lindblad resonance beyond the solar radius, at around 9 kpc. For the first time we provide evidence of the imprint left by spiral arms and resonances in the stellar densities not relying on a specific tracer, through enhancing the signatures left by these asymmetries. Our method offers new avenues for studying how the stellar populations in our Galaxy are shaped.

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